id,title,context,question,answers
7,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What symptoms did the people had?,"{'answer_start': [3200], 'text': ['acute gastroenteritis']}"
18,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What type of samples were analyzed?
","{'answer_start': [1835], 'text': ['stool samples']}"
16,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What caused the event?,"{'answer_start': [4357], 'text': ['heavy faecal contamination of the raw water from Gta lv river']}"
18,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What symptoms did people report?,"{'answer_start': [1760], 'text': ['acute gastroenteritis']}"
22,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What were the first steps of investigation?,"{'answer_start': [1590], 'text': ['questionnaires']}"
20,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What is the date of the event?
","{'answer_start': [71], 'text': ['2008']}"
34,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What is the location of the event?
","{'answer_start': [61], 'text': ['Sweden']}"
14,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What pathogen was connected to the outbreak?,"{'answer_start': [3738], 'text': ['faecal indicator bacteria and coliphages']}"
31,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What is the source that started the event?
","{'answer_start': [4224], 'text': ['contaminated drinking water']}"
30,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","How was the event first detected?
","{'answer_start': [152], 'text': ['unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms']}"
29,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","How many people were ill?
","{'answer_start': [3069], 'text': ['2000']}"
19,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What are the pathogens?
","{'answer_start': [3119], 'text': ['NoV']}"
11,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [3780], 'text': ['300 plaque- forming units (p.f.u.)/100 ml']}"
23,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What are the symptoms?
","{'answer_start': [222], 'text': ['gastrointestinal symptoms']}"
34,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What is the concentration of the pathogen?
","{'answer_start': [3924], 'text': ['between 4 and 42 p.f.u./100 ml']}"
19,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What is the event?
","{'answer_start': [0], 'text': ['A large waterborne outbreak of NoV']}"
26,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What are the initial steps of investigation?
","{'answer_start': [786], 'text': ['identify the causative agents, the extent of the outbreak and possible sources of infection']}"
13,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What are the first steps of mitigation?
","{'answer_start': [699], 'text': ['boil water recommendation']}"
16,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What type of samples were examined?
","{'answer_start': [2041], 'text': ['Water samples']}"
26,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What did the authorities do to mitigate the event?,"{'answer_start': [905], 'text': ['inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms.']}"
9,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
","What was the age of the affected people?
","{'answer_start': [1697], 'text': ['19 and 75 years']}"
15,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What is the source of contamination?,"{'answer_start': [644], 'text': ['drinking water']}"
32,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What was the alert of the event?,"{'answer_start': [1308], 'text': ['notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms']}"
28,Contamination Question Answering,"A large waterborne outbreak of NoV occurred in Lilla Edet in Sweden in 2008. On 11 September 2008, the County Medical Ofcer (CMO) was informed about an unusually high number of individuals who had suddenly fallen ill with gastrointestinal symptoms during the previous days in Lilla Edet, a small municipality in southwest Sweden. Cases of gastroenteritis were reported from different places in the municipality, e.g. from the nursery schools, schools, nursing homes and from the Primary Healthcare Centre (PHC). The CMO notified the Environmental Office in the municipality about the ongoing outbreak. As the initial information indicated that drinking water was a possible source of the outbreak a boil water recommendation was issued on the same day. Investigations were initiated to identify the causative agents, the extent of the outbreak and possible sources of infection. Efforts were also made to inform the inhabitants in the municipality about the ongoing outbreak, the issued boil water recommendation, and medical advice for people with gastrointestinal symptoms. Information was spread via the media, the homepage of the municipality website, posters and local radio as VMA, i.e important message to the public. In addition to the cases reported from the municipality of Lilla Edet, the CMO was notified that 7/17 athletes of a team that had visited the municipality during the afternoon on 7 September had fallen ill with gastrointestinal symptoms 2 days after their visit. To estimate the proportion of the 13000 inhabitants in Lilla Edet that fell sick during the outbreak, questionnaires were sent by mail on 19 September to 1199 randomly selected inhabitants between the ages of 19 and 75 years. A case was defined as a household member with acute gastroenteritis with date of onset between 5 and 21 September. Fifty stool samples from outpatients with symptoms of acute gastroenteritis attending Lilla Edet PHC during 12-26 September were collected and examined for enteric pathogens, as described by Nenonen et al. [20]. Water samples, i.e. raw water from the Gta lv river, drinking water from different parts of the distribution network, and water from reservoirs in Lilla Edet, were collected on 12 September and analyzed at the microbiological laboratory at SMI for the presence of E. coli and coliform bacteria by Colilert 18 (IDEXX, USA), intestinal enterococci by Enterolert (IDEXX), (oo)cysts of Giardia spp. and Cryptosporidium spp. according to ISO 15553:2006, Clostridium perfringens according to ISO/CD 6461-2:2002, somatic coliphages according to ISO 10705-1:2000, Campylobacter spp. by culture on CCDA agar (in-house method), Salmonella spp. according to ISO 6340:1995, Verotoxin-producing E. coli (VTEC) by PCR screening for vt genes and NoV by seminested PCR [22]. Additional water samples were collected on 17 September and analyzed for presence of NoV and coliphages. From the questionnaire survey it could be calculated that out of the 7500 inhabitant that lived in households supplied by drinking water from Lilla Edet WTP, about 2000 (26.7%) fell ill with acute gastroenteritis. NoV was detected in 33/50 stool samples collected from patients with symptoms of acute gastroenteritis. NoV strains of genogroup I (GI) predominated in 31 of these samples and mixed genotypes of GI infections occurred in ve samples, as described by Nenonen et al. [20]. Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples. In samples from the drinking water system in Lilla Edet collected on 12 September, E. coli, coliforms, enterococci, Giardia, Cryptosporidium, Clostridium, Campylobacter or NoV could not be detected, while faecal indicator bacteria and coliphages [300 plaque- forming units (p.f.u.)/100 ml] were found in raw water samples from the Gta lv river. However, somatic coliphages in concentrations between 4 and 42 p.f.u./100 ml were detected in samples from the drinking water system collected on 17 September and in samples from the raw water collected on the same date. In the Lilla Edet outbreak early detection of NoV strain diversity in stool samples strengthened the initial hypothesis that contaminated drinking water was the point source. Thus, the waterborne outbreak in Lilla Edet was most probably a consequence of the heavy faecal contamination of the raw water from Gta lv river [20]. 
",What were the associated pathogens of concern?,"{'answer_start': [3389], 'text': ['Adenovirus was detected in one, sapovirus in one and rotavirus in three stool samples. Campylobacter spp. were isolated from two stool samples.']}"
20,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What type of samples were analyzed?
","{'answer_start': [461], 'text': ['Stool specimens']}"
22,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
",What caused the event?,"{'answer_start': [1380], 'text': ['contamination of a coastal lagoon']}"
21,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
",What symptoms did people report?,"{'answer_start': [2333], 'text': ['vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps']}"
16,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the initial cause of the event?
","{'answer_start': [591], 'text': ['sewage contamination event impacting the lagoon']}"
28,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the date of the event?
","{'answer_start': [125], 'text': ['January 2017']}"
34,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the location of the event?
","{'answer_start': [111], 'text': ['South Africa']}"
27,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
",What pathogen was connected to the outbreak?,"{'answer_start': [2558], 'text': ['Aeromonas, enterovirus and EPEC']}"
5,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the source that started the event?
","{'answer_start': [2936], 'text': ['lagoon']}"
14,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","How was the event first detected?
","{'answer_start': [51], 'text': [' reported by healthcare workers']}"
10,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","How many people were ill?
","{'answer_start': [2183], 'text': ['311 cases']}"
9,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What are the pathogens?
","{'answer_start': [2485], 'text': ['NoV']}"
29,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [2709], 'text': ['The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively']}"
33,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What are the symptoms?
","{'answer_start': [917], 'text': ['diarrhoea and/or vomiting']}"
13,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the concentration of the pathogen?
","{'answer_start': [2848], 'text': ['The E. coli level was 1.93* 10^3 cfu/100 ml']}"
34,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the event?
","{'answer_start': [26], 'text': ['gastroenteritis cases was reported by healthcare workers']}"
33,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What are the initial steps of investigation?
","{'answer_start': [181], 'text': ['A case-control study was conducted']}"
19,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What is the duration of the event?
","{'answer_start': [1043], 'text': ['between 14 December 2016 and 5 January 2017']}"
24,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","From when until when the event happened
","{'answer_start': [1529], 'text': ['during December 2016 and January 2017']}"
26,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What type of samples were examined?
","{'answer_start': [1996], 'text': ['Water samples']}"
23,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
","What was the age of the affected people?
","{'answer_start': [2260], 'text': ['21 years']}"
14,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
",What is the source of contamination?,"{'answer_start': [632], 'text': ['lagoon']}"
5,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
",What was the alert of the event?,"{'answer_start': [736], 'text': ['the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms']}"
28,Contamination Question Answering,"An unexpected increase in gastroenteritis cases was reported by healthcare workers on the KwaZulu-Natal Coast, South Africa, January 2017 with >600 cases seen over a 3-week period. A case-control study was conducted to identify the source and risk factors associated with the outbreak so as to recommend control and prevention measures. Record review identified cases and controls and structured-telephonic interviews were conducted to obtain exposure history. Stool specimens were collected from 20 cases along with environmental samples and both screened for enteric pathogens. A reported sewage contamination event impacting the lagoon was the likely source with person-to-person spread perpetuating the outbreak. On 5 January 2017, the Outbreak Response Unit (ORU) of the National Institute for Communicable Diseases (NICD), SA, was alerted to a high number of persons falling ill with gastrointestinal symptoms (diarrhoea and/or vomiting) on the coast of KZN Province. The alert from health authorities in the KZN Province indicated that between 14 December 2016 and 5 January 2017, 690 people presented with gastrointestinal symptoms at a private hospital on the KZN south coast. Based on the available information at the time, which included local newspaper and online articles that reported a sewage spillage into a nearby lagoon; the investigating team hypothesised that contamination of a coastal lagoon could have led to the outbreak. The outbreak occurred within an urban community on the south coast of KZN Province during December 2016 and January 2017. A case-control study was conducted, with a case defined as a person of any age who presented to the private hospitals emergency department between 19 December 2016 and 6 January 2017 with an acute onset of diarrhoea and/or vomiting. Twenty acute phase stool specimens were collected from cases presenting to the hospital between 6 and 10 January 2017 and sent cooled to the Centre for Enteric Diseases (CED), NICD, for testing. Water samples were collected from the lagoon and a nearby wastewater treatment works discharge (final effluent), which drains into a river that flows into the lagoon (Fig. 1). A total of 311 cases and 126 controls were identified. The median age for the cases was 21 years (interquartile range 1040 years). The most common symptoms were vomiting (85%; 133/157), diarrhoea (73%; 115/157) and abdominal cramps (31%; 49/157). Of the 20 clinical specimens tested, 11 (55%) tested positive for NoV; nine were positive for NoV GI, while two were positive for NoV GII. Aeromonas, enterovirus and EPEC were also detected in one NoV GI-positive specimen and STEC in another NoV GI-positive specimen. Environmental samples The total coliform and thermotolerant (faecal) coliform counts in the lagoon water were 2.39* 10^4 and 9.5* 10^3 cfu/100 ml, respectively. The E. coli level was 1.93* 10^3 cfu/100 ml. These data support the hypothesis that the lagoon was the source of the outbreak among holiday-makers on the KZN Coast. The lagoon was reportedly contaminated by the wastewater treatment works effluent, which drained into the river flowing into the lagoon. 
",What were the associated pathogens of concern?,"{'answer_start': [2616], 'text': ['NoV GI']}"
20,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","What is the initial cause of the event?
","{'answer_start': [3461], 'text': ['run-off of rainwater contaminated  with faeces of breeding gulls']}"
19,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","What is the date of the event?
","{'answer_start': [3], 'text': ['May 2007']}"
9,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","What is the location of the event?
","{'answer_start': [82], 'text': ['North Holland']}"
19,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","How was the event first detected?
","{'answer_start': [2412], 'text': ['samples']}"
30,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","What are the pathogens?
","{'answer_start': [2387], 'text': ['E. coli']}"
32,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","What are the first steps of mitigation?
","{'answer_start': [146], 'text': ['boil tap water']}"
23,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

","What did they do to mitigate the event?
","{'answer_start': [2912], 'text': ['public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public']}"
9,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

",What did the authorities do to mitigate the event?,"{'answer_start': [2786], 'text': ['broadcasted through  mass-media including the national and regional television channel,  radio and newspapers.']}"
32,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

",What is the source of contamination?,"{'answer_start': [46], 'text': ['tap water']}"
27,Contamination Question Answering,"In May 2007, Escherichia coli was detected in tap water supplied  by a company in North Holland. The company issued advice through  mass media to boil tap water before consumption; this advice was  lifted six days later. A cross-sectional study was implemented to  investigate compliance among residents in this area. Based on  postcode, a total of 300 households, chosen randomly from a  database of a private company performing internet-based surveys  for different marketing purposes, were sent a self-administered  questionnaire for this study. The questionnaire contained questions  on demographic information, source of information regarding the  advice, response to it and personal opinions on the companys  reaction and the advice. Ninety-nine (66%) households of the  affected area and 90 (60%) households from non-affected areas  served by the same company replied to the survey. All respondents  knew about the advice. 81.8% of the respondents in the affected  area and 5.6% of the non-affected areas reported complying with  the advisory. Most respondents from the affected area still used  unboiled water to brush teeth, wash salads and fruits. There was no  difference in compliance between men and women. Using the mass  media was proved to be efficient to inform the public and could  be used in the future in similar settings. However, more detailed  wording of boiling advices should be considered in the future. Introduction Consumption of drinking water may cause waterborne disease  which can be prevented by protection of the source water, efficient  treatment processes and reliable distribution systems. The  European Union Drinking Water Directive [1] demands monitoring  of tap water for different parameters, such as Escherichia coli, to  indicate possible faecal contamination from humans and animals.  System failure or human error may cause an increase in the  level of pathogens in the water posing a risk of waterborne disease.  For example, in 2001, a large outbreak of gastroenteritis occurred  due to accidental introduction of partially treated water to the  drinking water supply system in the Netherlands, resulting in 921  households being exposed to contaminated water [2]. In the event that faecal contamination is detected the drinking  water company may issue an advice to boil tap water before using  it for domestic purposes. On 15 May 2007, E. coli was detected in  samples collected the day before of the finished tap water delivered  by a company in the province Noord-Holland (North-Holland) in the  Netherlands. For preventive reasons, on the same day the company  issued an advice for consumers to boil tap water for two minutes  before consumption but that this was not necessary for taking a  shower or washing. This information was broadcasted through  mass-media including the national and regional television channel,  radio and newspapers. In addition, a public website used during  emergency situations (www.crisis.nl) and a toll-free telephone  number were made available for the public to provide information  to households in the affected area. The boil water advice had an impact on approximately 180,000  households in the affected area comprising 13 municipalities.  The advice was lifted a week later, on 22 May 2007, as risk for  public health was no longer present. In September 2007, the water  company published a press release informing that the cause of the  water contamination was due to run-off of rainwater contaminated  with faeces of breeding gulls on the roof that had seeped into one  of the six storage rooms [3]. Elevated levels of microorganisms in drinking water may  represent a public health risk. For this reason, we investigated  compliance with boil water advice issued by the private water  company following the 2007 incident. Methods A cross-sectional study was implemented to investigate factors  that may have affected water consumption habits of the residents  in the area supplied by the water company. For this purpose, on  the companys behalf, a self-administered questionnaire was sent  to 300 households in June 2007. Households were selected on the  basis of their residence postcodes; half in the area where the advice  was valid and half in areas served by the same company but where  the advice did not apply. These participants were derived from a  database of a private company that conducts online consumer  surveys for marketing purposes.  The questionnaire contained questions on demographic  information, level of urbanisation, source and time of receiving the  information regarding the advice, initial and secondary response to  the advice and personal opinions on the companys response and  the advice itself. The data were sent back to the drinking water  company and the National Institute for Public Health and the  Environment, where they were analysed. The statistical analysis  was done with STATA v10. 2   EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org Results Ninety-nine households (66%) from the area affected by water  contamination and 90 households (60%) from control areas  supplied with water by the same company replied to the survey.  Women more often than men responded to the questionnaire  in both the affected and the non-affected areas (57.7% of all  responders). The respondents represented 189 households with a  total population of 505 people, 176 (34.9%) of whom were below  the age of 18 years. There was no statistically significant difference  in the number of children per household between the affected and  the non-affected areas (p=0.112). Descriptive results for the two  different areas are presented in Table 1. All 189 respondents (100%) in both areas answered that  they had been informed about the advice. Ninety-five (50.3%)  of them said they had first heard about it through the television.  Other sources were radio (24.3%), friends, relatives or neighbours  (22.8%), newspapers (19.6%) and the internet (7.4%). Persons living in the affected area were more frequently  disappointed (14.1%) about the choice of the company to use  mass media for the advice than people residing in the non- affected area (2.2%). In the affected area, seven (9.3%) of the  respondents had first reacted with fear to the information on the  possible contamination of water, 34 (45.3%) responded with self- control and 34 (45.3%) with the intention to take measures. The  corresponding percentages for the non affected area were 15.7%,  72.9% and 11.4%. About half (48.5%) of the respondents from the  affected area said they had looked for more information when they  had heard about the advice, while the corresponding proportion of  respondents from the non-affected area was only 8.9% (p<0.001).  The most common source of active search for more information was  the website of the water supply company. Eighty-one (81.8%) of all respondents in the affected area said  they had complied with the advice. This was done by buying bottled  water (43.4% of all respondents in affected area) or boiling tap  water for two minutes before consuming it (70.7%). None of the  respondents in the area stopped consuming tap water completely.  Five (5.6%) of the respondents in the non-affected area were  buying bottled water and three of them (3.3%) were boiling tap  water during the advice. These numbers were considerably lower  than the corresponding ones in the affected area, but showed that  compliance exceeded beyond the affected area. Even though it had not been advised to boil water for activities  such as washing and showering, 26 (26.3%) of the respondents  in the affected area stated that they had not been aware of that. Concerning the image of the drinking water company, 177  respondents (93.7%) thought that the company had done well  informing the consumers about the water contamination and its  response to it. This prevailing opinion was not different between  respondents from the affected area and those from the non affected  area. The respondents compliance with the advice was independent  of sex, age and the presence of children in the household. However,  the respondents were 138.6 times more likely to follow the advice  if a second person in the household was following it as well  (p<0.001). Reasons for non-compliance with the advice are given in Table 2. Some of the respondents replied that they had been using boiled  water for uses other than drinking, too. These results are shown  in Table 3. The majority of the respondents stated that their image of the  company had not changed after the incident and the six-day advice  (78.8% in the affected area and 88.9% in the non-affected area). Factors affecting compliance The type of mass media from which people in the affected  area found out about the advice played no significant role in the  subsequent compliance of the respondents. The highest compliance  rates occurred among those in the affected area who heard about  the advice from the internet (90%) or from friends (89.5%).  Respondents informed by more than one source were more likely  T a b l e  1 Survey on boil water advice in the North Holland province  in the Netherlands, 2007, demographic characteristics of the  respondents Affected area (n=99) Non-affected area (n=90) Total (n=189) p-value Respondents age  (years) 47.7 48.4 48.0 0.7549 Number of people  living in the household 2.62 2.82 2.72 0.2526 Number of children  living in the household 0.78 1.11 0.93 0.0510 T a b l e  2 Reasons for non-compliance with boil water advice in  the affected area in the North Holland province, the  Netherlands, 2007 (n=11) Reason given N % I have enough immunity 1 9.1 The risk was small 1 9.1 I was not worried 3 27.3 It was too much inconvenience 2 18.2 I forgot about it 2 18.2 I had only just found out 2 18.2 Total 11 100.0 T a b l e  3 Use of boiled water for uses other than drinking in the affected area  in the North Holland province, the Netherlands, 2007 (n=99) Domestic use N % To brush teeth 30 28.1 To wash salads 48 35.6 To wash fruits 51 48.4 To make coffee 56 54.7 To make ice cubes 89 87.2 To give to pets 73 69.4     EUROSURVEILLANCE  Vol. 14  Issue 12  26 March 2009  www.eurosurveillance.org  3 to have complied with the advice (90.9% against 79.2%) but  this difference was not statistically significant. The source of  information did not depend on the age (p=0.6532). Compliance  with the advice did not differ between households with children  and those without children (p=0.536). Respondents who undertook active search for more information  may have been more likely to follow the advice than those who did  not proceed to further active search for more information (89.4%  vs. 74.5%, p=0.058). Since all respondents knew about the advice, it was not possible  to estimate unwitting compliance rates. 

",What were the associated pathogens of concern?,"{'answer_start': [13], 'text': ['Escherichia coli']}"
5,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What symptoms did the people had?,"{'answer_start': [4068], 'text': ['diarrhea']}"
21,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What symptoms were developed?,"{'answer_start': [6940], 'text': ['diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool']}"
21,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What caused the event?,"{'answer_start': [18031], 'text': ['animal feces']}"
32,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",With what symptoms they were presented?,"{'answer_start': [4217], 'text': ['diarrhea']}"
8,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What symptoms did people report?,"{'answer_start': [3962], 'text': ['diarrhea']}"
31,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What were the first steps of investigation?,"{'answer_start': [5622], 'text': ['rainfall statistics']}"
28,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What is the date of the event?
","{'answer_start': [108], 'text': ['March 2000']}"
31,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What is the location of the event?
","{'answer_start': [82], 'text': ['northwest England']}"
20,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What pathogen was connected to the outbreak?,"{'answer_start': [216], 'text': ['Cryptosporidium oocysts']}"
33,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","How was the event first detected?
","{'answer_start': [3012], 'text': ['Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority.']}"
16,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","How many people were ill?
","{'answer_start': [120], 'text': ['Fifty-eight cases']}"
27,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What is the attack rate?
","{'answer_start': [7207], 'text': ['29.6 per 10,000 population']}"
32,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What are the pathogens?
","{'answer_start': [155], 'text': ['Cryptosporidium']}"
12,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [10252], 'text': ['76 oocysts of Cryptosporidium per 1,000 L']}"
12,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What are the symptoms?
","{'answer_start': [141], 'text': ['diarrhea']}"
22,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What is the concentration of the pathogen?
","{'answer_start': [10436], 'text': ['five oocysts per 10 L of water']}"
26,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What is the event?
","{'answer_start': [0], 'text': ['An outbreak of cryptosporidiosis']}"
10,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What are the initial steps of investigation?
","{'answer_start': [3587], 'text': ['interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire ']}"
5,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
","What was the age of the affected people?
","{'answer_start': [6787], 'text': ['from 7 months to 95 years, but most patients were ‹5 years']}"
30,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What is the source of contamination?,"{'answer_start': [17753], 'text': ['water supply']}"
13,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",How many cases were there?,"{'answer_start': [6469], 'text': ['Fifty-eight cases']}"
5,Contamination Question Answering,"An outbreak of cryptosporidiosis occurred in and around Clitheroe, Lancashire, in northwest England, during March 2000. Fifty-eight cases of diarrhea with Cryptosporidium identified in stool specimens were reported. Cryptosporidium oocysts were identified in samples from the water treatment works as well as domestic taps. Descriptive epidemiology suggested that drinking unboiled tap water in a single water zone was the common factor linking  cases. Environmental investigation suggested that contamination with animal feces was the likely source of the outbreak. This outbreak was unusual in that hydrodynamic modeling was used to give a good estimate of the peak oocyst count at the time of the contamination incident. The oocysts persistence in the water distribution system after switching to another water source was also unusual. This persistence may have been due to oocysts being entrapped within biofilm. Despite the con- tinued presence of oocysts, epidemiologic evidence suggested that no one became ill after the water source was changed.  Outbreaks of cryptosporidiosis associated with drinking water have been an emerging problem for the past 20 years. In the 1990s, cryptosporidiosis became the most common cause of outbreaks associated with public drinking water supplies in the United Kingdom (1). This disease is also responsible for several of the largest outbreaks of waterborne disease seen in the United States (1). Yet substantial areas of uncertainty over many aspects of the epidemiology of this infection remain. One of the most pressing such areas is deter- mining what concentration of oocysts in drinking water is con- sidered safe.  In the United Kingdom, recent legislation was enacted that set a legal limit of 1 oocyst/10 L when water was sampled con- tinuously over a 24-hour period (2). However, this level was set as a treatment standard and was not derived from known public health standards. With current knowledge, proposing standards for cryptosporidia based on public health criteria is not possible, primarily because published reports of outbreaks have not had accurate measures of the concentration of oocysts in the water at the time when infection was thought to have occurred. We report, to our knowledge, the first outbreak to have occurred when a fairly accurate estimate of the concen- tration of oocysts in the water could be made.  The Outbreak In March 2000, an outbreak of cryptosporidiosis occurred in and around the town of Clitheroe in Lancashire County in northwest England. This small market town, nestled in the hills near the Ribble River, is a thriving community that attracts many tourists. The surrounding countryside supports arable and dairy farming. Before this outbreak, reported cases of cryptosporidiosis were low. In the years 19971999, the mean annual attack rate of laboratory-confirmed cryptosporid- iosis was 4.83 per 10,000 residents per year, compared with 13.57 for the region as a whole. During March 115, 2000, the Ribble Valley Environmental Health Department reported nine cases of cryptosporidiosis to the East Lancashire Health Authority. All the patients lived in or near Clitheroe. Provisional information provided by the water company indicated that six of these nine patients lived in a single water zone supplied by the same water treatment works. On the basis of this information, an outbreak was declared, and an outbreak control team was established. The team met for the first time on March 16. Methods Epidemiologic Investigation Environmental health and public health department personnel interviewed patients with cryptosporidiosis in person or by telephone, using a structured questionnaire (3). Analysis was performed by using the computer program Epi-Info (version 6.02; Centers for Disease Control and Prevention, Atlanta, GA). Patients were defined as those with a positive stool sample who lived in or visited the implicated water zone and who had onset of diarrhea since March 1, 2000. Cases were defined as primary when no other member of the household had had diarrhea in the 2 weeks before the onset of symptoms; possible secondary cases were defined as those in which a member of the same household had had diarrhea in the previous 2 weeks. The case definitions included those who had traveled abroad for <7 days.  *East Lancashire Health Authority, Nelson, United Kingdom; United Utilities Water PLC, Warrington, United Kingdom; Public Health Labo- ratory, Preston, United Kingdom; and University of East Anglia, Nor- wich, United Kingdom O RESEARCH 620 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Microbiologic Investigation General practitioners in the area submitted stool samples to the local hospital microbiology laboratory. Stools were examined by microscopy with the modified auramine phenol stain (4). Positive samples were then sent to the Public Health Laboratory Services Cryptosporidium Reference Unit for genotyping.  Environmental Investigations The local water company provided information on the water supply, instituted a water-sampling schedule (from domestic properties, water treatment works, and fire hydrants during flushing operations), and analyzed the water samples to identify Cryptosporidium oocysts. Most of the samples were 10-L grab samples analyzed according to the U.K. standard method (5). The large-volume samples were analyzed by the method in the Water Supply (Water Quality) Amendment Reg- ulations of 1999 (2). The source of water to the affected area (Grindleton Springs) was visited by members of the outbreak control team. The local water company supplied rainfall statistics for the weeks preceding the outbreak. Local authority engineers were consulted for information on previous high water or flood warnings.  After the incident, the water company constructed a physical model of the affected reservoir, Lowcocks, with a geometric scaling ratio of 32:1. Flows were tracked by using salt injection with an array of conductivity probes suspended above the tank and injecting colored dyes for visualization. As the ratio of the two respective inlet flows can vary, the baseline performance of the tank was evaluated over a range of opera- tional, but steady state, conditions. A series of transient tests was then conducted to mirror the operation of the reservoir in the time leading up to and covering the incident until the boil water notice was issued on March 21.  Result Descriptive Epidemiology Fifty-eight cases met the case definition. Of these, three were in patients who had traveled abroad for <7 days in the 2 weeks before illness. Fifty-one cases were identified as pri- mary, and seven as possible secondary. The dates of onset of cases (Figure 1) showed peaks on March 10 and 17. Ages of patients ranged from 7 months to 95 years, but most patients were <5 years (52%). Thirty (52%) of the patients were male and 28 (48%) female. All 58 patients (100%) had diarrhea; 18 (31%) had fever, 48 (83%) abdominal pain, 19 (33%) vomit- ing, and three (5%) blood in the stool.  Fifty-one patients lived in the same water supply zone and drank unboiled main tap water in the zone. The crude attack rate for residents of this zone was 29.6 per 10,000 population (based on general practitioner registered population of 17,252 linked by postal code of residences in the water supply zone). The crude attack rate for people within the same local government area but not living in the same water supply zone was 1.8 per 10,000 population, giving a relative risk associated with residence in the implicated water supply zone of 16.2 (95% confidence interval 7.5 to 35.0). The age-specific attack rate varied from 275 per 10,000 in children <5 years of age to 5.6 per 10,000 in those >44 years (Table 1). Seven patients lived in properties not in the affected water zone. However, six of these had drunk unboiled main water in the affected zone in the 2 weeks before illness; the other patient had visited a swimming pool in the zone. Other potential risk factors, such as travel, visit to a swimming pool, and consumption of certain foods, were included in the questionnaire. None was common in patients. Microbiologic Testing Of the 58 cases with a positive stool sample for Cryptosporidium, 47 specimens were typed. All were C. parvum genotype 2 (for nine cases there was insufficient material, and two specimens were untypable). Environmental Results Water Sample Analysis Lowcocks Water Treatment Works (WTW), sourced from Grindleton Springs, supplied approximately 90% of the water to the affected zone. The supply was a spring source that fed a single service reservoir and from there moved into distribu- tion. However, the reservoir could also be filled from a nearby larger water supply via an aqueduct. The supply was chlori- nated but not filtered. As part of the risk assessment carried out under water quality amendment regulations (2), Lowcocks Figure 1. Date of diarrhea onset, 58 cryptosporidiosis cases,  Clitheroe, 2000.  Table 1. Age-specific attack rates for cryptosporidiosis in residents of  water zone 97, Clitheroe, March 2000 Age group Cases  (n=51) Population Rate/10,000 95% confidence interval <4 26 945 275.1 170.8 to 379.4 514 9 2,283 39.4 13.7 to 65.1 1544 12 6,822 17.6 7.6 to 27.5 >45 4 7,202 5.6 0.1 to 11.0 Total 51 1,7252 29.6 21.5 to 37.7 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 621 RESEARCH WTW was classified as being at significant risk from Cryptosporidium oocysts in water supplied from the works. However, continuous monitoring had not yet begun before the outbreak.  The reservoir is rectangular with two inlets and a single outlet. The tank is 110 m long and 90 m wide with an opera- tional depth between 3.5 m and 5.4 m. The spring has one inlet, which varies from 2 to 6 megaliters per day and another from the aqueduct, which varies from 1.5 to 5 megaliters per day. The calculated capacity of the reservoir is 53 megaliters. The ratio of aqueduct to spring water varies considerably dur- ing normal operation; full advantage is taken of the increase in availability of the springs source after major rainfalls.  On March 17, a large-volume sample of water (1,627 L) from a pumping station fed from Lowcocks WTW yielded 76 oocysts of Cryptosporidium per 1,000 L. Cryptosporidium oocysts were also identified in a water sample taken from a domestic tap in the water zone on March 16 at a concentration of five oocysts per 10 L of water. From March 16 to April 6, a total of 192 samples (10-L grab samples) from domestic taps or fire hydrants in the affected zone were analyzed; 47 (24%) contained Cryptosporidium oocysts in concentrations ranging from 1 to 9/10 L. Six water samples from domestic taps in areas adjoining the affected water zone were negative (Table 2, Figure 2). Site Visits The concrete casings of two of the Grindleton Springs col- lection chambers showed signs of aging and were in a poor state of repair (one could look directly into one chamber through holes in the concrete). Evidence of recent livestock excreta (cattle) was present in the areas around, and in direct contact with, the covers to several of the spring collection chambers; manure was also spread in a field within 5 m of one wellhead. Rainfall Statistics Abnormally heavy rainfall (up to 58 mm per day) and flood alerts were reported for the area on February 27 and March 27. Hydraulic Modeling A number of detailed transient state tests were conducted in which the flows and levels were altered in line with the res- ervoir operation before and during the outbreak. Initially, the first injection of oocysts was assumed to have come into the reservoir on February 27, after the first associated heavy rain- fall. However, results from these initial tests indicated that, because of the way the reservoir operated and its short nominal retention time (2 days) during part of this period, a large spike of oocysts entering the reservoir from the springs inlet on Feb- ruary 27 would have been effectively washed out by the time the sample was taken on March 17. Two potential contamination events, one after each major rainfall event on February 27 and March 2, respectively, were then proposed. This hypothesis was modeled by injection of two discrete salt pulses into the model springs inlet at the appropriately scaled time in the modeling run. Results indi- cated three peaks of oocyst counts at the tank outlet. The first peak occurred when the tank was operating on only spring flow, corresponding to February 29. The second peak came on March 1, when aqueduct flow was introduced. The final peak occurred on March 23, after the second salt pulse (simulating the rainfall incident).  Based on the concentration found in the March 17 sample, the most probable peak concentration that the Clitheroe popu- lation would have been exposed to was 40 times greater, approximately 30 oocysts per 10 L. These values are based on tests in which the pulse was introduced instantaneously; in practice, contamination likely took place over several hours or days after each major rainfall event. While it is likely that the behavior of oocysts would not substantially differ in the water system and the salt and dye model, these numbers should not be considered exact; rather, they are a good indication of level of exposure over the period in question. Table 2. Results of 10-L grab samples taken within distribution range  of water works during investigationa of cryptosporidial outbreak,  Clitheroe, March 16April 6, 2001 Date Samples  taken Samples  positive Oocyst counts of positive samples/L 16 Mar 3 1 0.5 17 Mar 6 5 0.1 0.2 0.1 0.2 0.1 18 Mar 8 4 0.2 0.2 0.3 0.3 19 Mar 8 5 0.2 0.3 0.1 0.1 0.2 20 Mar 9 5 0.1 0.2 0.9 0.5 0.1 21 Mar 23 5 0.2 0.1 0.1 0.4 0.1 22 Mar 16 4 0.1 0.1 0.1 0.1 23 Mar 15 2 0.1 0.2 24 Mar 15 2 0.1 0.1 25 Mar 12 2 0.1 0.1 26 Mar 12 0 27 Mar 9 0 28 Mar 3 2 0.3 0.4 29 Mar 3 0 30 Mar 6 3 0.1 0.2 0.4 31 Mar 9 3 0.1 0.1 0.6 1 Apr 7 1 0.1 2 Apr 7 1 0.1 3 Apr 6 2 0.1 0.1 4 Apr 6 0 5 Apr 6 0 6 Apr 3 0 a Total volume examined each day (in L) = 10 X number of samples taken. RESEARCH 622 Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 Control Measures At the first outbreak control team meeting, 11 of 14 reported cryptosporidiosis cases were known to be in residents of the same water supply zone. As a result, the water supply to the affected area was changed to an alternate supply during the following night, and the system was flushed. The alternate supply was an approximately 50/50 blend of filtered surface water from two separate (protected) upland impounding reser- voirs. The first source (Watchgate) provides up to 600 megali- ters per day to a population of approximately 1.75 x 106; the second source (Hodder) provides up to 50 megaliters per day to a population of approximately 1.75 x 103. Both areas had had no observed increase in the rates of reported cryptosporid- iosis. At the third outbreak control team meeting, when results of sampling became available, it became evident that, although the water supply to the area had been changed by 9:30 a.m. on March 17 (and its distribution throughout the zone confirmed by chemical analysis of domestic water samples), substantial numbers of Cryptosporidium oocysts still existed in samples taken during the next 4 days (March 1720). Initial samples from the source of the new water supply showed no evidence of contamination. Historic archived data available for both new sources showed only a low frequency of detected oocysts in the raw (untreated source) water for each site. During the incident, five samples of treated water were taken from the first site and 13 samples from the second source. A single oocyst was reported in one 10-L sample taken from the first site; no oocysts were detected in the other samples.  The outbreak control team agreed that there continued to be a risk to public health and issued a Boil Water Advisory on March 21. This advisory was rescinded on March 27 after extensive water system flushing operations and 2 days of domestic water samples being clear of Cryptosporidium oocysts. The peak in counts on March 28, although calculated from three samples, was associated with the sampling water from hydrants rather than from domestic taps.  Water sampling continued, but samples were taken from fire hydrants rather than domestic taps. While inspections of the water system showed no evidence of ongoing contamina- tion, analysis of water continued to show cryptosporidia. When oocysts were detected in hydrant samples after the source of water had been changed, experienced operations staff inspected the route of the aqueduct, and boundary valves at the periphery of the affected distribution system were checked to ensure that water could not enter this system from an adjacent zone.  At this stage, no further new cases of cryptosporidiosis were being reported. The original source of water, Grindleton Springs, had been identified as having a plausible source of oocysts within the watershed (cattle excreta), a plausible path- way (through the damaged spring head structure to one of the chambers), and inadequate treatment for removing oocysts (microfiltration with a pore size >40 ); this source of water had been isolated and discharged to waste. Thus, the change in sampling method, rather than ongoing contamination, might be causing the continuing positive oocyst results. For this rea- son, the boil water advisory was not reinstituted. Further flush- ing continued, no new cases of cryptosporidiosis were reported, and the last water sample positive for oocysts was on April 3.  Discussion Use of U.K. Public Health Laboratory Service guidelines strongly associated this outbreak with the water supply because Cryptosporidium oocysts were detected in treated water and the descriptive epidemiology suggested that drinking tap water was the only common factor linking the cases (6). Environmental investigations suggested that contamination of Grindleton Springs with animal feces was the probable cause of the outbreak. Results of genotyping were consistent with an animal source. This outbreak is unusual because of the very high attack rate of laboratory-confirmed cases. The crude attack rate for microbiologically confirmed cases of cryptosporidiosis was much higher than previously reported in the United Kingdom (79). We suggest that this high attack rate occurred because of low immunity in the population and the probable high con- centration of oocysts at the time of the initial contamination. Although we have no direct measure of population immunity before this outbreak, the incidence of infection in previous years was low compared with that in the rest of the region. Furthermore, until the outbreak, the water supply was a groundwater source; various groups have suggested that such sources are associated with lower sporadic infections and lower population immunity (7,10).  The other major issue raised by this outbreak was the impact of changing the source of water. The outbreak control team had suggested that changing the water supply to the affected area at the beginning of the outbreak would remove the Cryptosporidium oocysts from the water. However, this measure did not result in the expected immediate clearance of contamination. Indeed, despite lack of evidence of a new con- tamination source and with ongoing extensive flushing opera- tions, oocysts remained detectable at low levels for up to 19 days after the change. Counts did generally decline during the 10 days after the supply was changed; however, counts peaked on March 20 after a burst in the main supply pipe. Increased Figure 2. Mean daily cryptosporidia oocyst counts from 10-L grab  samples taken during outbreak investigation, Clitheroe. Emerging Infectious Diseases    Vol. 8, No. 6, June 2002 623 RESEARCH counts on March 2831 occurred when water samples started being taken from hydrants, rather than domestic taps. Hydrant water is discharged much more forcefully than that from domestic taps. The slow decline in oocyst counts after the change in supply may have been because of captured oocysts being released from the biofilm on the surface of the distribu- tion pipes. Subsequent peaks associated with the burst and use of hydrants for sampling could have increased oocyst counts by stripping biofilm from the inner surface. Cryptosporidium oocysts do attach to biofilm in this manner (1,11,12) Whatever the reasons for the continued detection of oocysts in water samples, few, if any, cases of infection were acquired after the source was changed. The epidemiologic analysis suggests that changing the water supply was the key public health measure. The boil-water advisory had little, if any, effect on reducing subsequent cases. The decision not to reintroduce the advisory when hydrant samples continued to show oocysts appears to have been justified. Monitoring water samples, particularly with 10-L small- volume samples, highlighted the difficulties in interpreting the public health importance of oocysts in the water (1315). Cur- rently, the level of detectable Cryptosporidium oocysts in domestic water samples that poses no public health risk is unknown. The number of oocysts detected in the large-volume filtration of water from the WTW was below the limit cur- rently defined as a national maximum permissible treatment standard (100 oocysts per 1,000 L) (2). However, this outbreak occurred 10 days after the most recent of three major rainfalls that could plausibly have given rise to contamination of the source water. Physical and computational fluid dynamics mod- eling suggested that the concentrations of oocysts in water leaving the WTW immediately after the heavy rainfall were 30 times the statutory treatment standard.  The introduction of continuous monitoring in the United Kingdom, together with existing surveillance for cryptosporid- ium infection in humans, will hopefully result in a better defi- nition of an appropriate public health standard for this organism. However, recent human studies have shown a sub- stantial intraspecies variability in the infectivity of Cryptospo- ridium oocysts (16). Furthermore, we have recently identified a novel strain of C. parvum that appears to be widespread in sheep but has never been described in humans (17). These observations suggest that identifying a standard in drinking water that would lead to a tolerable level of illness in the com- munity may not be possible. Indeed, outbreaks of cryptospo- ridiosis associated with drinking water elsewhere in the United Kingdom have occurred despite the peak oocyst counts being well within the statutory standard (18,19). Several episodes have also been reported in which high oocyst counts (>10 oocysts in 100 L) have been detected in treated water with no episodes of illness subsequently being detected in the commu- nity (20). Further research is required to define the public health importance of low levels of Cryptosporidium oocysts as well as the optimal water sampling strategy during an outbreak. Similarly, the effectiveness and utility of system flushing remain to be shown. The current treatment standard should be reviewed, as further evidence relating to the public health impact of levels of Cryptosporidium oocysts becomes avail- able.  Dr. Howe is a specialist registrar in public health medicine in northwest England. In addition to health protection and waterborne disease, his research interests include the public health response to violence. 
",What were the associated pathogens of concern?,"{'answer_start': [5228], 'text': ['Cryptosporidium oocysts']}"
8,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What type of samples were analyzed?
","{'answer_start': [1130], 'text': ['faecal sample']}"
18,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

",With what symptoms they were presented?,"{'answer_start': [2517], 'text': ['diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%)']}"
14,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

",What were the first steps of investigation?,"{'answer_start': [1369], 'text': ['A standardized questionnaire ']}"
9,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What is the initial cause of the event?
","{'answer_start': [5453], 'text': ['water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts']}"
34,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What is the date of the event?
","{'answer_start': [3], 'text': ['August 2003']}"
34,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What is the location of the event?
","{'answer_start': [121], 'text': ['southwest England.']}"
15,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","How was the event first detected?
","{'answer_start': [299], 'text': ['Following an earlier complaint from a visitor about the water quality']}"
34,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","How many people were ill?
","{'answer_start': [2332], 'text': ['Sixty three children (89%)']}"
17,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","How many people were hospitalized?
","{'answer_start': [2779], 'text': ['Ten children (16%)']}"
9,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What is the attack rate?
","{'answer_start': [4831], 'text': ['89% in the cohort studied']}"
12,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What are the pathogens?
","{'answer_start': [505], 'text': ['E.coli']}"
18,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What is the concentration of the contaminant after analysis?
","{'answer_start': [486], 'text': ['2100 coliforms, 40�E.coli�per cu mm']}"
28,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What are the symptoms?
","{'answer_start': [1010], 'text': ['diarrhoea, blood in stools, vomiting, nausea, or abdominal pain']}"
5,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What is the event?
","{'answer_start': [18], 'text': ['outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park']}"
21,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What are the initial steps of investigation?
","{'answer_start': [524], 'text': ['A cohort study']}"
5,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What type of samples were examined?
","{'answer_start': [2021], 'text': ['Faecal samples from the farmyard animals']}"
10,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","For which pathogens did they test for in the samples?
","{'answer_start': [1877], 'text': ['Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection']}"
27,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What measures were taken to prevent the event?
","{'answer_start': [5790], 'text': ['reviewed and revised health and safety risk assessments']}"
19,Contamination Question Answering,"In August 2003 an outbreak of cryptosporidiosis was identified in children who had recently visited an adventure park in southwest England. The adventure park contained a number of activities involving contact with water (boats, log flume, interactive water features) and contact with farm animals. Following an earlier complaint from a visitor about the water quality of one of the interactive water features designed for water play, water sampling had revealed a high coliform count (2100 coliforms, 40�E.coli�per cu mm). A cohort study was implemented to check whether there was any epidemiological evidence for a particular source within the adventure park.
Methods
The cohort population included all children (aged less than 16 years) among household members or friends of a probable or confirmed case who had visited the park with a case during August 2003. A probable case was defined as any child who had visited the park during August 2003 and who subsequently had gastrointestinal symptoms including diarrhoea, blood in stools, vomiting, nausea, or abdominal pain. A confirmed case was defined as a probable case with a faecal sample positive for cryptosporidium. Children who had travelled abroad in the two weeks before the onset of symptoms were excluded from the study.
Cases were identified from laboratory reports to the Health Protection Agency (HPA). A standardized questionnaire was administered over the telephone with an adult in the family of a case. Exposure data included water exposure (contact duration, type of contact, type of water source), animal contact and food consumption. Data were analysed using Epi Info 6.04 [7]. A univariable analysis was run to assess the association between exposures investigated and onset of disease. As only one variable showed an association and as the numbers were small, multivariable analysis was not performed.
Ten-liter grab samples were taken from the various water features within the park for cryptosporidium oocyst detection by South West Water Ltd. Faecal samples from the farmyard animals were also submitted. Oocysts were detected by light microscopy. Positive specimens were sent to the HPA Cryptosporidum Reference Laboratory for genotyping.
Results
Ninety one children were identified in the cohort, of whom 71 were contacted, giving a 78% response rate. Sixty three children (89%) met the case definition (27 confirmed and 36 probable cases). The sex distribution was even. Median age was 6 years (range 1-15). The most common symptom was diarrhoea (94%), followed by vomiting (64%), abdominal pain (62%), and nausea (51%). None of the children reported blood in stools. The median duration of illness was 8 days (range 1-18) and more than 30% of the children were still ill at the time of interview. Ten children (16%) required hospital admission.

Forty-six of the children who were cases (73%) had visited the park on 8 August, the date of symptom onset for the first case. Of the 51 children whose date of illness onset was known, 45 (88%) had a date of onset within one incubation period (1-10 days) of visiting the park [FIGURE].
Dates of onset were between 8 and 29 August, and the outbreak peaked on 13 and 14 August. For two of the four cases with date of onset more than 10 days after visiting the park, other household members had had gastrointestinal symptoms in the 10 days before onset. The two probable cases with onset date on date of visit became ill during the evening after leaving the adventure park.
The exposure yielding the strongest association with illness was contact with the interactive water feature [TABLE] (RR= 1.8, CI 95% 0.45 to 7.31, p=0.06). No specific type of contact with this source of water was significantly associated with illness. This feature involved being sprayed with recirculated water. Children often entered the feature fully clothed and with their shoes on. Nineteen children drank the recycled water and one parent reported that the water �smelt like drains�. The filtration and disinfection systems were not adequate to cope with high levels of contamination, and the water feature was closed on 21 August, soon after the start of this investigation.
Samples from 23 of the 27 confirmed cases were sent for genotyping. Sixteen yielded a result and 14 of these were�Cryptosporidium parvum�genotype 2. The initial sample from the interactive water feature contained a single oocyst that could not be genotyped. Although a subsequent sample from this feature when not in operation was positive and identified as�Cryptosporidium parvum�genotype 2, there was insufficient DNA for subtyping. Due to a failure of communication, faecal samples taken from animals resident in the park were not tested for cryptosporidium.
Discussion
This outbreak of cryptosporidiosis was characterised by a high attack rate (89% in the cohort studied), long duration of illness (median 8 days) and high proportion admitted to hospital (16%). The dates of onset were consistent with a common source of infection from an exposure in the adventure park. The analytical study showed an association between exposure to water in the interactive water feature and illness. Although the strength of the evidence was reduced due to the small numbers in the unexposed group, the finding was supported by the microbiological results and environmental observations. No association with other water sources or animal contact was detected. It seems likely that water in the interactive water feature became contaminated with faeces containing cryptosporidium oocysts, either from the footwear of users or from an unidentified primary case. These oocysts then continued to circulate in a viable condition as a result of ineffective filtration and disinfection.
In response to the outbreak, the park reviewed and revised health and safety risk assessments to manage and control the risk from protozoan parasites. The design of the water treatment and disinfection system was improved. The park also provided additional drinking fountains around the park and asked children to remove footwear before entering the interactive water feature. They improved signage, instructing visitors at all water-related attractions not to drink the water.

","What was the age of the affected people?
","{'answer_start': [2452], 'text': ['Median age was 6 years (range 1-15).']}"
30,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What type of samples were analyzed?
","{'answer_start': [7915], 'text': ['Fecal samples from patients']}"
15,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
",What were the first steps of investigation?,"{'answer_start': [363], 'text': ['epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources.']}"
23,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
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26,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
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16,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","How was the event first detected?
","{'answer_start': [25356], 'text': ['large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, ']}"
32,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
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34,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What are the pathogens?
","{'answer_start': [888], 'text': ['Cryptosporidium hominis oocysts ']}"
21,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [20456], 'text': ['150,000 oocysts/L and de- clined to 6200 oocysts/L']}"
18,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What are the symptoms?
","{'answer_start': [23325], 'text': ['fatigue, abdominal pain, upset stomach, and watery diarrhoea ']}"
28,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What is the concentration of the pathogen?
","{'answer_start': [20682], 'text': ['12,000 oocysts/L']}"
16,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
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","{'answer_start': [40], 'text': [' outbreak of cryptosporidiosis']}"
17,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What are the initial steps of investigation?
","{'answer_start': [495], 'text': ['a retrospective study based on phone calls to a health advice line ']}"
6,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What is the duration of the event?
","{'answer_start': [1086], 'text': ['The outbreak went unnoticed to authorities for several months.']}"
24,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
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","{'answer_start': [19603], 'text': ['Between 1 January and 1 July 2011']}"
31,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What are the first steps of mitigation?
","{'answer_start': [4495], 'text': ['A boil water notice (BWN)']}"
32,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What did they do to mitigate the event?
","{'answer_start': [4560], 'text': ['web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data']}"
23,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What type of samples were examined?
","{'answer_start': [953], 'text': ['patient and sewage samples,']}"
7,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What steps were taken to restore the problem?
","{'answer_start': [33849], 'text': ['the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started.']}"
22,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
","What was the age of the affected people?
","{'answer_start': [22721], 'text': ['children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1%']}"
12,Contamination Question Answering,"In the winter and spring of 2011 a large outbreak of cryptosporidiosis occurred in Skellefte municipality, Sweden. This study summarizes the outbreak investigation in terms of outbreak size, duration, clinical characteristics, possible source(s) and the potential for earlier detection using calls to a health advice line. Methods: The investigation included two epidemiological questionnaires and microbial analysis of samples from patients, water and other environmental sources. In addition, a retrospective study based on phone calls to a health advice line was performed by comparing patterns of phone calls between different water distribution areas. Results: Our analyses showed that approximately 18,500 individuals were affected by a waterborne outbreak of cryptosporidiosis in Skellefte in 2011. This makes it the second largest outbreak of cryptosporidiosis in Europe to date. Cryptosporidium hominis oocysts of subtype IbA10G2 were found in patient and sewage samples, but not in raw water or in drinking water, and the initial contamination source could not be determined. The outbreak went unnoticed to authorities for several months. The analysis of the calls to the health advice line provides strong indications early in the outbreak that it was linked to a particular water treatment plant. Conclusions: We conclude that an earlier detection of the outbreak by linking calls to a health advice line to water distribution areas could have limited the outbreak substantially. Keywords: Early outbreak detection, Cryptosporidiosis, Syndromic surveillance, Cryptosporidium hominis Background The protozoan parasite Cryptosporidium is a major cause of gastroenteritis in humans worldwide [1]. At least 29 valid species of Cryptosporidium have been identified [2] and the two most common species infecting humans are Crypto- sporidium parvum and Cryptosporidium hominis [3]. Cryptosporidium hominis has been the cause of several large waterborne outbreaks. The largest took place in 1993 in Milwaukee, USA, where more than 400,000 people were infected [4]. Cryptosporidiosis is mainly transmitted by the fecal-oral route, usually through oocyst-contaminated water or food, or through contact with infected humans or ani- mals. As few as 10 ingested oocysts can cause infection [5]. Asymptomatic carriage occurs [6, 7] while symptomatic in- fection is associated with diarrhoea, abdominal pain, nau- sea, vomiting and fever that usually resolve within 2 weeks. Symptoms occur a few days up to 2 weeks after ingestion of oocysts [5]. Severe life-threating diarrhoea may develop among immunocompromised patients [8]. Gastrointestinal- and joint symptoms can persist for several months after the initial infection with Cryptosporidium [9]. The public health impact of the parasite was recognised in Sweden in 2004 * Correspondence: par.bjelkmar@folkhalsomyndigheten.se 1Department of Monitoring and Evaluation, Public Health Agency of Sweden, 171 83 Solna, Sweden Full list of author information is available at the end of the article  The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bjelkmar et al. BMC Public Health  (2017) 17:328  DOI 10.1186/s12889-017-4233-8 when cryptosporidiosis became a notifiable disease and the parasite was also included in the World Health Organiza- tions Neglected Diseases Initiative in the same year [10]. In November and December 2010 a massive waterborne outbreak of C. hominis occurred in the city of stersund in Jmtland County, Sweden. Based on a retrospective cohort study, it was concluded that approximately 27,000 individ- uals were infected through the drinking water which made it the second biggest reported waterborne outbreak of cryptosporidiosis globally [11]. A couple of months later, in April 2011, drinking water from a municipal water treat- ment plant (WTP) in the neighboring county of Vsterbot- ten was suspected to be the source of a number of cases of cryptosporidiosis. A boil water notice (BWN) was therefore issued on 19 April and a web-based questionnaire was im- mediately created and published on the webpage of the mu- nicipality to collect epidemiological data. In order to complement the web-based questionnaire and better esti- mate the extent of the outbreak and to find its source, an additional study based on a postal questionnaire was per- formed in June 2011. The study was managed by the Vs- terbotten County Medical Office and the municipal environmental and health authorities in collaboration with the Public Health Agency of Sweden (at the time named Swedish Institute for Communicable Disease Control). Syndromic surveillance is defined as the real-time (or near real-time) collection, analysis, interpretation and dis- semination of health-related data [12]. As part of the on- going effort of development and evaluation of a syndromic surveillance system at the Public Health Agency, a retro- spective analysis of phone calls to a national health advice line from inhabitants living in Skellefte municipality dur- ing the time period of the outbreak was performed. No contemporaneous analysis of the phone calls was per- formed at the time of the outbreak. A new approach for early detection and improved situational awareness of local waterborne outbreaks was used where call patterns from individuals living in different drinking-water distribution areas were compared. The utility of syndromic surveillance systems for detecting and tracking local gastrointestinal outbreaks (GI) has been questioned [13] but systems based on data from health advice lines have been shown to be successful in a few cases [14, 15]. Globally, there are several examples of similar syndromic surveillance systems based on health advice lines [1618]. This study describes the outbreak investigation by sum- marizing the results from web-based and postal question- naires, human and environmental sampling and the analysis of phone calls to the health advice line. It outlines the extent and duration of the outbreak, risk factors and clinical characteristics of the infected persons, and discusses the potential for detecting the outbreak earlier. Figure 1 de- picts a time line indicating for which time periods the dif- ferent data sources were used in the analyses. Methods Study setting Skellefte is situated in Vsterbotten County geographic- ally located next to Jmtland County where the stersund outbreak occurred. The distance between Skellefte and stersund is almost 500 km. Skellefte is a municipality with a population of approximately 72,000 inhabitants. Twenty-eight water treatment plants are operating within the municipality. Two of these deliver water to the city of Skellefte; Slind WTP and Abborrverket WTP, where the latter delivers water to the majority of the inhabitants. All water treatment plants in the municipality use ground- water as the water source except Abborrverket which uses surface water obtained from the river Skelleftelven. Abborrverket WTP produces approximately 18,000 m3 of treated water daily to 44,000 of the 72,000 inhabitants in the municipality (31 March 2011). The normal water in- take to Abborrverket is located far out and deep in the river but due to icing during the winter months the intake is shifted to a more shallow position closer to shore where the ice can be removed more easily. Microbiological investigation Human samples Fecal samples from patients seeking healthcare for gastro- intestinal illness were analysed with standard techniques for enteric bacterial pathogens; polymerase chain reaction (PCR) for analysis of noro- and sapoviruses and micros- copy for analysis of Entamoeba spp. and Giardia intesti- nalis. Samples were only sporadically analysed for presence of Cryptosporidium oocysts up until 19 April 2011, when the current outbreak was first suspected. An intensification of testing for Cryptosporidium followed from that time until 1 July 2011 when the outbreak was considered over. Samples tested for Cryptosporidium were analysed using standard concentration technique followed by modified Ziehl-Neelsen staining [19]. A subset of posi- tive Cryptosporidium samples (n = 26) were sent to the Swedish Institute for Communicable Disease Control for species identification by PCR restriction fragment length polymorphism (RFLP) analysis of the rRNA gene [20, 21]. Subtypes were characterized by sequence analysis of the 60 kDa glycoprotein (gp60) gene [22, 23]. Environmental samples At the time of the outbreak Abborrverket WTP used floc- culation and sedimentation followed by sand filtering and chlorination for water treatment. This water treatment setup could be sufficient for removal of Cryptosporidium oocysts if the processes work optimally and the concentra- tion of oocysts is relatively low, but ultraviolet (UV) treat- ment is generally preferred as a disinfectant [24]. The winter intake was used from 19 November 2010 until 19 April 2011. A total of 38 samples were collected from the Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 2 of 10 drinking water system during a period of 5 months, 19 April to 15 September 2011. These samples included raw water from the river Skelleftelven, i.e. incoming water to Abborrverket WTP, treated water at Abborrverket WTP and samples taken from the distribution net. Twelve influent and twelve effluent wastewater samples were collected at the main sewage water treatment plant (SWTP) Tuvan. Moreover, in order to investigate possible causes of contamination of Skelleftelven and to trace sources of oocysts, 9 samples were collected from the wastewater and storm water systems and from other rele- vant locations. Water samples were analysed for Cryptosporidium oo- cysts according to ISO 15553:2006 [25] with filtration of water (101000 L), immunomagnetic separation (IMS) and immunofluorescence (IFL) microscopy. The slides with concentrated and purified material were identified by fluorescent-marked oocysts specific in size, shape, internal structure and DAPI-(4,6-diamidino-2-phenylindole)- stained nuclei. Wastewater samples were analyzed as water samples but without passing filters and in smaller volumes, 50100 mL for influent wastewater and 0.30.5 L for efflu- ent wastewater. Two sediment samples from the inside of the influent raw water pipe were also analysed as water sample but without filtration before IMS. DNA from one wastewater concentrate was analysed by sequence analysis of the gp60 gene as described for human samples [22, 23]. Epidemiological investigation Web-based questionnaire The same day as the BWN was issued, on 19 April 2011, a web-based questionnaire (Additional file 1) was created in order to immediately start collecting epidemiological data. The value of such a questionnaire was demonstrated in the preceding cryptosporidiosis outbreak in stersund [11] and those experiences were applied here as well. The questionnaire was made available to the public on the website of the municipality on the evening the same day, and was closed on 9 May 2011. The public was informed of the questionnaire by press releases and there were also links to it from key web pages such as the local newspaper and Vsterbotten County Council. The full data set was summarised after the outbreak was considered to be over. Visitors to the webpage who were residents of Skellefte municipality, both individuals with and without GI symp- toms, were asked to answer a set of questions regarding gastrointestinal illness in the family. A case attributed to the outbreak was defined as a person with residential ad- dress within Skellefte municipality with 3 loose stools per day for at least 1 day with onset between 1 April and 5 May 2011. Respondents with a date of symptom onset be- fore 1 April or after 5 May, persons who had travelled abroad 2 weeks prior to symptom onset, as well as individ- uals with a residential postal code outside Vsterbotten County were excluded from the analysis. Remaining re- spondents who did not fulfil the criteria of having 3 loose stools per day were considered non-cases. More detailed analyses of the data were not performed since the follow- up postal survey was conducted. Postal questionnaire A retrospective cohort study was performed in June 2011 by sending a questionnaire to a random sample of 1754 citizens in the municipality of Skellefte (Additional file 2, Additional file 3). The random sample was stratified by age (05 years, 615 years, 1665 years and 66 years or older) and gender. Questions were asked to find out about the start and magnitude of the outbreak, the source of the outbreak and risk factors for disease. The questionnaire contained questions on demographics, onset, duration and occurrence of symptoms indicating cryptosporidiosis, and water consumption as well as history of symptoms be- fore 1 January 2011. Caretakers were asked to answer for children <15 years of age. A case attributed to the out- break was defined as a person with 3 loose stools per day for at least 1 day with onset between 1 December 2010 and 31 May 2011. Statistical analysis of the postal questionnaire Each of the 1754 respondents were assigned a random number and a barcode on the questionnaire was used to identify each respondent. The postal codes were matched to the water distribution areas of the WTPs. In a stratified survey study, weights are used to calculate the number of individuals in the population represented by each individ- ual in the sample. Binary logistic regression was used to Fig. 1 Time line indicating for which time periods the different data sources were used in the analyses Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 3 of 10 find associated variables for the propensity of responding to the survey. Age, gender and water supply were used to calibrate the weights for non-response to adjust for unbal- ance between the sample and the population. The association between the binary outcome of case/ non-case and the exposure variables was analysed by binary logistic regression. Included in the model as covariates and exposure variables were gender, age (05 years, 615 years, 1665 years, and 66 years or older), gastric ulcer (yes, no), irritable bowel syndrome (yes, no), Crohns disease (yes, no), celiac disease (yes, no), lactose intolerance (yes, no), immunodeficiency disease (yes, no), average tap water con- sumption (<1 glass, 1 glass, 25 glasses, >5 glasses) and household water supply (Abborrverket, not Abborrverket or not from any WTP/own well). The results from the binary logistic regression were expressed as odds ratios (OR). All I do not know an- swers for binary questions were regarded as non- informative and were set as missing values prior to the analysis. Missing values for binary variables were then given a value (yes, no) using multiple imputation chain equations [26]. The chains contained all exposure vari- ables plus the outcome non-case/case [27]. Twenty data- sets with different imputed values for missing data were created and binary logistic regression results from each dataset were weighted together into one result using Rubins formula [28]. All analyses were performed in the statistical software R (version 3.3.2) using the packages survey (version 3.31.2), MICE (version 2.25) and the gen- eralized linear model function (glm) in the base R package stats. In all analyses a p-value less than 0.05 was used as a significant result and in case of estimated confidence in- tervals a confidence level of 95% was applied. Analysis of phone calls to a health advice line Healthcare Guide 1177 is a national Swedish telephone health advice line staffed by nurses. The service provides advice and information about urgent, but non-life- threatening, health problems. The medical record cre- ated for each consultation includes a structured data field, called the contact cause, that represents the most severe symptom as assessed by the nurse [29]. There are almost 200 contact causes in the services medical deci- sion support system but only a handful are related to GI problems. For the purpose of this study daily call counts on GI symptoms were retrospectively extracted from the service for inhabitants in Skellefte municipality from 1 August 2010 to 18 April 2011. The contact causes vomiting or nausea, diarrhoea and stomach pain were used since changes in contact patterns for these symptoms previously have been shown in outbreaks of cryptosporidiosis [14]. In addition, for each call, infor- mation on the postal code of the registered residence ad- dress of the patient was extracted. Postal codes were divided into two geographical regions; belonging to the distribution area of Abborrverket WPT or not, and the number of inhabitants in the corresponding regions were calculated. To compare the call patterns of GI-related symptoms between these two regions a previ- ously published outbreak detection algorithm [14] was used but with a minor modification. No analyses were performed for the period from the BWN and onwards since, as the in- formation of an ongoing outbreak becomes public, the con- tact pattern to the health advice line changes drastically and it is challenging to adjust for this in the analyses. The daily call count, Ct , i, for one contact cause or a sin- gle group of contact causes at day t for geographical re- gion i was classified as an outbreak signal if it exceeded a threshold Tt , i: Tt;i  max L; V  ; V  Et;i  L  SDt;i; L 3; 5 f g Et;i  pt;i  Ni; SDt;i   Ni  pt;i q  1pt;i; pt;i  Pni j1;ji P C;j 10  Pni j1;jiNj ;  t7; t8; t9; t10; t11; t12; t13; t14 f g;   2; if  t7; t14 f g 1; if  t8; t9; t10; t11; t12; t13 f g  where L is the threshold level for a weak and strong outbreak signal respectively, V is the threshold for a positive outbreak signal, Et , i is the expected number of calls and SDt , i is the standard deviation, both based on a binomial distribution, Niis the population size of geographical region i, pt , i is the probability of a single call per inhabitant per day, and ni is the number of geographical regions in the analysis. In the current study, two geographical regions were in- cluded: Abborrverket distribution area and not Abborrverket distribution area. It is important to note that calls from inhabitants of the geographical region under investigation are not included in the calculation of its threshold since that would increase the thresh- old if an outbreak in that region has been ongoing for more than 6 days. Compared to the previously published algorithm, the time period for the calcula- tion of pt , i has been modified. Here, calls for 8 days, t-7 to t-14, were included. Since the call patterns dif- fer between different weekdays, call counts for the weekdays matching the day for which the threshold is calculated, t-7 and t-14, has a weight of 2. The Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 4 of 10 motivation for this modification of the algorithm was primarily to reduce the risk of calculating pt , i based on small number of calls. Results Microbiological investigation Human samples Between 1 January and 1 July 2011, 145 laboratory con- firmed cases of domestic cryptosporidiosis were reported from Vsterbotten County. Only a handful were reported before 19 April, including one case on 15 April and two on 18 April. Genotyping identified C. hominis subtype IbA10G2 in samples from 24 confirmed cases, while no amplification product was obtained from the remaining two samples that were tested. No other gastrointestinal pathogens were found in a subset of the samples that were positive for Cryptosporidium. Environmental samples Cryptosporidium oocysts could not be detected in any of the 38 samples collected from the drinking water system. In influent and effluent wastewater samples from Tuvan SWTP oocysts were detected in 10 out of 24 samples. The concentration of oocysts in influent wastewater was highest on 22 April 2011 at 150,000 oocysts/L and de- clined to 6200 oocysts/L on 1 June 2011. From 27 June 2011 no oocysts were detected in influent wastewater. In effluent wastewater the concentration was highest on 8 June 2011 with a concentration of 12,000 oocysts/L. In subsequent samples the concentration varied between 1700 and 4200 oocysts/L and from 27 June 2011 the concentration was below the detection limit. Molecular investigation of one wastewater sample revealed C. hominis subtype IbA10G2. In the remaining 9 water and sediment samples collected at other places no oocysts were detected. Epidemiological investigation Web-based questionnaire The epidemiological curve based on the web-based questionnaire (Fig. 2) showed that the number of cases declined after a couple of days following the BWN and verified the hypothesis of an ongoing waterborne out- break. Importantly, it also indicated that the outbreak started well before 1 April. In total 12,358 individuals answered the questionnaire and 11,065 remained after exclusions. The results from the questionnaire were con- tinually monitored in order to provide information for decision making based on the extent of the outbreak, who were being affected and to follow up the effect of interventions. Moreover, it was used to inform the in- habitants about the progress of the outbreak and these reports were highly appreciated. Postal questionnaire In total, 1099 out of 1754 (63%) questionnaires were an- swered and returned for analysis. The survey showed that 26.4% of the respondents fulfilled the case defin- ition, i.e. self-reported diarrhoea (3 loose stools per day) between 1 December 2010 and 31 May 2011, which corresponds to an estimate of 18,449 cases (Table 1). The data from the survey also provided evidence that the outbreak started in January and ended by the end of May (Fig. 3). April was the peak month with 6969 cases. If the outbreak had been detected earlier and we assume that all cases from 1 February forward had remained healthy, the estimation is that the outbreak would have affected 2273 individuals, corresponding to approxi- mately 12% the current outbreak size. Only the variables age and water supply were identi- fied as risk factors for infection (Table 2). Divided into age groups, children up to 5 years were most affected, 37.2%, while the group of 66 years and above were least affected, 12.1% (Table 3). Among the different water supplies in Skellefte, water from Abborrverket WPT was the only supply that significantly correlated with an increased risk of infection (p < 0.001). Approximately 1 in 3 (32.7%) living in the distribution area of Abborrver- ket WPT had symptoms of cryptosporidiosis, compared to 16.2% of inhabitants living in other areas (Table 4). The most common symptoms, each present in more than 70% of the respondents that fulfilled the case defin- ition, were fatigue, abdominal pain, upset stomach, and watery diarrhoea (Table 5). Health advice line Starting on 30 December 2010, the retrospective analysis showed a sequence of 6 days of consecutive outbreak sig- nals regarding GI symptoms from individuals living in the distribution area of Abborrverket WTP (Fig. 4). Four of those were strong. A large number of outbreak signals for inhabitants living in the distribution area of Abborrverket WTP were evident during the following time period up until the BWN. In contrast, very few outbreak signals regarding GI symptoms were present for Abborrverket WPT distribu- tion area during the autumn and early winter of 2010. However, there was a small cluster of five outbreak signals between 20 November and 29 November 2010, but they were weak and not on consecutive days, hence the inter- pretation was that those outbreak signals were inconclu- sive. For the other geographical area in the analysis, individuals not living in the distribution area of Abborr- verket WTP, only one weak outbreak signal was present during the entire time-period under investigation - em- phasizing the abnormality of the identified outbreak signal pattern for the distribution area of Abborrverket WTP in the beginning of 2011. Similar results are obtained using Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 5 of 10 the original definition of the outbreak algorithm and with other groupings of ages and contact causes related to cryptosporidiosis (results not shown). When comparing the current outbreak signals based on geographical regions corresponding to the distribution of drinking water with outbreak signals based on (adult) GI calls from the entire Skellefte municipality with respect to the other municipalities within Vsterbotten County [14], the two patterns are similar and suggest the same time for outbreak detection: beginning of January 2011. Discussion The three cases of cryptosporidiosis in the middle of April together with other indications from informal sources re- garding large numbers of sick people, and higher-than- normal contacts regarding symptoms of gastrointestinal illness reported by the nurses staffing the regional health advice line, led the authorities to suspect an outbreak. However, our epidemiological investigation shows that the outbreak had already started, unnoticed to the authorities, in the beginning of January 2011. High norovirus activity together with only a handful of domestic cases of crypto- sporidiosis reported in Vsterbotten County between January and 19 April 2011 were contributing factors to the late detection of the outbreak. New routines are now in place in Vsterbotten County where analysis of Crypto- sporidium is performed on fecal samples if there are clus- ters of cases with gastrointestinal symptoms or other indications of an outbreak. If the outbreak had been detected in the beginning of the year by systematic monitoring of the telephone calls as described in this study, it is very likely that the outbreak would have ended during January. Two facts support this conclusion. First, once the outbreak was suspected the BWN was an effective intervention that substantially lim- ited illness within a few days. A similar delay in the Fig. 2 Epidemiological curve based on observed cases in the web questionnaire Table 1 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 Status N SE (N) 95% CI (N) N (%) Non-cases 51,618 1214 49,239  53,997 73.7 Cases 18,448 1191 16,114  20,782 26.3 N Number, SE standard error, CI confidence interval Based on postal questionnaire Fig. 3 Epidemiological curve of population estimates of number of cases from the postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 6 of 10 decrease of reported cases was seen in the stersund out- break [11] and it is explained by the time it takes to de- velop symptoms after ingestion of oocyst. Second, the outbreak signals from the described analyses of telephone calls would have given a strong indication during January that the outbreak was waterborne and which drinking water supply to suspect (Abborrverket WTP). We therefor argue that such an early outbreak detection followed by a timelier BWN in January 2011 would have limited the out- break substantially  from approximately 18,500 cases down to 2300 cases if all who fell ill after 31 January had remained healthy. The potential of syndromic surveillance systems based on analysing telephone call patterns to Healthcare Guide 1177 for early event detection and situational awareness of local outbreaks has been shown previously [14]. In the current work the concept was taken a step further by comparing call patterns between water distribution areas that were based on groups of postal codes. The im- portance of this should not be underestimated. In the situation of an unknown waterborne outbreak, or other types of local outbreaks where the spread matches geographical areas used in the analysis, this procedure gives a more timely indication of the underlying cause and therefore substantially increases the chances of ef- fective countermeasures. Since water distribution areas are known, the approach can be used in systems for syn- dromic surveillance. There is always a tradeoff between sensitivity and spe- cificity in signal detection. In practical terms it is the in- stitution that is eligible to act on the signal that needs to find a reasonable protocol for signal evaluation and val- idation. To increase the sensitivity and hence the poten- tial of timely detection of local outbreaks, which usually are very short-lived in contrast to the outbreak under in- vestigation here, the outbreak algorithm used operates on a daily basis. This has the drawback of reduced speci- ficity, i.e. that more false positive outbreak signals are generated due to randomness, especially for geographical regions where the population size is small. Despite this, and even though the daily call counts are relatively low, the outbreak signal pattern shown in Fig. 4 is excep- tional and clearly indicates that individuals living in the distribution area of Abborrverket WTP report more GI symptoms compared to individuals living in other areas. Moreover, this outbreak signal pattern is similar if other groupings of age and contact causes related to symptoms of cryptosporidiosis are used. Although possible sources of contamination were in- vestigated and discussed no conclusive information could be found. Several samples from the drinking water system and the environment were analysed for Crypto- sporidium oocysts but none were detected - apart from the findings in wastewater samples. The most likely the- ory in our opinion is that the winter intake of water to Abborrverket WTP, which is more exposed to contamin- ation since it is located more shallowly in the river and closer to shore compared to the summer intake, was contaminated with Cryptosporidium oocysts from sew- age from one or several sources. However, data on weekly maximal turbidity and bacteriological counts (Escherichia coli, general coliform bacteria, enterococci and Clostridium perfringens) in raw water to Abborrver- ket WTP for the period October 2010 to March 2011 had been within normal levels so such a contamination, if present, was not detected in the routine testing at the WTP. The water intake was shifted to the summer position on the same day as the BWN was issued on 19 April 2011, which may explain why no Cryptosporidium oo- cysts were found in the water samples, since they were all taken after 19 April. It is worth noting that the out- break signals from the syndromic surveillance algorithm present in November 2010 coincide with the shift to the winter intake which might indicate a contamination at that point in time as well - although probably unrelated Table 2 Significant risk factors for infection based on postal questionnaire Odds ratio 95% CI P-value* Age 0-5 4.22 2.66  6.68 <0.001 6-15 2.28 1.42  3.68 0.001 16-65 3.08 1.96  4.83 <0.001 66- 1.00 Water source Not from any WTP/own well 1.00 Abborrverket WTP 2.30 1.49  3.56 <0.001 Not Abborrverket WTP 1.14 0.68  1.91 0.613 CI confidence interval, WTP water treatment plant *Fishers exact P - value Table 3 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into age groups Status Age N SE (N) 95% CI (N) N (%) Non-cases 0-5 2433 121 2195  2671 62.8 6-15 5542 208 5135  5950 75.3 16-65 30,728 1148 28,479  32,977 69.6 66- 12,914 326 12,276  13,553 87.9 Cases 0-5 1442 120 1207  1676 37.2 6-15 1819 202 1423  2215 24.7 16-65 13,402 1132 11,183  15,621 30.4 66- 1786 301 1196  2377 12.1 N number, SE standard error; CI confidence interval Based on postal questionnaire Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 7 of 10 to the current outbreak. The fact that Cryptosporidium oocysts were found in wastewater is in our opinion re- lated to the fact that a substantial part of the population connected to the municipal SWTP Tuvan was infected with C. hominis IbA10G2. Thus, although the initial cause of the outbreak remains unknown, it was most certainly caused by fecal contamination of human origin since C. hominis is almost exclusively human specific. Compared to the stersund outbreak [11] only age was the common risk factor. In contrast, the current study did not find statistical significance for any of the underlying diseases nor amount of water consumed. Symptom pro- files were almost identical between the outbreaks. The same Cryptosporidium gp60 subtype was found respon- sible for both the current and the stersund outbreak. It is in our opinion likely that the outbreaks were related since this subtype seldom is found in domestic cases in Sweden, in contrast to other European countries, and the time period between the outbreaks was short. However, similarity on gp60 is not conclusive evidence [30] and the question of whether two outbreaks were related is currently investigated by whole genome sequencing. Speculatively, one or a few infected individuals from the stersund outbreak brought the parasite to Skellefte and caused a second outbreak through spread of Cryptosporid- ium oocysts via sewage, into the river, finally ending up in the drinking water since the microbial barriers present in Abborrverket WPT at the time were insufficient to inacti- vate or remove the oocysts. After the outbreak was identified, the water distribution system was flushed to remove the contamination and work to improve the water treatment in Abborrverket WTP was started. Since the large outbreak in stersund only took place a few months earlier the municipality of Skellefte could utilize experience from the actions taken to stop the former outbreak. Even so, the BWN had to be kept in place for 5 months, compared to 3 months in stersund. This was partly due to the longer period of time it took to install an ultraviolet unit as an additional Table 4 Population estimates of cases and non-cases of Cryptosporidium-infection in Skellefte between December 2010 and May 2011 divided into water supply categories Status Category N SE (N) 95% CI (N) N (%) Non-cases Not Abborrverket WTP 22,649 642 21,392  23,906 83.8 Abborrverket WTP 28,696 1033 26,944  30,994 67.3 Cases Not Abborrverket WTP 4368 624 3145  5590 16.2 Abborrverket WTP 14,081 1019 12,084  16,078 32.7 N number, SE standard error, CI confidence interval Based on postal questionnaire Table 5 Clinical features of Cryptosporidium-infection cases in the municipality of Skellefte during December 2010 to May 2011 Proportion with symptom (%) 95% CI (%) Fatigue 78.5 72.4  84.7 Abdominal pain 73.3 66.8  79.8 Upset stomach 71.4 64.7  78.2 Diarrhoea Watery 70.2 63.4  77.0 Bloody 0.9 0.0  2.5 Nausea 63.5 56.1  70.9 Headache 46.9 39.3  54.5 Vomiting 35.8 28.6  43.1 Fever >38 C 36.5 28.2  42.8 Joint pain 27.4 20.4  34.4 Pain in eyes 14.6 9.1  20.1 CI confidence interval Based on postal questionnaire Fig. 4 Daily call counts from Skellefte municipality to Healthcare Guide 1177 regarding GI symptoms from 1 August 2010 until the day before the BWN on 19 April 2011. Inhabitants are divided into two groups; those living in the water distribution area of Abborrverket WPT (blue) and those who are not (red). Outbreak signals from the detection algorithm [14] are shown as blue (Abborrverket WTP) and red circles (not Abborrverket WTP) with weak (hollow circles) and strong outbreak signals (filled circles) along the lower horizontal and upper horizontal, respectively Bjelkmar et al. BMC Public Health  (2017) 17:328  Page 8 of 10 microbiological barrier in Abborrverket WTP as well as a longer and more complex water distribution network that had to be flushed. As of November 2016, the municipality of Skellefte is in the process of rebuilding their infrastruc- ture for production of drinking water. This work had started before the outbreak of cryptosporidiosis. Conclusions Our investigation concludes that approximately 18,500 people in the municipality of Skellefte were infected by Cryptosporidium during the winter and spring of 2011 making it the second largest outbreak of cryptosporidiosis described in Europe to date. Cryptosporidium hominis subtype IbA10G2 was isolated from patient samples and wastewater. The epidemiological investigation strongly indicates that this outbreak was waterborne based on the vast number of cases, as well as the fact that the BWN were an effective countermeasure, and that people living in the water distribution area of one specific WTP were more likely to become ill. This conclusion is also strongly supported by the pattern of phone calls to the national health advice line Healthcare Guide 1177. We therefore firmly believe that the outbreak was waterborne and caused by C. hominis transmitted through the public water supplied by Abborrverket WTP even though no oocysts could be found in raw water or in drinking water. Moreover, our results show that the outbreak went unnoticed to the authorities for several months and that systematic monitoring of phone calls to the health advice line, as described in this study, could have limited the out- break to approximately 2300 cases compared to the current estimate of 18,500 cases. This new approach of linking health advice line calls to water distribution areas has been implemented in a system for syndromic surveillance deployed by the Public Health Agency of Sweden in 2016. Additional files Additional file 1: Web-based questionnaire. Translated web-based questionnaire. (PDF 162 kb) Additional file 2: Postal questionnaire for adults. Translated postal questionnaire for adults. (PDF 128 kb) Additional file 3: Postal questionnaire for children. Translated postal questionnaire for children. (PDF 128 kb) Abbreviations BWN: Boil water notice; GI: Gastrointestinal; IFL: Immunofluorescence; IMS: Immunomagnetic separation; OR: Odds ratio; PCR: Polymerase chain reaction; RFLP: Fragment length polymorphism; SWTP: Sewage water treatment plan; UV: Ultraviolet; WTP: Water treatment plant Acknowledgements The authors would like to thank Leah Martin at the Public Health Agency of Sweden for useful comments on the manuscript and Stefan Johansson of Skellefte municipality for the information on the drinking water infrastructure, production and testing. Funding The study was partly funded by the Swedish Agency for Contingency Planning through a research and development project named Event-based Surveillance System (ESS). The funding organisation was not involved in any part of the study. Availability of data and materials The datasets used are available from the corresponding author on request. Authors contributions PB conceived and performed the health advice line study and wrote the manuscript. AH performed water analysis and was part of the outbreak team. JB designed and made the statistical analyses of the epidemiology part of the manuscript. ML was part of the outbreak team. ML performed analysis on human samples, including typing and sub-typing and was part of the outbreak team. GA performed water analysis and was part of the outbreak team. SS was responsible for the local outbreak team and contributed to the study design and acquisition of data. JL conceived the study and performed epidemiological analysis. All authors contributed to the interpretation of data and made substantial contributions to the overall content of the manuscript, and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Consent for publication Not applicable. Ethics approval and consent to participate The study was approved by Stockholm ethical review board, reference number 2011/220-31/4. Written informed consent was not necessary due to outbreak investigation. However, a letter stating the art of the investigation was handed out to all participants. Here it was also stated that all personal identification issues were handled according to Swedish law. Furthermore, answers to questionnaires would be seen as written consent to participate in study. Collection of field samples The field samples were collected as part of an ongoing outbreak investigation, followed Swedish routines and legislation, and the sampling was performed in collaboration with local authorities and the drinking water producer. Requirement for permission was waived. Publishers Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. 
",What is the source of contamination?,"{'answer_start': [4338], 'text': ['municipal water treat- ment plant (WTP) ']}"
15,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What type of samples were analyzed?
","{'answer_start': [241], 'text': ['faecal specimens']}"
10,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
",What symptoms did people report?,"{'answer_start': [3085], 'text': ['diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting']}"
19,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What is the date of the event?
","{'answer_start': [1172], 'text': ['2006']}"
15,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What is the location of the event?
","{'answer_start': [102], 'text': ['New Zealand']}"
21,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
",What pathogen was connected to the outbreak?,"{'answer_start': [1281], 'text': ['C. parvum']}"
21,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What is the source that started the event?
","{'answer_start': [3470], 'text': ['direct zoonotic transfer through contact with calves']}"
28,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","How many people were ill?
","{'answer_start': [2632], 'text': ['25/80 cases']}"
28,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What is the attack rate?
","{'answer_start': [2669], 'text': ['31%']}"
30,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What are the pathogens?
","{'answer_start': [174], 'text': ['Cryptosporidium parvum']}"
13,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What are the symptoms?
","{'answer_start': [769], 'text': ['abdominal discomfort, diarrhoea, and in some cases, vomiting']}"
19,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What is the event?
","{'answer_start': [1197], 'text': ['outbreak of gastrointestinal illness in a class of 96 veterinary students']}"
22,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
","What type of samples were examined?
","{'answer_start': [1371], 'text': ['water sample']}"
26,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
",What is the source of contamination?,"{'answer_start': [451], 'text': ['contact with calves ']}"
13,Contamination Question Answering,"The occurrence of a gastrointestinal illness among a class of 96 undergraduate veterinary students in New Zealand prompted laboratory and questionnaire-based investigations. Cryptosporidium parvum was the only enteropathogen identied in 4/7 faecal specimens analysed. The C. parvum isolates carried a rare IIa GP60 allele, indicating a point-source outbreak. The infection source could not be microbiologically traced, but the investigation suggested contact with calves during a practical class as the most likely exposure. The inferred median incubation period was 5 days (range 011 days), and the median illness duration was 56 days (range 223 days), corroborating previous observations in experimental cryptosporidiosis. Disease was self-limiting, characterized by abdominal discomfort, diarrhoea, and in some cases, vomiting. Originating from a rural area and having had previously handled ruminants were associated with a signicant risk reduction in males. All the three students who reported chronic use of steroid inhalers for treatment of asthma were cases. This case highlighted, once again, the potential hazard for explosive outbreaks of cryptosporidiosis. In 2006, we investigated an outbreak of gastrointestinal illness in a class of 96 veterinary students, in which C. parvum was identified as the sole enteropathogen in multiple faecal specimens. A 100-l water sample was collected from one of the drinking water taps on the same day of the investigation and filtered on-site using a commercial filter (FiltaMax, Idexx Laboratories, USA), at a ow rate of 2 l/min. A 200-ml sample was also collected in a sterile bottle, placed on ice and transported to an environmental microbiology laboratory for analysis for the presence of Escherichia coli bacteria. The same day, the dairy farm that provided the calves for the practical class was visited. The farm was situated about 5 km from LATU. Faecal specimens from nine calves aged >30 days were submitted on ice to IVABS Unfortunately, the calves actually used in the class had been sold and could not be traced, and other calves aged <1 month were not present at the day of the visit as the calving season had ended. Seven faecal specimens submitted by students were analysed for the presence of enteropathogens. The three specimens initially analysed at the regional diagnostic laboratory tested negative for Campylobacter and one tested positive for Cryptosporidium. All the seven specimens submitted to IVABS tested negative for rotavirus, Salmonella spp., norovirus and Giardia, and four tested positive for Cryptosporidium oocysts by immunouorescence. There were 25/80 cases among respondents to Q1 (31% attack rate), and 15/64 among respondents to Q2 (P=0.35). Nine out of 25 cases (36%) sought medical advice during the course of the illness. All 64 respondents to Q2 had attended the calf-handling practical (Table 2), and none of them responded as having drunk tap water at LATU during the same practical, arguing against a water-borne source of infection there (Table 2). Sixteen out of 25 cases (64%) reported diarrhoea and abdominal discomfort in Q1; six (24%) abdominal discomfort, diarrhoea, and vomiting; two (8%) abdominal discomfort only, and one (4%) vomiting only. Although a single negative water sample was of limited value to completely rule out a water-borne outbreak of cryptosporidiosis, Q2 indicated none of the respondents had drunk tap water during the practical class, leaving direct zoonotic transfer through contact with calves as the most likely route of transmission. An attack rate of 31% was estimated based on the responses to Q1. 
",What were the associated pathogens of concern?,"{'answer_start': [2416], 'text': ['Cryptosporidium']}"
17,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. 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Novel microbiological and spatial statistical  methods to improve strength of epidemiological evidence  in a community-wide waterborne outbreak. PLoS One.  2014;9(8):e104713. DOI: 10.1371/journal.pone.0104713 PMID:  25147923 18. Kauppinen A, Ikonen J, Pursiainen A, Pitknen T, Miettinen  IT. Decontamination of a drinking water pipeline system  contaminated with adenovirus and Escherichia coli utilizing  peracetic acid and chlorine.J Water Health. 2012;10(3):406-18.  DOI: 10.2166/wh.2012.003 PMID: 22960485 19. Kauppinen A, Martikainen K, Matikka V, Veijalainen A-M,  Pitknen T, Heinonen-Tanski H,  et al.  Sand filters for removal  of microbes and nutrients from wastewater during a one-year  pilot study in a cold temperate climate. J Environ Manage.  2014;133:206-13. DOI: 10.1016/j.jenvman.2013.12.008 PMID:  24384282 8 www.eurosurveillance.org 20. International Organization for Standardization (ISO). ISO/TS  15216-1. Microbiology of food and animal feed - Horizontal  method for determination of hepatitis A virus and norovirus in  food using real-time RT-PCR - Part 1: Method for quantification.  Geneva: ISO; 2013. Available from: http://www.iso.org/iso/ catalogue_detail.htm?csnumber=55382 21. International Organization for Standardization (ISO). ISO 9308- 2. Water quality -- Enumeration of Escherichia coli and coliform  bacteria -- Part 2: Most probable number method. Geneva: ISO;  2012. Available from: http://www.iso.org/iso/iso_catalogue/ catalogue_tc/catalogue_detail.htm?csnumber=52246 22. International Organization for Standardization (ISO). ISO 7899- 2. Water quality -- Detection and enumeration of intestinal  enterococci -- Part 2: Membrane filtration method. Geneva:  ISO; 2000. Geneva, Switzerland. Available from: http://www. iso.org/iso/catalogue_detail.htm?csnumber=14854 23. Rnnqvist M, Rtt M, Tuominen P, Salo S, Maunula L.  Swabs as a tool for monitoring the presence of norovirus  on environmental surfaces in the food industry.J Food Prot.  2013;76(8):1421-8. DOI: 10.4315/0362-028X.JFP-12-371 PMID:  23905799 24. Jothikumar N, Cromeans TL, Hill VR, Lu X, Sobsey MD, Erdman  DD. Quantitative real-time PCR assays for detection of  human adenoviruses and identification of serotypes 40 and  41.Appl Environ Microbiol. 2005;71(6):3131-6. DOI: 10.1128/ AEM.71.6.3131-3136.2005 PMID: 15933012 25. An exceptionally long heatwave. Press release. Helsinki:  Finnish Meteorological Institute; 15 Aug 2014. Available from:  http://en.ilmatieteenlaitos.fi/press-release/10014539 26. Schets FM, De Roda Husman AM, Havelaar AH. Disease  outbreaks associated with untreated recreational water  use.Epidemiol Infect. 2011;139(7):1114-25. DOI: 10.1017/ S0950268810002347 PMID: 21062530 27. Temperature and precipitation statistics from 1961 onwards.  Helsinki: Finnish Meteorological Institute. [Accessed: 23  Aug 2016]. Available from: http://en.ilmatieteenlaitos.fi/ statistics-from-1961-onwards 28. Atmar RL, Opekun AR, Gilger MA, Estes MK, Crawford SE, Neill  FH,  et al.  Norwalk virus shedding after experimental human  infection. Emerg Infect Dis. 2008;14(10):1553-7. DOI: 10.3201/ eid1410.080117 PMID: 18826818 29. Teunis PF, Moe CL, Liu P, Miller SE, Lindesmith L, Baric  RS,  et al.  Norwalk virus: how infectious is it? J Med Virol.  2008;80(8):1468-76. DOI: 10.1002/jmv.21237 PMID: 18551613 30. Dufour AP, Evans O, Behymer TD, Cant R. Water ingestion  during swimming activities in a pool: a pilot study.J Water  Health. 2006;4(4):425-30.PMID: 17176813 31. Robilotti E, Deresinski S, Pinsky BA. Norovirus.Clin Microbiol  Rev. 2015;28(1):134-64. DOI: 10.1128/CMR.00075-14 PMID:  25567225 32. Prez-Sautu U, Sano D, Guix S, Kasimir G, Pint RM, Bosch A.  Human norovirus occurrence and diversity in the Llobregat  river catchment, Spain.Environ Microbiol. 2012;14(2):494-502.  DOI: 10.1111/j.1462-2920.2011.02642.x PMID: 22118046 33. Lysn M, Thorhagen M, Brytting M, Hjertqvist M, Andersson  Y, Hedlund KO. Genetic diversity among food-borne and  waterborne norovirus strains causing outbreaks in Sweden.J  Clin Microbiol. 2009;47(8):2411-8. DOI: 10.1128/JCM.02168-08  PMID: 19494060 34. Vega E, Barclay L, Gregoricus N, Shirley SH, Lee D, Vinj J.  Genotypic and epidemiologic trends of norovirus outbreaks  in the United States, 2009 to 2013.J Clin Microbiol.  2014;52(1):147-55. DOI: 10.1128/JCM.02680-13 PMID: 24172151 35. Enriquez CE, Hurst CJ, Gerba CP. Survival of the enteric  adenoviruses 40 and 41 in tap, sea, and waste water.Water  Res. 1995;29(11):2548-53. DOI: 10.1016/0043-1354(95)00070-2 36. Pina S, Puig M, Lucena F, Jofre J, Girones R. Viral pollution in  the environment and in shellfish: human adenovirus detection  by PCR as an index of human viruses.Appl Environ Microbiol.  1998;64(9):3376-82.PMID: 9726885 37. Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What is the initial cause of the event?
","{'answer_start': [359], 'text': ['bathing water']}"
23,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Novel microbiological and spatial statistical  methods to improve strength of epidemiological evidence  in a community-wide waterborne outbreak. PLoS One.  2014;9(8):e104713. DOI: 10.1371/journal.pone.0104713 PMID:  25147923 18. Kauppinen A, Ikonen J, Pursiainen A, Pitknen T, Miettinen  IT. Decontamination of a drinking water pipeline system  contaminated with adenovirus and Escherichia coli utilizing  peracetic acid and chlorine.J Water Health. 2012;10(3):406-18.  DOI: 10.2166/wh.2012.003 PMID: 22960485 19. Kauppinen A, Martikainen K, Matikka V, Veijalainen A-M,  Pitknen T, Heinonen-Tanski H,  et al.  Sand filters for removal  of microbes and nutrients from wastewater during a one-year  pilot study in a cold temperate climate. J Environ Manage.  2014;133:206-13. DOI: 10.1016/j.jenvman.2013.12.008 PMID:  24384282 8 www.eurosurveillance.org 20. International Organization for Standardization (ISO). ISO/TS  15216-1. Microbiology of food and animal feed - Horizontal  method for determination of hepatitis A virus and norovirus in  food using real-time RT-PCR - Part 1: Method for quantification.  Geneva: ISO; 2013. Available from: http://www.iso.org/iso/ catalogue_detail.htm?csnumber=55382 21. International Organization for Standardization (ISO). ISO 9308- 2. Water quality -- Enumeration of Escherichia coli and coliform  bacteria -- Part 2: Most probable number method. Geneva: ISO;  2012. Available from: http://www.iso.org/iso/iso_catalogue/ catalogue_tc/catalogue_detail.htm?csnumber=52246 22. International Organization for Standardization (ISO). ISO 7899- 2. Water quality -- Detection and enumeration of intestinal  enterococci -- Part 2: Membrane filtration method. Geneva:  ISO; 2000. Geneva, Switzerland. Available from: http://www. iso.org/iso/catalogue_detail.htm?csnumber=14854 23. Rnnqvist M, Rtt M, Tuominen P, Salo S, Maunula L.  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A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What is the date of the event?
","{'answer_start': [165], 'text': ['July and August 2014']}"
16,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  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Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What is the location of the event?
","{'answer_start': [7453], 'text': ['Finland']}"
27,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. 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Swabs as a tool for monitoring the presence of norovirus  on environmental surfaces in the food industry.J Food Prot.  2013;76(8):1421-8. DOI: 10.4315/0362-028X.JFP-12-371 PMID:  23905799 24. Jothikumar N, Cromeans TL, Hill VR, Lu X, Sobsey MD, Erdman  DD. Quantitative real-time PCR assays for detection of  human adenoviruses and identification of serotypes 40 and  41.Appl Environ Microbiol. 2005;71(6):3131-6. DOI: 10.1128/ AEM.71.6.3131-3136.2005 PMID: 15933012 25. An exceptionally long heatwave. Press release. Helsinki:  Finnish Meteorological Institute; 15 Aug 2014. Available from:  http://en.ilmatieteenlaitos.fi/press-release/10014539 26. Schets FM, De Roda Husman AM, Havelaar AH. Disease  outbreaks associated with untreated recreational water  use.Epidemiol Infect. 2011;139(7):1114-25. DOI: 10.1017/ S0950268810002347 PMID: 21062530 27. Temperature and precipitation statistics from 1961 onwards.  Helsinki: Finnish Meteorological Institute. [Accessed: 23  Aug 2016]. 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Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
",What pathogen was connected to the outbreak?,"{'answer_start': [567], 'text': ['noroviruses']}"
24,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Novel microbiological and spatial statistical  methods to improve strength of epidemiological evidence  in a community-wide waterborne outbreak. PLoS One.  2014;9(8):e104713. DOI: 10.1371/journal.pone.0104713 PMID:  25147923 18. Kauppinen A, Ikonen J, Pursiainen A, Pitknen T, Miettinen  IT. Decontamination of a drinking water pipeline system  contaminated with adenovirus and Escherichia coli utilizing  peracetic acid and chlorine.J Water Health. 2012;10(3):406-18.  DOI: 10.2166/wh.2012.003 PMID: 22960485 19. Kauppinen A, Martikainen K, Matikka V, Veijalainen A-M,  Pitknen T, Heinonen-Tanski H,  et al.  Sand filters for removal  of microbes and nutrients from wastewater during a one-year  pilot study in a cold temperate climate. J Environ Manage.  2014;133:206-13. DOI: 10.1016/j.jenvman.2013.12.008 PMID:  24384282 8 www.eurosurveillance.org 20. International Organization for Standardization (ISO). ISO/TS  15216-1. Microbiology of food and animal feed - Horizontal  method for determination of hepatitis A virus and norovirus in  food using real-time RT-PCR - Part 1: Method for quantification.  Geneva: ISO; 2013. Available from: http://www.iso.org/iso/ catalogue_detail.htm?csnumber=55382 21. International Organization for Standardization (ISO). ISO 9308- 2. Water quality -- Enumeration of Escherichia coli and coliform  bacteria -- Part 2: Most probable number method. Geneva: ISO;  2012. Available from: http://www.iso.org/iso/iso_catalogue/ catalogue_tc/catalogue_detail.htm?csnumber=52246 22. International Organization for Standardization (ISO). ISO 7899- 2. Water quality -- Detection and enumeration of intestinal  enterococci -- Part 2: Membrane filtration method. Geneva:  ISO; 2000. Geneva, Switzerland. Available from: http://www. iso.org/iso/catalogue_detail.htm?csnumber=14854 23. Rnnqvist M, Rtt M, Tuominen P, Salo S, Maunula L.  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Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","How was the event first detected?
","{'answer_start': [1513], 'text': ['via the media']}"
27,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  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Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","How many people were ill?
","{'answer_start': [468], 'text': ['1,453']}"
16,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. 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Swabs as a tool for monitoring the presence of norovirus  on environmental surfaces in the food industry.J Food Prot.  2013;76(8):1421-8. DOI: 10.4315/0362-028X.JFP-12-371 PMID:  23905799 24. Jothikumar N, Cromeans TL, Hill VR, Lu X, Sobsey MD, Erdman  DD. Quantitative real-time PCR assays for detection of  human adenoviruses and identification of serotypes 40 and  41.Appl Environ Microbiol. 2005;71(6):3131-6. DOI: 10.1128/ AEM.71.6.3131-3136.2005 PMID: 15933012 25. An exceptionally long heatwave. Press release. Helsinki:  Finnish Meteorological Institute; 15 Aug 2014. Available from:  http://en.ilmatieteenlaitos.fi/press-release/10014539 26. Schets FM, De Roda Husman AM, Havelaar AH. Disease  outbreaks associated with untreated recreational water  use.Epidemiol Infect. 2011;139(7):1114-25. DOI: 10.1017/ S0950268810002347 PMID: 21062530 27. Temperature and precipitation statistics from 1961 onwards.  Helsinki: Finnish Meteorological Institute. [Accessed: 23  Aug 2016]. Available from: http://en.ilmatieteenlaitos.fi/ statistics-from-1961-onwards 28. Atmar RL, Opekun AR, Gilger MA, Estes MK, Crawford SE, Neill  FH,  et al.  Norwalk virus shedding after experimental human  infection. Emerg Infect Dis. 2008;14(10):1553-7. DOI: 10.3201/ eid1410.080117 PMID: 18826818 29. Teunis PF, Moe CL, Liu P, Miller SE, Lindesmith L, Baric  RS,  et al.  Norwalk virus: how infectious is it? J Med Virol.  2008;80(8):1468-76. DOI: 10.1002/jmv.21237 PMID: 18551613 30. Dufour AP, Evans O, Behymer TD, Cant R. Water ingestion  during swimming activities in a pool: a pilot study.J Water  Health. 2006;4(4):425-30.PMID: 17176813 31. Robilotti E, Deresinski S, Pinsky BA. Norovirus.Clin Microbiol  Rev. 2015;28(1):134-64. DOI: 10.1128/CMR.00075-14 PMID:  25567225 32. Prez-Sautu U, Sano D, Guix S, Kasimir G, Pint RM, Bosch A.  Human norovirus occurrence and diversity in the Llobregat  river catchment, Spain.Environ Microbiol. 2012;14(2):494-502.  DOI: 10.1111/j.1462-2920.2011.02642.x PMID: 22118046 33. Lysn M, Thorhagen M, Brytting M, Hjertqvist M, Andersson  Y, Hedlund KO. Genetic diversity among food-borne and  waterborne norovirus strains causing outbreaks in Sweden.J  Clin Microbiol. 2009;47(8):2411-8. DOI: 10.1128/JCM.02168-08  PMID: 19494060 34. Vega E, Barclay L, Gregoricus N, Shirley SH, Lee D, Vinj J.  Genotypic and epidemiologic trends of norovirus outbreaks  in the United States, 2009 to 2013.J Clin Microbiol.  2014;52(1):147-55. DOI: 10.1128/JCM.02680-13 PMID: 24172151 35. Enriquez CE, Hurst CJ, Gerba CP. Survival of the enteric  adenoviruses 40 and 41 in tap, sea, and waste water.Water  Res. 1995;29(11):2548-53. DOI: 10.1016/0043-1354(95)00070-2 36. Pina S, Puig M, Lucena F, Jofre J, Girones R. Viral pollution in  the environment and in shellfish: human adenovirus detection  by PCR as an index of human viruses.Appl Environ Microbiol.  1998;64(9):3376-82.PMID: 9726885 37. Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What are the pathogens?
","{'answer_start': [955], 'text': ['faecal indicator  bacteria']}"
26,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Novel microbiological and spatial statistical  methods to improve strength of epidemiological evidence  in a community-wide waterborne outbreak. PLoS One.  2014;9(8):e104713. DOI: 10.1371/journal.pone.0104713 PMID:  25147923 18. Kauppinen A, Ikonen J, Pursiainen A, Pitknen T, Miettinen  IT. Decontamination of a drinking water pipeline system  contaminated with adenovirus and Escherichia coli utilizing  peracetic acid and chlorine.J Water Health. 2012;10(3):406-18.  DOI: 10.2166/wh.2012.003 PMID: 22960485 19. Kauppinen A, Martikainen K, Matikka V, Veijalainen A-M,  Pitknen T, Heinonen-Tanski H,  et al.  Sand filters for removal  of microbes and nutrients from wastewater during a one-year  pilot study in a cold temperate climate. J Environ Manage.  2014;133:206-13. DOI: 10.1016/j.jenvman.2013.12.008 PMID:  24384282 8 www.eurosurveillance.org 20. International Organization for Standardization (ISO). ISO/TS  15216-1. Microbiology of food and animal feed - Horizontal  method for determination of hepatitis A virus and norovirus in  food using real-time RT-PCR - Part 1: Method for quantification.  Geneva: ISO; 2013. Available from: http://www.iso.org/iso/ catalogue_detail.htm?csnumber=55382 21. International Organization for Standardization (ISO). ISO 9308- 2. Water quality -- Enumeration of Escherichia coli and coliform  bacteria -- Part 2: Most probable number method. Geneva: ISO;  2012. Available from: http://www.iso.org/iso/iso_catalogue/ catalogue_tc/catalogue_detail.htm?csnumber=52246 22. International Organization for Standardization (ISO). ISO 7899- 2. Water quality -- Detection and enumeration of intestinal  enterococci -- Part 2: Membrane filtration method. Geneva:  ISO; 2000. Geneva, Switzerland. Available from: http://www. iso.org/iso/catalogue_detail.htm?csnumber=14854 23. Rnnqvist M, Rtt M, Tuominen P, Salo S, Maunula L.  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Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What are the symptoms?
","{'answer_start': [9786], 'text': ['vomiting, diarrhoea, stomach  pain, and fever.']}"
5,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Novel microbiological and spatial statistical  methods to improve strength of epidemiological evidence  in a community-wide waterborne outbreak. PLoS One.  2014;9(8):e104713. DOI: 10.1371/journal.pone.0104713 PMID:  25147923 18. Kauppinen A, Ikonen J, Pursiainen A, Pitknen T, Miettinen  IT. Decontamination of a drinking water pipeline system  contaminated with adenovirus and Escherichia coli utilizing  peracetic acid and chlorine.J Water Health. 2012;10(3):406-18.  DOI: 10.2166/wh.2012.003 PMID: 22960485 19. Kauppinen A, Martikainen K, Matikka V, Veijalainen A-M,  Pitknen T, Heinonen-Tanski H,  et al.  Sand filters for removal  of microbes and nutrients from wastewater during a one-year  pilot study in a cold temperate climate. J Environ Manage.  2014;133:206-13. DOI: 10.1016/j.jenvman.2013.12.008 PMID:  24384282 8 www.eurosurveillance.org 20. International Organization for Standardization (ISO). ISO/TS  15216-1. 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Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What is the event?
","{'answer_start': [33], 'text': ['outbreaks of gastroenteritis linked to bathing water']}"
29,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. 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DOI: 10.1111/j.1462-2920.2011.02642.x PMID: 22118046 33. Lysn M, Thorhagen M, Brytting M, Hjertqvist M, Andersson  Y, Hedlund KO. Genetic diversity among food-borne and  waterborne norovirus strains causing outbreaks in Sweden.J  Clin Microbiol. 2009;47(8):2411-8. DOI: 10.1128/JCM.02168-08  PMID: 19494060 34. Vega E, Barclay L, Gregoricus N, Shirley SH, Lee D, Vinj J.  Genotypic and epidemiologic trends of norovirus outbreaks  in the United States, 2009 to 2013.J Clin Microbiol.  2014;52(1):147-55. DOI: 10.1128/JCM.02680-13 PMID: 24172151 35. Enriquez CE, Hurst CJ, Gerba CP. Survival of the enteric  adenoviruses 40 and 41 in tap, sea, and waste water.Water  Res. 1995;29(11):2548-53. DOI: 10.1016/0043-1354(95)00070-2 36. Pina S, Puig M, Lucena F, Jofre J, Girones R. Viral pollution in  the environment and in shellfish: human adenovirus detection  by PCR as an index of human viruses.Appl Environ Microbiol.  1998;64(9):3376-82.PMID: 9726885 37. Divizia M, Gabrieli R, Donia D, Macaluso A, Bosch A, Guix S,  et  al.  Waterborne gastroenteritis outbreak in Albania. Water Sci  Technol. 2004;50(1):57-61.PMID: 15318487 38. Kukkula M, Arstila P, Klossner ML, Maunula L, Bonsdorff CH,  Jaatinen P. Waterborne outbreak of viral gastroenteritis.Scand J  Infect Dis. 1997;29(4):415-8. DOI: 10.3109/00365549709011840  PMID: 9360259 39. Rhee EG, Barouch DH. Adenoviruses. In: Mandell G, Bennet  J, Dolin R, editors. Principles and practice of infectious  diseases. 7th ed. Philadelphia: Churchill Livingstone Elsevier.  2010;2027-33. 40. Jovanovi Galovi A, Bijelovi S, Miloevi V, Hrnjakovi  Cvjetkovic I, Popovi M, Kovaevi G,  et al.  Testing for  viral material in water of public bathing areas of the  Danube during summer, Vojvodina, Serbia, 2014. Euro  Surveill. 2016;21(15):30196. DOI: 10.2807/1560-7917. ES.2016.21.15.30196 PMID: 27105473 41. Boehm AB, Ashbolt NJ, Colford JM, Dunbar LE, Fleming LE,  Gold MA,  et al.  A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What are the first steps of mitigation?
","{'answer_start': [7952], 'text': ['Restrictions against bathing ']}"
14,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Novel microbiological and spatial statistical  methods to improve strength of epidemiological evidence  in a community-wide waterborne outbreak. PLoS One.  2014;9(8):e104713. DOI: 10.1371/journal.pone.0104713 PMID:  25147923 18. Kauppinen A, Ikonen J, Pursiainen A, Pitknen T, Miettinen  IT. Decontamination of a drinking water pipeline system  contaminated with adenovirus and Escherichia coli utilizing  peracetic acid and chlorine.J Water Health. 2012;10(3):406-18.  DOI: 10.2166/wh.2012.003 PMID: 22960485 19. Kauppinen A, Martikainen K, Matikka V, Veijalainen A-M,  Pitknen T, Heinonen-Tanski H,  et al.  Sand filters for removal  of microbes and nutrients from wastewater during a one-year  pilot study in a cold temperate climate. J Environ Manage.  2014;133:206-13. DOI: 10.1016/j.jenvman.2013.12.008 PMID:  24384282 8 www.eurosurveillance.org 20. International Organization for Standardization (ISO). ISO/TS  15216-1. Microbiology of food and animal feed - Horizontal  method for determination of hepatitis A virus and norovirus in  food using real-time RT-PCR - Part 1: Method for quantification.  Geneva: ISO; 2013. Available from: http://www.iso.org/iso/ catalogue_detail.htm?csnumber=55382 21. International Organization for Standardization (ISO). ISO 9308- 2. Water quality -- Enumeration of Escherichia coli and coliform  bacteria -- Part 2: Most probable number method. Geneva: ISO;  2012. Available from: http://www.iso.org/iso/iso_catalogue/ catalogue_tc/catalogue_detail.htm?csnumber=52246 22. International Organization for Standardization (ISO). ISO 7899- 2. Water quality -- Detection and enumeration of intestinal  enterococci -- Part 2: Membrane filtration method. Geneva:  ISO; 2000. Geneva, Switzerland. Available from: http://www. iso.org/iso/catalogue_detail.htm?csnumber=14854 23. Rnnqvist M, Rtt M, Tuominen P, Salo S, Maunula L.  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A sea change ahead for recreational water  quality criteria. J Water Health. 2009;7(1):9-20. DOI: 10.2166/ wh.2009.122 PMID: 18957771 42. Fujioka RS, Solo-Gabriele HM, Byappanahalli MN, Kirs M. U.S.  Recreational Water Quality Criteria: A Vision for the Future.Int  J Environ Res Public Health. 2015;12(7):7752-76. DOI: 10.3390/ ijerph120707752 PMID: 26184253 43. Updyke EA, Wang Z, Sun S, Connell C, Kirs M, Wong M,   et al.  Human enteric viruses--potential indicators for  enhanced monitoring of recreational water quality. Virol Sin.  2015;30(5):344-53. DOI: 10.1007/s12250-015-3644-x PMID:  26494480 44. European Union. Commission Implementing Decision 2011/321/ EU of 27 May 2011 establishing, pursuant to Directive 2006/7/ EC of the European Parliament and of the Council, a symbol for  information to the public on bathing water classification and  any bathing prohibition or advice against bathing. Off J. Eur  Union. 2011;L143:38-40. Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
","What measures were taken to prevent the event?
","{'answer_start': [1333], 'text': ['published guidelines for outbreak control']}"
14,Contamination Question Answering,"An increased number of suspected outbreaks of gastroenteritis linked to bathing water were reported to the  Finnish food- and waterborne outbreak (FWO) registry  in July and August 2014. The investigation reports were  assessed by a national outbreak investigation panel.  Eight confirmed outbreaks were identified among the  15 suspected outbreaks linked to bathing water that  had been reported to the FWO registry. According to  the outbreak investigation reports, 1,453 persons  fell ill during these outbreaks. Epidemiological and  microbiological data revealed noroviruses as the main  causative agents. During the outbreaks, exceptionally  warm weather had boosted the use of beaches. Six of  eight outbreaks occurred at small lakes; for those, the  investigation strongly suggested that the beach users  were the source of contamination. In one of those  eight outbreaks, an external source of contamination  was identified and elevated levels of faecal indicator  bacteria (FIB) were noted in water. In the remaining  outbreaks, FIB analyses were insufficient to describe  the hygienic quality of the water. Restrictions against bathing proved effective in controlling the outbreaks.  In spring 2015, the National Institute for Health and  Welfare(THL)and the National Supervisory Authority for Welfare and Health (Valvira) published guidelines for outbreak control to prevent bathing water outbreaks. In July 2014, THL received primary information on several suspected outbreaks linked to bathing water via the media, while no notifications were reported to  the FWO registry. This resulted in direct contacts with  the health authorities, and a reminder about notifying outbreaks related to bathing water was posted in  a THL Infectious Disease Bulletin sent to the municipal  health authorities. The message was also distributed  to municipal environmental authorities by the National  Supervisory Authority for Welfare and Health (Valvira).  Following these reminders, several notifications were  reported to the FWO registry. We identified outbreaks  caused by bathing water from the FWO registry for  2014 and reviewed the epidemiological and microbio- logical data in order to assess and compile guidelines  for outbreak control to prevent similar outbreaks in the  future. Methods Epidemiological investigation We reviewed outbreak notifications and investigation  reports from the FWO registry for 2014. Outbreaks with  a suspected link to bathing water were included in this  study. We evaluated the strength of association for  waterborne outbreaks based on classification criteria  (Table 1) modified from those presented by Tillett et al.  [12] and on information collected from local investigation reports (i.e. time and place of swimming, number  of ill persons, clinical and microbiological findings). Microbiological investigation Description of the laboratories and their roles Analyses of enteric virus were carried out in four  laboratories. Clinical samples were analysed at the  Helsinki University Hospital (HUSLAB) and/or at the  Viral Infection Unit of the National Institute for Health  and Welfare (THL). Water samples were analysed either  at the Water and Health Unit of the National Institute  for Health and Welfare (THL) or at the Department of  Food Hygiene and Environmental Health, University of  Helsinki (UH). Surface samples were analysed at the  UH. Pathogenic bacteria, faecal indicator bacteria (FIB)  and water temperature analyses were conducted in  local clinical and/or environmental laboratories. Clinical samples Viruses were analysed in patients stools for seven out- breaks. At the HUSLAB laboratory, noroviruses were  analysed according to Kanerva et al. [13]. For astrovi- ruses, viral RNA was extracted from a 10% suspension  of the stool using MagNa Pure LC (Roche, Germany).  After RT-PCR, the amplified DNA was detected by liquid  hybridisation using an astrovirus-specific probe [14].  At the THL laboratory, norovirus RNAs were extracted  using the RNeasy Mini Kit (Qiagen, Germany) and the  polymerase/capsid gene junction was amplified as pre- viously described [14]. Genotyping analysis was done  for several norovirus isolates at the THL laboratory.  Viral RNA was amplified in polymerase region A using  a one-step RT-PCR kit (Qiagen) according to Vinj et al.  [15]. Sequences were analysed using Geneious soft- ware. NoroNet online software was used for genotyp- ing. For three outbreaks, stool specimens were tested  for pathogenic bacteria (Campylobacter,Salmonella,  Shigella and Yersinia) by routine methods [16]. Water samples At the THL laboratory, noroviruses and adenoviruses  were concentrated from 0.52 L water samples as  Table1 Classification criteria used for evaluating the strength of  association for waterborne outbreaks, Finland, 2014 A: Same pathogen identified in  patients and in the environment B: Water quality failure or other  deviation in the quality of  environment C: Association between illness  and environment shown in  analytical epidemiological  investigation D: Descriptive epidemiological  investigation suggests that  the outbreak is related to the  environment and excludes  other obvious exposures Strong association: A + C or A + D or B + C. Probable association:  B + D or C or A. Possible association: B or D. Criteria modified from Tillett et al. [12]. 3 www.eurosurveillance.org previously described [17] and using glass fibre pre- filters (Millipore). Viral nucleic acids were extracted  and detected using RT-qPCR and qPCR methods, as  previously described [18,19], with the exception of  using Taqman Environmental Master Mix 2.0 (Life  Technologies) in the adenovirus qPCR. At the UH laboratory, noroviruses and adenoviruses  were concentrated by using membrane disks HA and  Nanoceram to filter a total volume of 4.5 L of water.  When necessary, a prefilter (Waterra) was used, oth- erwise the protocol was as described in Maunula et  al. [14]. As a modification, Taqman primerprobe sets  were applied as published in ISO/TS 152162 [20] for  norovirus GI and GII. Mengovirus was added as a pro- cess control. MPN of E. coli and CFU of intestinal enterococci were  analysed according to standards ISO 93082 and ISO  78992, respectively [21,22]. Surface samples In outbreak IV, 10 environmental swabs were taken  from the toilet facilities (toilets for females, toilets for  males and two latrines). Swabs taken from taps, door  handles and toilet seats were analysed for noroviruses  according to Rnnqvist et al. using nucleic acid detec- tion by RT-qPCR [23]. For adenovirus investigation, a  primerprobe set from Jothikumar et al. was included  [24]. Statistical analyses The statistical analyses were conducted using SPSS 22  software for Windows. The related samples Wilcoxon  signed-rank test was used to test the significance of  temperature and FIB analyses, while comparing the  outbreak samples with frequent-monitoring samples  collected during the summer. Differences were consid- ered significant if the p value was < 0.05. Results Review of the outbreak notifications and  investigation reports In 2014, 15 outbreaks suspected to be caused by bath- ing water were reported to the FWO registry. We identi- fied eight outbreaks in which an association between  bathing water and the illness could be confirmed  based on classification criteria (Table 1). These out- breaks occurred on public beaches in different parts of  Finland in July and August, 2014 (Table 2; Table 3). Six of eight confirmed outbreaks occurred at rather  small lakes or ponds (< 141 ha) and eight of 13 beaches  were categorised as large public beaches with more  than 100 bathers per day (Table 2). According to the  BWD classification criteria based on the last four  bathing seasons, all these large public beaches were  classified as excellent, except for one beach that was  opened in 2012 and therefore did not have data for  classification. Restrictions against bathing were set for each beach  (Table 2). The length of these restrictions varied from  2 days to more than 3 weeks and for one beach, the  advice against bathing was set for the rest of the  bathing season. Seven of eight outbreaks occurred at  inland lakes where no clear source of contamination  was identified according to the bathing water profiles  and/or outbreak investigation reports, although for  five of these outbreaks at inland lakes, non-specific  quality deviations were reported (Table 3). In the one  Table2 Description of beaches with outbreaks linked to recreational water, Finland, summer 2014 (n = 13) Outbreak Type Size (ha) Category Estimated number  of bathers/day EU BWD  classification  (2014)a Estimated outbreak  start time Restriction against  bathing I Lake 2,420 Small < 100 NA 26 July 16 August II Lake 2.9 Large 150500 Excellent 25 July 29 July21 August IIIb Lake 5.5141 2/6 small  4/6 large < 100  > 100 NA  Excellent 2427 July 28 July12 August IV Lake 16.6 Large 1002,000 Excellent 24 July 31 July31 August  (until the end of the  bathing season) V Lake 9.7 Small < 100 NA 3 August 1522 August VI Lake 71.1 Large  150 Excellent 5 August 1121 August VII Sea 393,00,000 Small < 100 NA NK 1315 August and  19 August9  September VIII Lake/pond 0.8 Large 1,000 NAc 27 July 621 August EU BWD: European Unions Bathing Water Directive [5]; NA: not available; NK: not known. a Based on frequent monitoring during the last four bathing seasons [5]. b Combined results from six beaches. c New beach, no classification. 4 www.eurosurveillance.org coastal sea water outbreak, a wastewater overflow was  identified as a potential source of contamination. According to the outbreak investigation reports, 1,453  persons fell ill in these outbreaks (Table 3). The most  common symptoms were vomiting, diarrhoea, stomach  pain, and fever. Information on the incubation period  was available for four outbreaks, the median incuba- tion period ranging from 20 to 62 hours. The dura- tion of illness was reported for five outbreaks, with  a median ranging from 19 to 60 hours. None of the  patients required hospital care. Patient samples were collected in seven outbreaks and  tested for gastrointestinal pathogenic viruses and bacteria. Several types of norovirus were identified, with  norovirus GI.2 detected in three outbreaks (Table 3). In  addition, norovirus GI.4, GII.2 and GII.4 were detected  in patient samples. In one patient, astrovirus was identified. According to outbreak investigation reports,  pathogenic bacteria were analyzed in three investigations (outbreaks III, IV and VIII). Campylobacter was  found in one patient (outbreak III). Salmonella, Shigella  or Yersinia spp. were not found in any of the specimens  tested. Water samples were collected for noro- and adenovi- rus analyses in seven outbreaks, and noro- and/or  adenoviruses were detected in the samples from three  outbreaks (Table 3). In the remaining outbreak, these  analyses were not requested by the municipal health  protection authority. FIB were analysed from water in  all outbreaks. In addition, water quality monitoring was  carried out at every beach according to EU BWD and  national regulations. Elevated levels of both FIB were  found in two of the outbreaks (VII and VIII; Table 4), but  only in outbreak VII did the number of E. coli exceed  the limit for management actions, with maximum con- centrations of 1,100 and 190 CFU/100 mL for E. coli  and enterococci, respectively. Elevated levels of ente- rococci were also noted in outbreak I. In the remain- ing outbreaks, the levels of FIB were low. Overall, no  statistical difference in the levels of E. coli (p = 0.8) or  enterococci (p = 0.086) were noted between the out- break samples (n = 14) and the frequent-monitoring  samples (n = 42), excluding the samples from outbreak  VII, where a clear contamination source was noted. At one outbreak (IV), 10 surface samples from the toi- let area were analysed, and norovirus GII was found on  the tap of the womens toilet. Adenoviruses were not  detected in the surface samples. Water temperature During the outbreak period, exceptionally warm  weather raised the temperature of the bathing water  by several degrees (Table 4). The average tempera- ture of the bathing water samples collected during the  outbreaks was 24.3  1.3 C (n = 16), while the average  temperature of other frequent-monitoring samples col- lected at these beaches in summer 2014 (2 June to 26  August) was 19.4  3.6 C (n = 47; p = 0.002). Table3 Strength of association for waterborne outbreaks, number of patients, virological findings and observed quality deviations,  Finland, summer 2014 (n = 1,453 patients) Outbreak Strength of  associationa No. of  patients Viruses found  in patients No. of virus findings per  water samples tested Viruses found in  water Observed quality  deviation I Possible  (D) 40 NA 0/1 ND Not observed II Probable  (A + B) 85 Norovirus GI.2 2/4 Adenovirus,  norovirus GI Untidy toilets IIIb Strong  (B + C) 819b  1,093c Norovirus GI.2,  GI.4, GII.2 0/3 ND Untidy toilets,  defecation in water IV Strong  (A + B + D) 185 Norovirus GII 0/1 ND Untidy toilets V Probable  (A) 4 Norovirus GI.2  and GII.4 1/2 Norovirus GII Not observed VI Possible  (B) 17 Norovirus (not  typed) 0/2 ND Untidy toilets,  used nappies in  water VII Possible  (B) 2 Norovirus GI NA NA Wastewater  overflow VIII Possible  (B) 27 Astrovirus 1/3 Adenovirus Faeces on the dock NA: not analysed; ND: not detected. a Letters refer to classification criteria detailed in Table 1. b Combined results from six beaches that were investigated in detail. c Total number from all 32 suspected beaches from which the local health authority received notifications of illness. 5 www.eurosurveillance.org Discussion In 2014, an increased number of suspected outbreaks  linked to bathing water were reported to the Finnish  FWO registry. Reminders about the need to notify  outbreaks borne by bathing water were sent to the  municipal authorities and probably triggered the fol- lowing notifications seeing as only one outbreak linked  to bathing water had been reported during the period  2012 to 2013. In addition, the publicity around out- breaks in 2014 probably made the beach users more  alert so that they reported their suspicions of bath- ing water-related sickness to the health authorities.  Generally, it could be difficult to attribute individually  reported gastroenteritis cases to a particular bathing  activity and therefore these outbreaks may remain  undocumented. Nearly 1,500 persons fell ill during the outbreaks linked  to bathing water in 2014. Although the exact number  of people visiting the beaches was not known, some  municipal investigation reports estimated that hun- dreds to thousands of persons per day had been swim- ming at each beach during the outbreak period before  restrictions against bathing were set. In the summer of  2014, the period of continuous hot weather in Finland,  with temperatures of more than 25 C, was exception- ally long and lasted for 38 days [25]. Because of this  heatwave, it is likely that more people than usual were  visiting the beaches and spent more time in the water.  A previous study noted a positive correlation between  the number of days with temperatures over 25 C and  the number of outbreaks per bathing season [26]. Some  investigation reports also stated that the toilets at the  beaches were untidy, rubbish bins were overloaded,  and used nappies were floating in the water, indicating  overcrowded conditions. In 2015, no outbreaks linked  to bathing water were reported. This was probably due  in part to the weather conditions, namely 3 days with  temperatures over 25 C in July 2015, compared with 26  such days in July 2014. In Helsinki, the average tem- perature and precipitation in July differed considerably  between 2015 and 2014 (16.2 C/76.1 mm vs 20 C/12.5  mm) [27]. Most of the beaches were small, suggesting that the  volume of users exceeded the self-cleaning capacity  of the beach. For example, the volume of the smallest  lake (outbreak VIII) is 20,800 m3. In theory, if a single  infected person excreted large numbers of noroviruses  (up to 1011 genomic copies/g) [28], and if these viruses  were evenly diluted in the total volume of the lake, 1 g  of faeces would result in a virus concentration of nearly  5,000 genomic copies/L. Considering the low infectious  dose of norovirus (as few as 18 virus particles) [29] and  the average ingestion of water while swimming (37 mL  and 16 mL for children and adults, respectively, per  Table4 Levels of faecal indicator bacteria and water temperature in outbreak samples (n = 17) and frequent-monitoring samples  (n = 47), Finland, summer 2014 Outbreak No. of analysed water samples Escherichia coli   MPN/100 mL Intestinal enterococci  CFU/100 mL Temperature  C I  Outbreak samples  Monitoring samples   1  3   6  8  6   190  4  2   25.7  22.1  3.3 II  Outbreak samples  Monitoring samples   2  6   39  26  72  72   9  8  6  4   25.0  1.4  20.5  4.4 IIIa  Outbreak samples  Monitoring samples   5  18   14  10  19  4   3  3  15  22   25.2  0  19.0  3.8 IV  Outbreak samples  Monitoring samples   1  4   9  3  3   7  1  2   24.0  19.8  4.2 V  Outbreak samples  Monitoring samples   1  2   12  34  47   22  6  8   24.0  19.3  2.5 VI  Outbreak samples  Monitoring samples   2  4   4  1  1  0   3  2  1  1   23.0  0  17.5  3.7 VII  Outbreak samples  Monitoring samples   3  5   670  580  2  4   110  98  4  4   22.3  1b  20.2  3.5 VIII  Outbreak samples  Monitoring samples   2  5   130  120  17  5   48  46  8  7   23.9  1  18.1  2.2 CFU: colony-forming units; MPN: most probable number. a Combined results from the five beaches for which indicator bacteria were analysed. b Average from n = 2 samples. 6 www.eurosurveillance.org 45 min swimming session [30]), it is obvious that the  bathing water at this particular beach would have the  potential to cause a considerable number of infections. Norovirus was detected in ill persons in most of the out- breaks. The symptoms reported by municipal authori- ties fit the clinical picture of a norovirus illness [31]. In  three outbreaks, norovirus GI.2 was identified. In addi- tion, also GI.4, GII.2 and GII.4 were detected in patient  samples. The prevalence of GI in these outbreaks is  consistent with the observation that GI genotypes are  more frequently involved in food- or waterborne out- breaks than GII, which could imply that GI is more sta- ble in the environment [32,33]. Genotype GII.4 is the  most common genotype causing infections in humans  and is more likely to be associated with person-to-per- son transmission [34]. In two outbreaks, norovirus GI and GII were found in  bathing water and in one outbreak, GII was determined  in a swab taken from the tap of the toilet, but the num- ber of particles obtained was too small to allow typ- ing of these viruses. Therefore, an exact comparison  between patient and water samples could not be car- ried out. In two outbreaks, adenovirus was found in  water. Adenoviruses are commonly found in human  wastewater and owing to their high stability in aqueous  environments, they are recognised as good viral indi- cators of human sewage pollution [19,35,36]. Moreover,  adenoviruses can spread via contaminated water  and they have been linked to waterborne outbreaks  [14,37,38]. Since adenoviruses most often result in  subclinical disease, and symptomatic infections tend  to be mild and self-resolving, most infections remain  undocumented [39]. In the outbreaks of this study, no  adenoviruses were identified in ill persons. In Finland, the hygienic quality of the bathing water is  evaluated according to BWD and national regulations  [3-5]. According to Finnish legislation, the minimum  number of bathing water samples to be taken during  a bathing season is three for small public beaches  and four for large public beaches. The legislation con- tains rules how to monitor and manage bathing waters,  indicates microbiological threshold values, regulates  measures to be taken when bathing water fails to meet  the quality and requires the dissemination of informa- tion about bathing water quality. In Finland, the concen- trations of FIB in bathing water are typically very low;  70% of the E. coli and 58% of the intestinal enterococci  concentrations were < 10 CFU or MPN/100 mL in bathing  water samples collected from all large public beaches  (n = 302) during the seasons from 2013 to 2015 (data  not shown). In this study, the microbiological thresh- old for management actions was exceeded only in one  of eight outbreaks. For this outbreak, a clear external  contamination source was identified as 2,0003,000  m3 of raw wastewater had overflowed near the bath- ing site. In the other outbreaks, the levels of FIB were  low and the bathing water quality was classified as  excellent according to the BWD criteria. The sources of  contamination in these outbreaks were most probably  the bathers and other beach users. This suggestion  is supported by the observed pollution of the beach  environment. The poor indicator value of FIB in these outbreaks raises  questions about the current practices for assessing  bathing water quality. This finding is consistent with  a recent study showing high prevalence of adenovi- ruses (75%) in bathing water samples, which neverthe- less complied with the regulations for recreational use  [40]. Moreover, Boehm et al. reviewed the lack of cor- relation between FIB and human pathogen concentra- tions and between FIB and human health, especially in  recreational areas of non-point-source contamination  [41]. It is also widely known that pathogenic microbes,  especially enteric viruses, survive substantially bet- ter than the currently used FIB in water environments.  Therefore, new candidates, such as Clostridium per- fringens, coliphages, Bacteroides and human enteric  viruses as well as new genomic approaches, e.g.  metagenomics, have been proposed for water quality  assessment [41-43]. However, during the summer, the  higher temperature of bathing water and the increased  amount of ultraviolet light have a negative impact on  microbe survival. In this study, noro- and adenoviruses  in outbreak II were detected in the water on at least  six days but fewer than 12 days. These relatively short  contamination episodes may remain undetected with  routine FIB sampling. In most of the outbreaks, the  quality of bathing water was questioned only after people visiting the beaches fell ill, and restrictions against  bathing were set for the beaches only then. The length  of the restrictions was determined according to the  results of water analyses and proved effective in con- trolling of the outbreaks. Investigation reports of outbreaks linked to bathing  water were assessed by a panel that included experts  from THL, Valvira and UH. By using agreed criteria,  reports can be assessed more consistently over time  [12]. When the same pathogen has been identified in  patients and in the beach environment, results from  the analytical epidemiological study point towards a  certain source and water quality failures have been  detected, outbreaks are often easy to categorise. More  discussion in the panel will be needed on the relation  between illness and the beach environment when pol- lution of the beach is mentioned but no obvious other  exposures are described in outbreak reports. In this  study, eight outbreaks were identified among the 15  outbreaks suspected to be caused by bathing water  that were reported to the FWO registry. Four outbreaks  were classified as having a strong or probable associa- tion with the beach environment, and four as having a  possible association. Analytical epidemiological inves- tigations were lacking in all but one investigation, indi- cating that more training and practical experience in  analytical epidemiology may be needed in the munici- pal outbreak investigation groups. 7 www.eurosurveillance.org Because of an increase in the number of bathing water  outbreaks in the summer of 2014, THL and Valvira pub- lished guidelines for outbreak control in spring 2015 to  prevent bathing water outbreaks. If, based on the labo- ratory or epidemiological findings, the water is consid- ered to be contaminated, visitors should be informed  about a bathing prohibition or advice against bath- ing should be posted by means of the international  symbols presented in the Commission Implementing  Decision (2011/321/EU) [44]. To prevent outbreaks,  rooms intended for washing and dressing as well as  toilets at the beach should be kept clean, and soap,  hand towels and toilet paper should be available.  Visitors should be encouraged to wash their hands or  use freshen-up towels. Nappies should not be changed  and the babies bottoms should not be washed in the  bathing water, and people with gastrointestinal illness  should avoid swimming. In the case of an outbreak  suspicion, municipal authorities should notify the FWO  registry and an outbreak investigation, including epi- demiological and microbiological analyses, should be  initiated. Acknowledgements Appreciation is given to the municipal health authorities for  their investigations and assistance. We acknowledge the  help of the personnel at the National Institute for Health  and Welfare and the University of Helsinki. The research at  THL was partly supported by the personal research grant to  Ari Kauppinen from the Doctoral School of the University of  Eastern Finland. The research at UH was partly supported by  EU project Aquavalens (311846). Conflict of interest None declared. Authors contributions Ari Kauppinen, Haider Al-Hello, Outi Zacheus, Jaana  Kilponen, Leena Maunula, Sari Huusko, Ilkka Miettinen,  Soile Blomqvist and Ruska Rimhanen-Finne participated in  the national outbreak evaluation panel and the design of  the study. Ruska Rimhanen-Finne coordinated the national  panel. Ari Kauppinen was responsible for performing the  data analyses and virus analyses from water performed at  THL. Haider Al-Hello, Soile Blomqvist and Maija Lappalainen  were responsible for analysing viruses from patient samples.  Leena Maunula was responsible for analysing viruses from  the water and environmental samples performed at UH. Ari  Kauppinen and Ruska Rimhanen-Finne drafted the manu- script. All authors were involved in the preparation and re- view of the manuscript and approved the final version. References 1. Zacheus O, Miettinen IT. Increased information on waterborne  outbreaks through efficient notification system enforces  actions towards safe drinking water.J Water Health.  2011;9(4):763-72. DOI: 10.2166/wh.2011.021 PMID: 22048435 2. Finnish Decree. Valtioneuvoston asetus elintarvikkeiden ja  veden vlityksell levivien epidemioiden selvittmisest.  [Government Decree concerning the follow-up and reporting  of food- and waterborne outbreaks]. Document no. 1365/2011.  Helsinki: Finlex database; 2011. Finnish. Available from: http:// www.finlex.fi/fi/laki/alkup/2011/20111365 3. 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Available from: http://eur-lex.europa. eu/eli/dec_impl/2011/321/oj License and copyright This is an open-access article distributed under the terms of  the Creative Commons Attribution (CC BY 4.0) Licence. You  may share and adapt the material, but must give appropriate  credit to the source, provide a link to the licence, and indi- cate if changes were made. This article is copyright of the authors, 2017. 
",What is the source of contamination?,"{'answer_start': [799], 'text': ['beach users']}"
18,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  This work was supported by grants from the Research and  Development Unit, Jmtland County Council, Sweden, and the  Medical Faculty of Ume University, Ume, Sweden. Dr Widerstrm is the county medical officer at the Depart- ment of Communicable Diseases Control and Prevention, Coun- ty Council of Jmtland, Sweden, and senior infectious disease  consultant at the Department of Infectious Diseases, stersund  Hospital. His primary research interests include epidemiology of  communicable diseases, especially healthcare-associated staphy- lococcal infections. References   1. Chalmers RM, Katzer F. Looking for Cryptosporidium: the   application of advances in detection and diagnosis. Trends Parasitol.  2013;29:23751. http://dx.doi.org/10.1016/j.pt.2013.03.001   2. Bouzid M, Hunter PR, Chalmers RM, Tyler KM. Cryptosporidium  pathogenicity and virulence. Clin Microbiol Rev. 2013;26:11534.  http://dx.doi.org/10.1128/CMR.00076-12   3. 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Exp Parasitol. 2010;124:319. http://dx.doi. org/10.1016/j.exppara.2009.09.020 28. Manthey MW, Ross AB, Soergel KH. Cryptosporidiosis and  inflammatory bowel disease. Experience from the Milwau- kee outbreak. Dig Dis Sci. 1997;42:15806. http://dx.doi. org/10.1023/A:1018828507990 29. Savioli L, Smith H, Thompson A. Giardia and Cryptosporidium join  the Neglected Diseases Initiative. Trends Parasitol. 2006;22:203 8. http://dx.doi.org/10.1016/j.pt.2006.02.015 30. Chalmers RM, Hadfield SJ, Jackson CJ, Elwin K, Xiao L, Hunter P.   Geographic linkage and variation in Cryptosporidium hominis.  Emerg Infect Dis. 2008;14:4968. http://dx.doi.org/10.3201/ eid1403.071320 31. Li N, Xiao L, Cama V, Ortega Y, Gilman R, Guo M, et al.   Genetic recombination and Cryptosporidium hominis virulent sub- type IbA10G2. Emerg Infect Dis. 2013;19:157382. http://dx.doi. org/10.3201/eid1910.121361 32. Waldron LS, Dimeski B, Beggs PJ, Ferrari BC, Power ML.   Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What is the initial cause of the event?
","{'answer_start': [25017], 'text': ['contamination of surface water by human sewage']}"
22,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What is the date of the event?
","{'answer_start': [3], 'text': ['November 2010']}"
18,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  This work was supported by grants from the Research and  Development Unit, Jmtland County Council, Sweden, and the  Medical Faculty of Ume University, Ume, Sweden. Dr Widerstrm is the county medical officer at the Depart- ment of Communicable Diseases Control and Prevention, Coun- ty Council of Jmtland, Sweden, and senior infectious disease  consultant at the Department of Infectious Diseases, stersund  Hospital. His primary research interests include epidemiology of  communicable diseases, especially healthcare-associated staphy- lococcal infections. References   1. Chalmers RM, Katzer F. Looking for Cryptosporidium: the   application of advances in detection and diagnosis. Trends Parasitol.  2013;29:23751. http://dx.doi.org/10.1016/j.pt.2013.03.001   2. Bouzid M, Hunter PR, Chalmers RM, Tyler KM. Cryptosporidium  pathogenicity and virulence. Clin Microbiol Rev. 2013;26:11534.  http://dx.doi.org/10.1128/CMR.00076-12   3. 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Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What is the location of the event?
","{'answer_start': [57], 'text': ['Sweden']}"
13,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","How was the event first detected?
","{'answer_start': [6221], 'text': ['received reports from several employers that  10%-20% of employees had gastroenteritis.']}"
22,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","How many people were ill?
","{'answer_start': [18], 'text': ['27,000']}"
30,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Karanis P, Kourenti C, Smith H. Waterborne transmission of proto- zoan parasites: a worldwide review of outbreaks and lessons learnt.   J Water Health. 2007;5:138. http://dx.doi.org/10.2166/wh.2006.002 13. Hayes EB, Matte TD, OBrien TR, McKinley TW, Logs- don GS, Rose JB, et al. Large community outbreak of cryp- tosporidiosis due to contamination of a filtered public water   supply. N Engl J Med. 1989;320:13726. http://dx.doi.org/10.1056/ NEJM198905253202103 14. Mac Kenzie WR, Hoxie NJ, Proctor ME, Gradus MS, Blair KA,   Peterson DE, et al. A massive outbreak in Milwaukee of cryptosporidi- um infection transmitted through the public water supply. N Engl J Med.  1994;331:1617. http://dx.doi.org/10.1056/NEJM199407213310304 15. McLauchlin J, Amar C, Pedraza-Diaz S, Nichols GL. Molecular  epidemiological analysis of Cryptosporidium spp. in the United  Kingdom: results of genotyping Cryptosporidium spp. in 1,705 fecal  samples from humans and 105 fecal samples from livestock animals.  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Syndromic surveillance for local outbreak detec- tion and awareness: evaluating outbreak signals of acute gastroen- teritis in telephone triage, Web-based queries and over-the-counter  pharmacy sales. Epidemiol Infect. 2014;142:30313. http://dx.doi. org/10.1017/S0950268813001088 20. Casemore DP. ACP Broadsheet 128: June 1991. Laboratory methods  for diagnosing cryptosporidiosis. J Clin Pathol. 1991;44:44551.  http://dx.doi.org/10.1136/jcp.44.6.445 21. Xiao L, Bern C, Limor J, Sulaiman I, Roberts J, Checkley W,   et al. Identification of 5 types of Cryptosporidium parasites in chil- dren in Lima, Peru. J Infect Dis. 2001;183:4927. http://dx.doi. org/10.1086/318090 22. Alves M, Xiao L, Sulaiman I, Lal AA, Matos O, Antunes F. Sub- genotype analysis of Cryptosporidium isolates from humans, cattle,  and zoo ruminants in Portugal. J Clin Microbiol. 2003;41:27447.  http://dx.doi.org/10.1128/JCM.41.6.2744-2747.2003 23. Loveridge P, Cooper D, Elliot AJ, Harris J, Gray J, Large S, et al.  Vomiting calls to NHS Direct provide an early warning of norovirus  outbreaks in hospitals. J Hosp Infect. 2010;74:38593. http://dx.doi. org/10.1016/j.jhin.2009.10.007 24. Keller M, Blench M, Tolentino H, Freifeld CC, Mandl KD,  Mawudeku A, et al. Use of unstructured event-based reports  for global infectious disease surveillance. Emerg Infect Dis.  2009;15:68995. http://dx.doi.org/10.3201/eid1505.081114 25. Public Health Laboratory Study Group. Cryptosporidiosis in England  and Wales: prevalence and clinical and epidemiological features.  BMJ. 1990;300:7747. http://dx.doi.org/10.1136/bmj.300.6727.774 26. Mason BW, Chalmers RM, Carnicer-Pont D, Casemore DP.   A Cryptosporidium hominis outbreak in north-west Wales associated  with low oocyst counts in treated drinking water. J Water Health.  2010;8:299310. http://dx.doi.org/10.2166/wh.2009.184 27. Yoder JS, Beach MJ. Cryptosporidium surveillance and risk factors  in the United States. Exp Parasitol. 2010;124:319. http://dx.doi. org/10.1016/j.exppara.2009.09.020 28. Manthey MW, Ross AB, Soergel KH. Cryptosporidiosis and  inflammatory bowel disease. Experience from the Milwau- kee outbreak. Dig Dis Sci. 1997;42:15806. http://dx.doi. org/10.1023/A:1018828507990 29. Savioli L, Smith H, Thompson A. Giardia and Cryptosporidium join  the Neglected Diseases Initiative. Trends Parasitol. 2006;22:203 8. http://dx.doi.org/10.1016/j.pt.2006.02.015 30. Chalmers RM, Hadfield SJ, Jackson CJ, Elwin K, Xiao L, Hunter P.   Geographic linkage and variation in Cryptosporidium hominis.  Emerg Infect Dis. 2008;14:4968. http://dx.doi.org/10.3201/ eid1403.071320 31. Li N, Xiao L, Cama V, Ortega Y, Gilman R, Guo M, et al.   Genetic recombination and Cryptosporidium hominis virulent sub- type IbA10G2. Emerg Infect Dis. 2013;19:157382. http://dx.doi. org/10.3201/eid1910.121361 32. Waldron LS, Dimeski B, Beggs PJ, Ferrari BC, Power ML.   Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What is the attack rate?
","{'answer_start': [8170], 'text': ['50%']}"
33,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What are the pathogens?
","{'answer_start': [16630], 'text': ['Cryptosporidium oocysts']}"
12,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  This work was supported by grants from the Research and  Development Unit, Jmtland County Council, Sweden, and the  Medical Faculty of Ume University, Ume, Sweden. Dr Widerstrm is the county medical officer at the Depart- ment of Communicable Diseases Control and Prevention, Coun- ty Council of Jmtland, Sweden, and senior infectious disease  consultant at the Department of Infectious Diseases, stersund  Hospital. His primary research interests include epidemiology of  communicable diseases, especially healthcare-associated staphy- lococcal infections. References   1. Chalmers RM, Katzer F. Looking for Cryptosporidium: the   application of advances in detection and diagnosis. Trends Parasitol.  2013;29:23751. http://dx.doi.org/10.1016/j.pt.2013.03.001   2. Bouzid M, Hunter PR, Chalmers RM, Tyler KM. Cryptosporidium  pathogenicity and virulence. Clin Microbiol Rev. 2013;26:11534.  http://dx.doi.org/10.1128/CMR.00076-12   3. 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Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What are the symptoms?
","{'answer_start': [507], 'text': ['diarrhea']}"
23,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What is the event?
","{'answer_start': [95], 'text': ['outbreak of cryptosporidiosis']}"
28,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  This work was supported by grants from the Research and  Development Unit, Jmtland County Council, Sweden, and the  Medical Faculty of Ume University, Ume, Sweden. Dr Widerstrm is the county medical officer at the Depart- ment of Communicable Diseases Control and Prevention, Coun- ty Council of Jmtland, Sweden, and senior infectious disease  consultant at the Department of Infectious Diseases, stersund  Hospital. His primary research interests include epidemiology of  communicable diseases, especially healthcare-associated staphy- lococcal infections. References   1. Chalmers RM, Katzer F. Looking for Cryptosporidium: the   application of advances in detection and diagnosis. Trends Parasitol.  2013;29:23751. http://dx.doi.org/10.1016/j.pt.2013.03.001   2. Bouzid M, Hunter PR, Chalmers RM, Tyler KM. Cryptosporidium  pathogenicity and virulence. Clin Microbiol Rev. 2013;26:11534.  http://dx.doi.org/10.1128/CMR.00076-12   3. 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Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What are the initial steps of investigation?
","{'answer_start': [7149], 'text': ['questionnaire']}"
7,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Karanis P, Kourenti C, Smith H. Waterborne transmission of proto- zoan parasites: a worldwide review of outbreaks and lessons learnt.   J Water Health. 2007;5:138. http://dx.doi.org/10.2166/wh.2006.002 13. Hayes EB, Matte TD, OBrien TR, McKinley TW, Logs- don GS, Rose JB, et al. Large community outbreak of cryp- tosporidiosis due to contamination of a filtered public water   supply. N Engl J Med. 1989;320:13726. http://dx.doi.org/10.1056/ NEJM198905253202103 14. Mac Kenzie WR, Hoxie NJ, Proctor ME, Gradus MS, Blair KA,   Peterson DE, et al. A massive outbreak in Milwaukee of cryptosporidi- um infection transmitted through the public water supply. N Engl J Med.  1994;331:1617. http://dx.doi.org/10.1056/NEJM199407213310304 15. McLauchlin J, Amar C, Pedraza-Diaz S, Nichols GL. Molecular  epidemiological analysis of Cryptosporidium spp. in the United  Kingdom: results of genotyping Cryptosporidium spp. in 1,705 fecal  samples from humans and 105 fecal samples from livestock animals.  J Clin Microbiol. 2000;38:398490. 16. Fournet N, Deege MP, Urbanus AT, Nichols G, Rosner BM,   Chalmers RM, et al. Simultaneous increase of Cryptosporidium in- fections in the Netherlands, the United Kingdom and Germany in  late summer season, 2012. Euro Surveill. 2013;18: pii: 203488490. 17. Insulander M, Lebbad M, Stenstrom TA, Svenungsson B. An out- break of cryptosporidiosis associated with exposure to swimming  pool water. Scand J Infect Dis. 2005;37:35460. http://dx.doi. org/10.1080/00365540410021072 18. Swedish Institute for Communicable Disease Control. Giar- dia and Cryptosporidium in surface water from Swedish wa- ter works [in Swedish, English summary]. [cited Feb 7]. http:// folkhalsomyndigheten.se/publicerat-material/publikationer/  Giardia-och-Cryptosporidium-i-svenska-ytvattentakter/ 19. Andersson T, Bjelkmar P, Hulth A, Lindh J, Stenmark S,   Widerstr  om M. Syndromic surveillance for local outbreak detec- tion and awareness: evaluating outbreak signals of acute gastroen- teritis in telephone triage, Web-based queries and over-the-counter  pharmacy sales. Epidemiol Infect. 2014;142:30313. http://dx.doi. org/10.1017/S0950268813001088 20. Casemore DP. ACP Broadsheet 128: June 1991. Laboratory methods  for diagnosing cryptosporidiosis. J Clin Pathol. 1991;44:44551.  http://dx.doi.org/10.1136/jcp.44.6.445 21. Xiao L, Bern C, Limor J, Sulaiman I, Roberts J, Checkley W,   et al. Identification of 5 types of Cryptosporidium parasites in chil- dren in Lima, Peru. J Infect Dis. 2001;183:4927. http://dx.doi. org/10.1086/318090 22. Alves M, Xiao L, Sulaiman I, Lal AA, Matos O, Antunes F. Sub- genotype analysis of Cryptosporidium isolates from humans, cattle,  and zoo ruminants in Portugal. J Clin Microbiol. 2003;41:27447.  http://dx.doi.org/10.1128/JCM.41.6.2744-2747.2003 23. Loveridge P, Cooper D, Elliot AJ, Harris J, Gray J, Large S, et al.  Vomiting calls to NHS Direct provide an early warning of norovirus  outbreaks in hospitals. J Hosp Infect. 2010;74:38593. http://dx.doi. org/10.1016/j.jhin.2009.10.007 24. Keller M, Blench M, Tolentino H, Freifeld CC, Mandl KD,  Mawudeku A, et al. Use of unstructured event-based reports  for global infectious disease surveillance. Emerg Infect Dis.  2009;15:68995. http://dx.doi.org/10.3201/eid1505.081114 25. Public Health Laboratory Study Group. Cryptosporidiosis in England  and Wales: prevalence and clinical and epidemiological features.  BMJ. 1990;300:7747. http://dx.doi.org/10.1136/bmj.300.6727.774 26. Mason BW, Chalmers RM, Carnicer-Pont D, Casemore DP.   A Cryptosporidium hominis outbreak in north-west Wales associated  with low oocyst counts in treated drinking water. J Water Health.  2010;8:299310. http://dx.doi.org/10.2166/wh.2009.184 27. Yoder JS, Beach MJ. Cryptosporidium surveillance and risk factors  in the United States. Exp Parasitol. 2010;124:319. http://dx.doi. org/10.1016/j.exppara.2009.09.020 28. Manthey MW, Ross AB, Soergel KH. Cryptosporidiosis and  inflammatory bowel disease. Experience from the Milwau- kee outbreak. Dig Dis Sci. 1997;42:15806. http://dx.doi. org/10.1023/A:1018828507990 29. Savioli L, Smith H, Thompson A. Giardia and Cryptosporidium join  the Neglected Diseases Initiative. Trends Parasitol. 2006;22:203 8. http://dx.doi.org/10.1016/j.pt.2006.02.015 30. Chalmers RM, Hadfield SJ, Jackson CJ, Elwin K, Xiao L, Hunter P.   Geographic linkage and variation in Cryptosporidium hominis.  Emerg Infect Dis. 2008;14:4968. http://dx.doi.org/10.3201/ eid1403.071320 31. Li N, Xiao L, Cama V, Ortega Y, Gilman R, Guo M, et al.   Genetic recombination and Cryptosporidium hominis virulent sub- type IbA10G2. Emerg Infect Dis. 2013;19:157382. http://dx.doi. org/10.3201/eid1910.121361 32. Waldron LS, Dimeski B, Beggs PJ, Ferrari BC, Power ML.   Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What are the first steps of mitigation?
","{'answer_start': [6771], 'text': ['boil-water advisory']}"
20,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What measures were taken to prevent the event?
","{'answer_start': [930], 'text': ['optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens']}"
5,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  This work was supported by grants from the Research and  Development Unit, Jmtland County Council, Sweden, and the  Medical Faculty of Ume University, Ume, Sweden. Dr Widerstrm is the county medical officer at the Depart- ment of Communicable Diseases Control and Prevention, Coun- ty Council of Jmtland, Sweden, and senior infectious disease  consultant at the Department of Infectious Diseases, stersund  Hospital. His primary research interests include epidemiology of  communicable diseases, especially healthcare-associated staphy- lococcal infections. References   1. Chalmers RM, Katzer F. Looking for Cryptosporidium: the   application of advances in detection and diagnosis. Trends Parasitol.  2013;29:23751. http://dx.doi.org/10.1016/j.pt.2013.03.001   2. Bouzid M, Hunter PR, Chalmers RM, Tyler KM. Cryptosporidium  pathogenicity and virulence. Clin Microbiol Rev. 2013;26:11534.  http://dx.doi.org/10.1128/CMR.00076-12   3. 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Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
","What was the age of the affected people?
","{'answer_start': [12942], 'text': ['44 years ']}"
16,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Molecular epidemiology, spatiotemporal analysis, and ecology  of sporadic human cryptosporidiosis in Australia. Appl Environ   Microbiol.  2011;77:775765.  http://dx.doi.org/10.1128/AEM.  00615-11 33. Zhou L, Singh A, Jiang J, Xiao L. Molecular surveillance of   Cryptosporidium spp. in raw wastewater in Milwaukee: implications  for understanding outbreak occurrence and transmission dynam- ics. J Clin Microbiol. 2003;41:52547. http://dx.doi.org/10.1128/ JCM.41.11.5254-5257.2003 34. Chalmers RM, Robinson G, Elwin K, Hadfield SJ, Thomas E,   Watkins J, et al. Detection of Cryptosporidium species and sources  of contamination with Cryptosporidium hominis during a water- borne outbreak in north west Wales. J Water Health. 2010;8:31125.  http://dx.doi.org/10.2166/wh.2009.185 35. McDonald AC, Mac Kenzie WR, Addiss DG, Gradus MS,   Linke G, Zembrowski E, et al. Cryptosporidium parvumspecific  antibody responses among children residing in Milwaukee dur- ing the 1993 waterborne outbreak. J Infect Dis. 2001;183:13739.   http://dx.doi.org/10.1086/319862 36. Borad A, Ward H. Human immune responses in cryptosporidiosis. Fu- ture Microbiol. 2010;5:50719. http://dx.doi.org/10.2217/fmb.09.128 37. Howe AD, Forster S, Morton S, Marshall R, Osborn KS, Wright P,  et al. Cryptosporidium oocysts in a water supply associated with  a cryptosporidiosis outbreak. Emerg Infect Dis. 2002;8:61924.  http://dx.doi.org/10.3201/eid0806.010271 38. Ongerth JE. The concentration of Cryptosporidium and Giardia  in waterthe role and importance of recovery efficiency.   Water Res. 2013;47:247988. http://dx.doi.org/10.1016/j.watres.  2013.02.015 39. Causer LM, Handzel T, Welch P, Carr M, Culp D, Lucht R, et al.  An outbreak of Cryptosporidium hominis infection at an Illinois  recreational waterpark. Epidemiol Infect. 2006;134:14756. http:// dx.doi.org/10.1017/S0950268805004619 40. Gallas-Lindemann C, Sotiriadou I, Plutzer J, Karanis P. Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
",What is the source of contamination?,"{'answer_start': [24923], 'text': ['Water Supply']}"
30,Contamination Question Answering,"In November 2010, 27,000 (45%) inhabitants of  stersund, Sweden, were affected by a waterborne outbreak of cryptosporidiosis. The outbreak was characterized  by a rapid onset and high attack rate, especially among  young and middle-aged persons. Young age, number of infected family members, amount of water consumed daily,  and gluten intolerance were identified as risk factors for  acquiring cryptosporidiosis. Also, chronic intestinal disease  and young age were significantly associated with prolonged diarrhea. Identification of Cryptosporidium hominis subtype  IbA10G2 in human and environmental samples and consistently low numbers of oocysts in drinking water confirmed insufficient reduction of parasites by the municipal water treatment plant. The current outbreak shows that use of inadequate microbial barriers at water treatment plants can  have serious consequences for public health. This risk can be minimized by optimizing control of raw water quality and employing multiple barriers that remove or inactivate all groups of pathogens. Protozoan parasites of the genus Cryptosporidium can cause gastrointestinal illness in humans and animals  (1). Twenty-six species and >60 genotypes have been identified (2). C. parvum and C. hominis are the most prevalent species that infect humans (1,3). Cryptosporidiosis is  transmitted mainly by the fecal-oral route, usually through   oocyst-contaminated water or food or by direct contact  with an infected person or animal (2). Infectivity is dose de- pendent and certain subtypes are apparently more virulent,   requiring only a few oocysts to establish infection (1,4). In  healthy persons, gastrointestinal symptoms usually resolve  spontaneously within 12 weeks, although asymptomatic  carriage can occur (2). Nonetheless, in immunocompromised patients, severe life-threatening watery diarrhea can develop (2). Information is limited regarding the long-term  effects of Cryptosporidium infection (3,5,6). The global incidence of cryptosporidiosis is largely  unknown, although the disease was recently identified as  one of the major causes of moderate to severe diarrhea in  children <5 years of age in low-income countries (7). In  Sweden, cryptosporidiosis has been a notifiable disease  since 2004, and 150 cases (1.7/100,000 population/year)  were reported annually until 2009. However, cryptosporid- iosis is probably underreported, mainly because sampling  from patients with gastrointestinal symptoms and requests  for diagnostic tests are insufficient (3,8). Because of some inherent characteristics of the patho- gen, Cryptosporidium infection has critical public health  implications for drinking water and recreational waters.  The oocysts are excreted in large numbers in feces, can  survive for months in the environment (5), and are resis- tant to the concentrations of chlorine commonly used to  treat drinking water (9). The first reported outbreak of wa- terborne human cryptosporidiosis occurred in the United  States in 1984 (10), and since then, numerous outbreaks  involving up to hundreds of persons have been identified  in several parts of the world (11,12). However, only a  few very large outbreaks have been documented (1315);  the most extensive occurred in 1993 in Milwaukee, Wis- consin, USA, in which 400,000 persons were infected  with Cryptosporidium oocysts by drinking water from a  Large Outbreak of   Cryptosporidium hominis Infection  Transmitted through the   Public Water Supply, Sweden Micael Widerstrm, Caroline Schnning, Mikael Lilja, Marianne Lebbad, Thomas Ljung,   Grel Allestam, Martin Ferm, Britta Bjrkholm, Anette Hansen, Jari Hiltula, Jonas Lngmark,  Margareta Lfdahl, Maria Omberg, Christina Reuterwall, Eva Samuelsson, Katarina Widgren,   Anders Wallensten, and Johan Lindh   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  581 Author affiliations: Ume University, Ume, Sweden (M. Widerstrm,   M. Lilja, M. Ferm, C. Reuterwall, E. Samuelsson); Jmtland County  Council, stersund, Sweden (M. Widerstrm, M. Omberg); Public  Health Agency of Sweden, Solna, Sweden (C. Schnning, M. Leb- bad, G. Allestam, B. Bjrkholm, A. Hansen, J. Lngmark, M. Lf- dahl, K. Widgren, A. Wallensten, J. Lindh); Mid Sweden University,  stersund (T. Ljung); stersund Municipality, stersund (J. Hitula);  and Karolinska Institutet, Stockholm (J. Lindh) DOI: http://dx.doi.org/10.3201/eid2004.121415 RESEARCH water treatment plant (WTP) (14). Cryptosporidium spp.  are the predominant protozoan parasites causing water- borne outbreaks worldwide (11). In 2012, an increase in  Cryptosporidium infections, particularly by C. hominis  IbA10G2, was reported in Europe (16). In Sweden, only 1 drinking water outbreak involving  Cryptosporidium has been recognized (Y. Andersson, pers.  comm.), and a C. parvum outbreak associated with fecal  contamination of a public swimming pool occurred in 2002  and affected 1,000 persons (17). A study of Cryptospo- ridium species and subtypes isolated from samples from  194 patients in Sweden during 20062008 identified 111 C.  parvum infections and 65 C. hominis infections. Most pa- tients with C. hominis infection had been infected abroad,  and only 3 were considered to have sporadic domestic in- fections (3). A recent investigation of Cryptosporidium in  raw water from 7 large WTPs in Sweden (not including the  WTP of interest in the present study) identified 23 (11.5%)  of 200 positive samples containing 130 oocysts/10 L, al- though neither species nor subtypes were analyzed (18). The city of stersund is located in central Sweden and  has a population of 60,000. The major WTP in stersund  (WTP-) draws surface water from nearby Lake Storsjn  and supplies drinking water to 51,000 of the citys inhab- itants. At the time of the onset of the outbreak reported  here, the purification process at WTP included preozonation, flocculation, and sedimentation, followed by  rapid sand filtering and chloramination. WTP- is situated  4 km upstream from the major wastewater treatment plant  (WWTP-) to ensure that the drinking water intake will  not be affected by the wastewater outlet (Figure 1). In late November 2010, the County Medical Office in  stersund received reports from several employers that  10%-20% of employees had gastroenteritis. The office  advised that patients with acute gastroenteritis be tested  for bacterial, viral, and protozoan pathogens. Among 20  patients from whom samples were obtained, 14 cases of  cryptosporidiosis were detected on November 26. The  local health advice line received numerous calls from  persons with gastroenteritis, most of whom lived within  the municipality (19). These facts indicated that the outbreak could be traced to the drinking water, and thus a boil-water advisory was issued for the municipality on  November 26. This study describes the outbreak investigation and outlines the extent of the outbreak, clinical  characteristics of persons infected, and risk factors for acquiring cryptosporidiosis. Methods Epidemiologic Investigation Electronic Survey To estimate the extent of the outbreak, the municipality published a questionnaire on its website during November 27- December 13, 2010. Persons in stersund who  582  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 1. Map of Lake Storsjn,  showing water currents (arrows)  and locations of wastewater  treatment plant, water treatment  plant,  and  contaminating  stream during Cryptosporidium  infection outbreak, stersund,  Sweden, 20102011.  C. hominis Infection Transmitted through Water Supply had gastrointestinal symptoms were encouraged to provide  information about day of onset, home address, and recent  food intake.  Written Questionnaire Two months after the outbreak began, we conducted  a retrospective cohort study, which included a random  sample of 1,524 persons living in stersund, to assess the  extent of the outbreak, clinical characteristics of infected  persons, and risk factors for acquiring cryptosporidiosis. We estimated the proportion infected among the population of stersund with a 3% margin of error (95% CI) by  assuming a 50% attack rate and a 70% response rate when  calculating the sample size. The patient questionnaire con- tained items on demographic characteristics, onset and oc- currence of possible symptoms of cryptosporidiosis, water  consumption, underlying diseases, and whether the WTP-  supplied water to the persons workplace. Residential WTP  supply was ascertained through population registers. Parents or guardians were asked to respond for children <15  years of age. A case-patient was defined as a person who  lived in stersund in mid-January 2011 and had had 3 ep- isodes of diarrhea daily and/or watery diarrhea with onset  after November 1, 2010, and before January 31, 2011. The  study was approved by the Research Ethics Committee of  the Faculty of Medicine, Ume University, Ume, Sweden. Microbiological Investigation Human Samples From November 1, 2010, through January 31, 2011,  fecal samples from inhabitants of stersund who had  acute gastroenteritis were tested for various pathogens. Cryptosporidium oocysts were analyzed by standard concentration techniques and modified Ziehl-Neelsen staining (20); enteric bacterial pathogens by standard  methods; noroviruses and sapoviruses by PCR; and Entamoeba spp. and Giardia duodenalis by conventional light microscopy. Environmental Samples During the outbreak, 163 samples of drinking water,  raw water, and wastewater were collected to trace the  source and monitor the presence of oocysts. Most water  samples were collected at or near WTP- and at WWTP- . However, as the outbreak spread to nearby regions,  sampling was also conducted at 14 other WTPs and 6  additional WWTPs. The municipality identified 4 differ- ent streams with high counts of Escherichia coli that may  have contaminated the raw water, and samples from those  streams were analyzed for Cryptosporidium. Also, as part  of a then-ongoing national survey regarding presence  of parasites in wastewater, 7 preoutbreak samples were   collected at WWTP-. The methods used are described  in the online Technical Appendix (wwwnc.cdc.gov/EID/ article/20/4/12-1415-Techapp1.pdf). Molecular Analysis/Typing In a subset of fecal samples, Cryptosporidium species  were determined by PCR restriction fragment-length poly- morphism analysis of the 18S rRNA gene (21). Species  were further characterized by sequence analysis of the 60- kDa glycoprotein (gp60) gene (22).  Oocysts in wastewater and stream water samples were  isolated from the contaminating debris by immunomagnetic  separation (IMS), and DNA was extracted (online Techni- cal Appendix). DNA was also extracted from oocysts that  had been obtained from 1 raw water sample and 1 drinking  water sample by use of Envirochek filters (Pall Life Science,  Ann Arbor, MI, USA) followed by IMS. Microscope slides  containing 113 oocysts from 4 raw water samples and 4  drinking water samples were sent to the Cryptosporidium  Reference Unit, Swansea, United Kingdom (online Techni- cal Appendix), where molecular analyses were performed. Statistical Analysis We conducted statistical analyses to test associations  between risk factors and duration of diarrhea after con- trolling for age, sex, and residence in the area served by   WTP-. Student t test was used to analyze differences in  attack rate and relapse rate. Relationships between risk fac- tors and clinical cryptosporidiosis as the outcome variable  were investigated by logistic regression. For dichotomous  predictors, odds ratios were used to measure associations  between clinical cryptosporidiosis and risk factors. Because  of overdispersion in the data, negative binomial regression  was applied to model the duration of infection in accor- dance with the case definition. Age and number of glasses  of water consumed per day were evaluated as continuous  variables. All statistical analyses were performed by using  SPSS software version 19 (SPSS Inc., Chicago, IL, USA).  A p value <0.05 was considered significant. Results Epidemiologic Investigation Electronic Survey Gastrointestinal symptoms were reported by 10,653  persons over a period of 2.5 weeks, confirming the large  outbreak in the city and contamination of the drinking  water (Figure 2). The number of cases of gastrointestinal  illness increased from mid-November and peaked on No- vember 29, three days after the boil-water advisory was is- sued. Thereafter, the number of new cases reported per day  rapidly declined.   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  583 RESEARCH Written Questionnaire Questionnaires were distributed by mail to 1,524 addressees; 10 persons had moved, and 6 were unable to  respond. Of the remaining 1,508, a total of 1,044 (69.2%)  responded: 481 men (46.1%) and 563 women (53.9%)  (median age 44 years Diarrhea[range 098 years])(Table 1). The  response rate was highest for women 6069 years of age  (90.0%) and lowest for men 2029 years (43.8%), and  45.2% (95% CI 42.1%48.3%) of all the responders met  the case definition criteria. When the rate of 45.2% was  applied to the total population of stersund (59,500),  results indicated that 27,000 (95% CI 25,04928,738)  inhabitants contracted clinical cryptosporidiosis during  the survey period. The attack rate decreased with age  (p<0.0001; Table 1, Figure 3), was highest (58.0%) for  persons 2029 years of age and lowest (26.1%) for per- sons >69 years of age (Table 1), and was similar for men  and women. The attack rate was 52.2% for respondents  who lived and worked in areas served by the WTP- but  only 12.8% for inhabitants of stersund who neither lived  nor worked in areas served by that plant (p<0.0001; data  not shown). The most common symptoms among case- patients were episodes of diarrhea >3 times daily (89.0%),  watery diarrhea (84.3%), abdominal cramps (78.8%), fa- tigue (73.1%), nausea (63.9%), and headache (57.1%)  (Table 2). Diarrhea lasted a median of 4 days (range 151  days). Duration of diarrhea decreased significantly with  age (p<0.0001; Table 3, Figure 3), as did the incidence of  584  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Figure 2. Epidemiologic curve of data from the electronic survey (10,653 participants; light gray) and written questionnaire (434 participants;  dark gray) showing number of patients with suspected cases by date of onset of illness during Cryptosporidium infection outbreak,  stersund, Sweden, 20102011.   Table 1. Distribution of survey respondents and attack rate in Cryptosporidium infection outbreak, stersund, Sweden, 20102011  Age group, y  No. respondents (%)    Attack rate, %  All  Female  Male    All  Women  Men  p value  09  115 (67.3)  58 (67.4)  57 (67.1)    50.9  42.6  58.9  0.09  1019  117 (66.5)  58 (61.1)  59 (72.8)    47.2  55.6  38.5  0.08  2029  103 (48.8)  57 (53.8)  46 (43.8)    58.0  58.2  57.8  0.97  3039  110 (55.8)  58 (60.4)  52 (51.5)    52.8  51.9  53.8  0.84  4049  150 (66.7)  71 (70.3)  79 (63.7)    55.0  52.9  57.0  0.62  5059  145 (79.2)  85 (84.2)  60 (73.2)    42.1  45.1  37.9  0.40  6069  148 (89.2)  81 (90.0)  67 (88.2)    35.3  41.3  27.6  0.10  >69  156 (87.2)  95 (88.8)  61 (84.7)    26.1  24.4  28.8  0.57  Total  1,044 (69.2)  563 (72.0)  481 (66.3)    45.2  45.1  45.4  0.94       C. hominis Infection Transmitted through Water Supply fever, headache, nausea, vomiting, and fatigue (data not  shown). Recurrence of diarrhea after >2 days of normal  stools (defined as a relapse) was reported in 49.1% of the  cases, and >1 relapse occurred significantly more often  among women than men (p = 0.016; Table 4). Higher con- sumption of water and gluten intolerance were significant  risks for Cryptosporidium infection (Table 3). Chronic  intestinal disease (defined as inflammatory bowel dis- ease [IBD], lactose intolerance, or gluten intolerance) and  young age were significantly associated with more days  with diarrhea (Table 3). Microbiological Investigation Human Samples A total of 186 laboratory-confirmed cases of cryp- tosporidiosis related to the outbreak were reported to the  national surveillance system: 149 in Jmtland County and  37 in other counties. Genotyping identified C. hominis sub- type IbA10G2 in 37 samples. A representative sequence  has been deposited into GenBank under accession no.  KF574041. Analyses showed that the 149 Cryptospori- dum-positive samples from Jmtland County were negative  for other gastrointestinal pathogens. Environmental Samples Cryptosporidium oocysts were found in drinking  water and raw water samples collected at the WTP-  on November 27 and in all samples of WTP- drink- ing water, water from the distribution network, and raw  water from Lake Storsjn over the next 2 months (Table  5). The highest number of oocysts in drinking water (1.4  presumptive oocysts/10 L) was detected on December  12, 2010 (online Technical Appendix Figure 1. During  the outbreak, the average oocyst density in drinking wa- ter was 0.32/10 L in WTP- samples and 0.20/10 L in  samples from the distribution network. Densities in raw  water samples were generally higher: 0.23.1 oocysts/  10 L. In WWTP- wastewater, the pre-outbreak low den- sity (<200 oocysts/10 L), had increased to 1,800/10 L on  November 16, was highest at 270,000/10 L on Novem- ber 29, and then gradually declined to preoutbreak levels  from December 31 onward (online Technical Appendix  Figure 2). Oocysts were detected in 4 of 22 raw water samples  from other municipalities near Lake Storsjn but in only  1 drinking water sample from a WTP (online Technical  Appendix Table). All samples of untreated wastewater,  most samples of treated wastewater (11/18), and samples  from recipient water bodies (6/9) contained oocysts. Two  of the 4 investigated streams connected to Lake Storsjn    Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  585 Figure 3. Percentage of ill persons (A) and mean duration of  symptoms fulfilling the case definition (B), stratified by age group  during Cryptosporidium infection outbreak, stersund, Sweden,  20102011 . Error bars represent 1 SE. Table 2. Clinical characteristics of surveyed case-patients and noncase-patients in Cryptosporidium infection outbreak, stersund,  Sweden, 2010-2011  Symptom  No. positive answers/total no. respondents (%)*  All respondents, N = 972  Case-patients, n = 434  Noncase-patients, n = 538  Diarrhea, >3 stools/d  382/967 (39.5)  382/429 (89.0)  0/538 (0)  Watery diarrhea  343/945 (36.3)  343/407 (84.3)  0/538 (0)  Abdominal cramps  382/952 (40.1)  328/416 (78.8)  54/536 (10.1)  Fatigue  342/921 (37.1)  302/413 (73.1)  40/508 (7.9)  Nausea  301/931 (32.3)  253/396 (63.9)  48/535 (9.0)  Headache  267/920 (29.0)  232/406 (57.1)  35/514 (6.8)  Fever >38.0C  128/909 (14.1)  121/393 (30.8)  7/516 (1.4)  Muscle or joint aches  95/875 (10.9)  80/366 (21.9)  15/509 (2.9)  Vomiting  89/894 (10.0)  76/357 (21.3)  13/537 (2.4)  Eye pain  81/877 (9.2)  67/367 (18.3)  14/510 (2.7)  Bloody diarrhea  16/883 (1.8)  15/345 (4.3)  1/538 (0.2)  *Respondents who answered yes (case-patients) compared with those who answered no (noncase-patients) about whether they had experienced >3  episodes of diarrhea daily and/or watery diarrhea with onset after November 1, 2010.  Results on the basis of answers from 972 of 1,044 respondents.     RESEARCH contained oocysts (Table 5). The stream closest to WTP-  (Figure 1) had densities of 1,300 and 5,000 oocysts/10 L on  November 30 and December 2, respectively; this finding  could be explained by wastewater leaking from an apart- ment building into the storm water system, which was re- paired on December 3. Isolated DNA from 1 concentrate of raw water, sep- arated from other particulate matter by IMS, was suc- cessfully amplified at the 18S rRNA gene locus, and C.  hominis was determined by restriction fragment length  polymorphism and sequence analysis. Subtyping was not  possible because amplification of the gp60 gene failed.  Also, despite repeated attempts, we were unable to amplify  any DNA sequences from oocysts detected in raw water  and drinking water by microscopy and removed from mi- croscope slides. C. hominis IbA10G2 was identified in 2 samples from  the stream closest to WTP-, in 5 from untreated wastewa- ter at WWTP-, and in 4 from other WWTPs in Jmtland  County. No other Cryptosporidium species or subtypes  were detected in any of the analyzed samples. Discussion We describe a confirmed outbreak of Cryptosporidium  infection affecting at least 27,000 inhabitants of stersund,  Sweden, which represents the largest known outbreak in  Europe and the second largest worldwide after the Milwau- kee outbreak. The etiologic agent was detected in drinking  water, repeatedly over >2 months. Although Cryptosporid- ium spp. are occasionally found in untreated surface water,  to our knowledge, this is the first time this pathogen has  been detected in drinking water in Sweden. Three factors facilitated detection of the outbreak.  First, before the outbreak was recognized, alert staff at  the county laboratory suspected oocysts in wet smears of  unstained, concentrated fecal specimens and subsequently  confirmed the presence of Cryptosporidium spp. by modi- fied Ziehl-Neelsen staining, even though this analysis had  not been specifically requested. Second, data from the lo- cal health advice line indicated that most persons with gas- troenteritis resided within the city limits, which proved to  be crucial for the decision to issue a boil-water advisory.  Third, the electronic survey was a valuable tool for daily  monitoring of the epidemic curve and evaluating the effect  of the boil-water advisory. Previous research has demon- strated the benefits of event-based surveillance data and  website questionnaires in early detection and monitoring of  an outbreak (23,24). The distribution of symptoms among case-patients  with cryptosporidiosis in this study is comparable to ob- servations from other studies (6,17,25), except regarding  muscle or joint aches, which were reported less frequently  in stersund. Moreover, the median duration of diarrhea,  the level of attack rates in different age groups, and recur- rence rate of diarrhea correspond to findings in other out- breaks (6,14). We identified young age, amount of water consumed,  and number of infected family members as risk factors,  which agrees with results from other studies (26,27).  Also, gluten intolerance remained a risk factor after we  controlled for age, sex, and residence in the WTP area,  but this analysis was based on information from only 17  persons and hence should be interpreted with caution. The  mechanism by which gluten intolerance might constitute  a risk factor for cryptosporidiosis is unknown. Duration  of diarrhea was significantly associated with young age  and chronic intestinal disease. Exacerbation of IBD in  cryptosporidiosis patients has been documented (28), and  Cryptosporidium-induced loss of intestinal barrier func- tion has been suggested to mimic changes seen in IBD  (29). Additional studies are needed to clarify any long- term effects of Cryptosporidium infection and are being  undertaken in relation to the current outbreak. Molecular typing identified C. hominis IbA10G2 in  both human and environmental samples. This early iden- tification of nonlivestock-associated Cryptosporidium  586  Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014 Table 3. Risk factors for cryptosporidiosis and duration of infection in Cryptosporidium infection outbreak, stersund, Sweden,   2010 2011*  Risk factor  Infection  Duration, p value  Adjusted OR (95% CI)  p value  Age, continuous  0.99 (0.980.99)  <0.0001  <0.0001  Chronic intestinal disease  1.86 (0.952.63)  0.08  <0.01  Chronic underlying disease#  1.15 (0.731.8)  0.55  0.59  Gluten intolerance  4.06 (1.2413.29)  0.02  0.05  Lactose intolerance  1.40 (0.792.46)  0.25  <0.01  No. additional family members with cryptosporidiosis  1.99 (1.702.33)  <0.0001  NA  No. glasses of water consumed daily  1.07 (1.031.11)  <0.0001  0.07  No. persons in household  0.98 (0.871.07)  0.54  NA  Peptic ulcer or medication  1.26 (0.722.22)  0.42  0.43  Smoking  1.01 (0.581.75)  0.98  0.40  *OR, odds ratio, adjusted for age, sex, and residence in the water treatment plant area; NA, not applicable.  Participants with watery diarrhea and/or >3 episodes of diarrhea daily were defined as having cryptosporidiosis.  Duration (i.e., time fulfilling the case definition).  Defined as inflammatory bowel disease, lactose intolerance, or gluten intolerance.  #Defined as cancer, rheumatic disease, cardiac failure, asthma, chronic obstructive pulmonary disease, or diabetes. C. hominis Infection Transmitted through Water Supply isolates facilitated the outbreak investigation by indicating that the cause was contamination of surface water by human sewage rather than contamination from an animal source (4,30). C. hominis IbA10G2 is reported to be highly  virulent; is excreted in high numbers in feces (1,31,32);  and is the most commonly identified subtype in waterborne  cryptosporidiosis outbreaks, including that in Milwaukee  (3,30,33,34). These characteristics, along with occurrence  of the outbreak in a population that may have been par- ticularly susceptible because of limited previous exposure,  contributed to the high attack rate (35,36). Although the infectious dose for Cryptosporidium in- fection is low, the oocyst densities in the stersund drink- ing water (maximum 1/10 L) cannot readily explain the  high attack rate, even if the low recovery rate is taken into  account. Densities may have been higher at the onset of the  outbreak because of a surge of oocysts in the inlet before  sampling, and secondary household transmission could  have contributed to some of the cases. However, similar  low numbers of oocysts have been detected in drinking wa- ter samples in other outbreaks (26,37). The level of recov- ery efficiency of the methods used in the outbreak required  analysis of at least 100 L of water to identify the low level  of Cryptosporidium contamination, which agrees with find- ings reported by other investigators (26). Recovery studies were not performed during the acute  phase of the stersund outbreak, which underscores the  uncertainty of extrapolating the numbers of oocysts de- tected in raw and drinking water to the actual density of  oocysts (38). Moreover, no reliable assays to test viability  and infectivity of oocysts are available (1). Other limita- tions of the present study include potential response bias  in the electronic survey and the mailed questionnaire (39).  Moreover, we could not assess the contribution of second- ary transmission to the attack rate or ascertain the number  of subclinical cases by serologic testing. Several possible factors could explain Cryptospo- ridium contamination of the drinking water. In the rou- tine bacteriologic analysis performed weekly at WTP-,  E. coli densities were 10 times greater than the average  level on 3 occasions a few weeks before the outbreak (H.  Dahlsten, pers. comm.), which implies abnormally high  fecal contamination of the source water. Furthermore,  Cryptosporidium oocysts were detected repeatedly in  both raw and drinking water for months after the outbreak  peaked, which illustrates the environmental persistence  of oocysts and/or continuing contamination. Survival of  the oocysts in Lake Storsjn was probably prolonged be- cause the outbreak occurred in winter when the lake was  covered with ice. The municipality of stersund made     Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  587 Table 5. Presence of Cryptosporidium oocysts in environmental samples collected in stersund, Sweden, November 27, 2010 March  22, 2011*  Sample type  No.  samples  No. positive  samples  Analyzed  volume, L  Presumptive  no. oocysts,  minmax/10 L  Confirmed no.  oocysts,  minmax/10 L  Time span for positive  samples  Raw water  18  10  100  0.23.1  0.10.7  2010 Nov 272011 Feb 9  Drinking water, WTP-  7  7  8001,500  0.0471.4  0.021.3  2010 Nov 272011 Jan 20  Drinking water, distribution  network  9  9  8001,400  0.0630.36  0.050.05  2010 Nov 292011 Jan 31  Wastewater, untreated  21  13  0.05  200270,000  160,000  2010 Nov 292011 Feb 17  Wastewater, treated  15  14  0.250.3  3021,000  3010,000  2010 Dec 12011 Jan 24  Recipient (Lake Storsjn)  14  8  910  221  118  2010 Nov 292011 Mar 22  Connected streams  8  5  210  1,3005,000  9503,500  2010 Nov 30Dec 14  Other  10  2  1017  13  13  2010 Nov 302011 Jan 17  Total  102  68    0.047270,000  0.02160,000  2010 Nov 272011 Mar 22  *Min, minimum; max, maximum; WTP-, water treatment plantstersund.   Details are available in Technical Appendix Figures 1 and 2, wwwnc.cdc.gov/EID/article/20/4/12-1415-Techapp1.pdf.  These samples consisted of 30-mL aliquots from every 5060 m3 of wastewater produced over 24 h.  Not possible to determine the lowest density by microscopy because of substantial background material in the concentrated water sample.  Samples from sources, such as swimming pools, water used to flush the distribution network, and sediment from fire hydrants.    Table 4. Distribution of respondents and relapse of diarrhea among surveyed case-patients in the Cryptosporidium infection outbreak,  stersund, Sweden, 20102011  Age group, y    All relapses, %  1 Relapse, %     >1 Relapse, %  Female  Male  p value    Women  Men  p value  09  68.5  50.0  43.8  0.66    22.7  21.9  0.94  1019  48.9  20.7  50.0  0.04    20.7  10.0  0.30  2029  40.4  22.6  19.2  0.76    22.6  15.4  0.50  3039  47.3  25.9  32.1  0.63    29.6  7.1  0.03  4049  51.3  27.8  36.4  0.42    25.0  13.6  0.21  5059  47.4  22.2  23.8  0.89    25.0  23.8  0.92  6069  47.8  22.6  20.0  0.85    29.0  20.0  0.52  >69  35.3  15.0  35.7  0.20    15.0  7.1  0.50  Total  49.1  25.4  33.5  0.07    24.1  15.0  0.016      RESEARCH considerable efforts to trace the sources of Cryptosporid- ium contamination, and tentatively identified 2 streams,  1 of which was located closer to (upstream of) the raw  water intake (Figure 1) and had higher densities of oo- cysts. However, we could not establish whether the initial  input of oocysts to Lake Storsjn and the raw water intake  had actually come from these streams, or whether it re- sulted from the outbreak itself. Perhaps these 2 streams  contributed to a transmission cycle in which infectious  persons were shedding oocysts into leaking wastewater  that reached the raw water intake. Because only C. homi- nis IbA10G2 was identified in environmental samples, we  suggest that the outbreak was caused by a single common  source of contamination, although this hypothesis could  not be definitively demonstrated. Failure of the WTP- and onset of the outbreak has sev- eral plausible explations. To our knowledge, no posttreatment  contamination or extensive failures in the treatment processes  occurred, and routine tests of the drinking water showed no  increased levels of fecal indicator bacteria. The WTP- had  2 microbiological barriers (ozonation and chloramination) as  recommended by the drinking water regulations in Sweden  for surface waterworks, but these barriers were simply inad- equate to remove or inactivate the Cryptosporidium oocysts  in the raw water. The long-term solution to reduce infective  parasites in stersund was to install a UV water disinfection  system, which was done after the outbreak in December 2010.  In addition, pipes were repeatedly flushed, and and further  sampling was conducted to verify that no potentially viable  oocysts remained in the distribution network. Previous research has suggested that analysis of Cryp- tosporidium in wastewater can aid in early detection of an  outbreak (40). In stersund, the number of Cryptospo- ridium oocysts in influent wastewater increased slightly 10  days before the boil-water advisory (1,800 oocysts/10 L),  which indeed implies that monitoring the level of oocysts  in influent wastewater might facilitate early detection of an  ongoing outbreak, although the cost of such an approach  would render it impractical. Six months after the outbreak in stersund, another  waterborne outbreak of C. hominis IbA10G2 infection  occurred in the city of Skellefte, 450 km northeast of  stersund, possibly because persons from that city had  visited stersund during the outbreak there and had sub- sequently spread Cryptosporidium oocysts on their return  to Skellefte. In Sweden, recommendations to prevent out- breaks of parasites include identifying and limiting sources  of contamination of raw water in combination with sam- pling (100-L volumes). The awareness of parasites as a  probable cause of waterborne outbreaks has increased tre- mendously in this country since these outbreaks, and many  WTPs have evaluated the efficiency of their current barri- ers, for example, by quantitative microbial risk assessment. This study has documented the largest outbreak of  waterborne cryptosporidiosis in Europe, affecting 27,000  persons. C. hominis subtype 1bA10G2 was identified in  clinical samples and in wastewater. Low levels of oocysts  were repeatedly detected in drinking water for >2 months.  Our results emphasize the value of assessing microbial  risks in raw water and using multiple barriers in WTPs to  substantially reduce or inactivate all groups of microorgan- isms, including parasites such as Cryptosporidium spp. Acknowledgments We thank Joyce Eriksson, Tomas Nilsson, Jessica Ns, and  Lill Welinder for their excellent technical assistance. We also  thank Johan Wistrm for invaluable intellectual comments.  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Prevalence  and distribution of Cryptosporidium and Giardia in wastewater  and the surface, drinking and ground waters in the Lower Rhine,  Germany.  Epidemiol  Infect.  2013;141:921.  http://dx.doi. org/10.1017/S0950268812002026 Address for correspondence: Micael Widerstrm, Department of Clinical  MicrobiologyClinical Bacteriology, Ume University, Ume 90185,  Sweden; email: micael.widerstrom@jll.se   Emerging Infectious Diseases  www.cdc.gov/eid  Vol. 20, No. 4, April 2014  589 
",What was the alert of the event?,"{'answer_start': [6571], 'text': ['received numerous calls from  persons with gastroenteritis']}"
22,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What type of samples were analyzed?
","{'answer_start': [1236], 'text': ['stool samples']}"
29,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
",What did the local authorities investigate?,"{'answer_start': [1203], 'text': ['microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples']}"
14,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
",What were the first steps of investigation?,"{'answer_start': [519], 'text': ['case ascertainment and descriptive epidemiology']}"
12,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What is the date of the event?
","{'answer_start': [14], 'text': ['July 2006']}"
21,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What is the location of the event?
","{'answer_start': [142], 'text': ['Taranto, Apulia']}"
8,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","How was the event first detected?
","{'answer_start': [25], 'text': ['an unusually high number of patients with acute diarrhoea were reported']}"
30,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","How many people were ill?
","{'answer_start': [6325], 'text': ['166 cases']}"
11,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What are the pathogens?
","{'answer_start': [4700], 'text': ['norovirus and  11 (25%) for rotavirus']}"
26,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What are the symptoms?
","{'answer_start': [6268], 'text': ['fever >= 38C, headache, vomit, abdominal pain, nausea']}"
5,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What is the event?
","{'answer_start': [38], 'text': ['high number of patients with acute diarrhoea ']}"
8,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What is the duration of the event?
","{'answer_start': [422], 'text': ['between July and October 2006']}"
13,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What are the first steps of mitigation?
","{'answer_start': [7230], 'text': ['extra  chlorination treatment']}"
5,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What type of samples were examined?
","{'answer_start': [1326], 'text': ['environmental samples']}"
31,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
","What was the age of the affected people?
","{'answer_start': [2425], 'text': ['mean age was 25']}"
26,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
",What is the source of contamination?,"{'answer_start': [7155], 'text': ['drinkable tap water contaminated with (at least) rota- and noroviruses']}"
28,Contamination Question Answering,"At the end of July 2006, an unusually high number of patients with acute diarrhoea were reported by the accident and emergency departments in Taranto, Apulia. Subsequently, a field  investigation was conducted jointly by the Apulia Regional Epidemiological Observatory and the  Regional Reference Laboratory in Bari, and the Epidemiological Department of Taranto Local  Health Unit. The outbreak investigation carried out between July and October 2006, involving hospitals in the  whole province of Taranto, included a case ascertainment and descriptive epidemiology. A case was defined as a patient with  diarrhoea (at least three loose or liquid stools in a day) and one or more of the following  symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea [1,2]. Five out of six hospitals in the province of Taranto provided information on patients with  acute gastroenteritis. Data were collected retrospectively for the period between May and  July and prospectively for August and September 2006. In addition, the special medical facilities set up for tourists in the summer season (June-August) in the province of Taranto  were also asked to report cases. The outbreak investigation included microbiological investigation of stool samples of hospitalized patients. It also included microbiological investigation of environmental samples (including tap water, sea water and  shellfish) [1-4].  G     Case control study performed between 1 August and 15 September 2006 in order to  identify the possible sources of infection. From 1 May to 30 September 2006, a total of 2,860 patients with gastroenteritis symptoms were  either admitted to hospital or seen by the hospitals outpatient accident and emergency units.  This significantly exceeded the number reported in the same period in 2005, when a total of 586  patients with gastroenteritis were treated by the same hospitals. The epidemic curve is shown in  Figure 1.  Figure 1. Number of patients with gastroenteritis seeking hospital care, by week. Taranto  province, 1 May-30 September, 2005 and 2006 The first peak in incidence was observed at the end of June (26 week of the year), followed by a  second peak at the end of July (weeks 29 and 30). The number of patients with gastroenteritis  seeking hospital care decreased in the following weeks. By mid-September, the number of cases  per week was similar to that seen in the same period of 2005. Patients mean age was 25 years; 19% of the cases were under 5 years of age, 16% were 5 to 15  years old, and 65% were above 15 years of age. Incubation time was not calculated because it  was not possible to determine the exact time of exposure.  Incidence by town of residence was highest in the city of Taranto (9.5 cases per 1,000  inhabitants) (Figure 2).  http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (2 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Figure 2. Number of patients with gastroenteritis seeking hospital care, by town of residency per  1,000 inhabitants. Taranto province, 1 May-30 September 2006 Data collected by the tourist medical facilities in Taranto province showed a total of 361 cases of  acute gastroenteritis, significantly more than a year before. Hence the same trend was observed  as in the case of hospital data.  Microbiological analysis  A total of 70 stool samples from patients affected by the outbreak were collected and analysed.  Results by age group are reported in Table 1. Table 1. Stool samples collected from patients and tested by the Regional Reference Laboratory  (U.O.C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Age Number of  samples  Rotavirus () Norovirus (*) < 15 51 32 (62%) 19 (37%) >= 15 7 1 (14%) 4 (57%) Unknown 12 1 (8%) 5 (41%) Total 70 34 (48%) 28 (40%)   () Nested PCR in VP7 region  (*) Nested PCR in the polymerase gene  Stool samples were also examined with respect to gastrointestinal bacteria and parasites. No  samples examined were positive for the entire range of pathogens tested.  Further genotyping of the samples is currently being done. Environmental samples, systematically collected for microbiological analyses, were tap water from  the water distribution system across the whole area affected by the outbreak, sea water and  shellfish. The water samples were collected at the local waterworks, from major water pipelines  and wells, and from tap water in pubs.  No faecal indicator bacteria and endotoxins were detected in the environmental samples of tap  water collected in Taranto city. Of 44 samples tested, four (9%) were positive for norovirus and  11 (25%) for rotavirus (Table 2). The tests were performed using molecular techniques. http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (3 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 Table 2. Drinkable tap water samples collected and tested  Regional Reference Laboratory (U.O. C. Igiene, Azienda Ospedaliera Policlinico), Bari, August  September 2006  Date Number of  samples  Norovirus Rotavirus Both 31.07.2006 2 1 1 0 2.08.2006 3 0 2 0 8-9.08.2006 3 0 0 0 12.09.2006 4 1 1 0 14.09.2006 2 0 0 0 18-19.09.2006 8 1 3 1 12.10.2006 6 1 2 0 19.10.2006 13 0 2 0 27.10.2006 3 0 0 0 Total 44 4 (9%) 11 (25%) 1 (2%) Molecular profiles of rotavirus and norovirus identified in some tap water samples were the same  as the ones found in some patients stool samples. Sequence analysis showed the new norovirus  strain GGII.4 2006a and rotavirus genotype G9. The laboratory investigations, however, are still  ongoing and more results are expected in the future.  Of 12 sea water samples tested, four (33%) were positive for norovirus and one (8,3%) for  rotavirus.  No shell fish samples were positive for bacteria or viruses.  Case control study  A case control study was performed in order to find an association between the occurrence of  gastroenteritis and the exposure to one or more risk factors.   A case was defined as a patient with at least 3 loose or liquid stools in a day and one or more of  the following symptoms: fever >= 38C, headache, vomit, abdominal pain, nausea.   166 cases were selected among patients treated at the accident and emergency departments of  the hospitals in Taranto province, in the period between 1 August and 15 September 2006. The  control group consisted of 146 non-hospitalised healthy individuals who during the study period  were resident in the same area as the case patients. Cases and controls were age-matched. A standard questionnaire was used for the interview.  Risk factors which were shown to be significantly associated with the onset of acute diarrhoea/ gastroenteritis were the use of tap water (OR= 2; 95% CI: 1,23-3,36), and the use of water of  uncertain origin in the 72 hours before the onset of the symptoms (OR= 3,9; 95% CI: 1,41- 10,54). The epidemiological investigation and the laboratory tests showed that the possible source of  infection was the drinkable tap water contaminated with (at least) rota- and noroviruses. An extra  chlorination treatment for household water supplies was therefore performed starting from the  34th week of the year in order to stop a possible contamination of the water.  Systematic technical and microbiological investigations of the pipelines and wells of the water  distribution system did not reveal the source of contamination even though technical problems at  the local chlorination treatment facilities could not have been excluded.   http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (4 di 5)19/05/2008 10.16.21 http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 To date, the outbreak of viral gastroenteritis described in this paper is probably the largest one  associated with drinking tap water in Italy. Acknowledgements  A. Mincuzzi, T. Battista, R. Mongelli, M.T. Balducci, C. Ladalardo, A. Fusco, S. Tafuri, A.  Panebianco, F. Fortunato, A. Arbore, L. Lamarina (Department of Biomedical Science and Human  Oncology, Hygiene Section, University of Bari - Apulia Regional Epidemiological Observatory); A.  Pesare, S. Minerba, G. Grassi, M. Rollo, D. Zuppiroli (Taranto Local Health Unit); F. Portincasa, P.  Montemurro, G. Vitucci (Apulia Water Distribution Company Ente Acquedotto Pugliese) References: 1.  Chironna M, Prato R. Lopalco PL, Germinario C, Sallustio A, Barbuti S, Quarto M. Norovirus GI e GII in corso  di epidemia di gastroenterite acuta associata al consumo di molluschi bivalvi in Puglia. Rapporti ISTISAN  2003; 3/C5: 39.  2.  Prato R, Lopalco PL, Chironna M, Barbuti G, Germinario C, Quarto M. Norovirus gastroenteritis general  outbreak associated with raw shellfish consumption in South Italy. BMC Infectious Diseases, 2004; 4: 37.  3.  Liang JL, Dziuban EJ, Craun GF, Hill V, Moore MR, Gelting RJ, Calderon RL, Beach MJ, Roy SL. Surveillance  for waterborne disease and outbreaks associated with drinking water and water not intended for drinking,  United States, 2003-2004. In: Surveillance Summaries, MMWR, 2006; 55: 31-58.  4.  Boccia D, Tozzi AE, Cotter B, Rizzo C, Russo T, Buttinelli G, Caprioli A, Marziano ML, Ruggeri FM.  Waterborne Outbreak of Norwalk-Like Virus Gastroenteritis at a Tourist Resort, Italy. Emerging Infection  Diseases, 2002; 8(6):563-568.  back to top    Back to Table of Contents  Next   To top |   Recommend this page  Disclamer:The opinions expressed by authors contributing to Eurosurveillance do not necessarily reflect the opinions of the European Centre for Disease Prevention and Control (ECDC) or the Editorial team or the institutions with  which the authors are affiliated. Neither the ECDC nor any person acting on behalf of the ECDC is responsible for the use which might be made of the information in this journal.   Eurosurveillance [ISSN] - 2008 All rights reserved      http://www.eurosurveillance.org/ViewArticle.aspx?PublicationType=W&Volume=12&Issue=16&OrderNumber=1 (5 di 5)19/05/2008 10.16.21 View publication stats View publication stats 
",What were the associated pathogens of concern?,"{'answer_start': [5479], 'text': ['rotavirus and norovirus ']}"
22,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
",What symptoms did the people had?,"{'answer_start': [5856], 'text': ['chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%).']}"
19,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What type of samples were analyzed?
","{'answer_start': [838], 'text': ['stool samples']}"
6,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
",What were the first steps of investigation?,"{'answer_start': [249], 'text': ['a message on a social media website asked racers to report any symptoms by email']}"
32,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What is the initial cause of the event?
","{'answer_start': [1083], 'text': ['human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risk']}"
34,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What is the date of the event?
","{'answer_start': [104], 'text': ['summer of 2015']}"
8,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What is the location of the event?
","{'answer_start': [89], 'text': [' France']}"
8,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
",What pathogen was connected to the outbreak?,"{'answer_start': [6129], 'text': ['Shigella sonnei)']}"
10,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","How was the event first detected?
","{'answer_start': [1370], 'text': ['a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG']}"
19,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","How many people were ill?
","{'answer_start': [597], 'text': ['1,264 adults ']}"
6,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What is the attack rate?
","{'answer_start': [4819], 'text': ['attack rate: 16%']}"
11,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What are the pathogens?
","{'answer_start': [889], 'text': ['norovirus genogroup I and genotype 2']}"
14,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [6421], 'text': ['counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL)']}"
30,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What are the symptoms?
","{'answer_start': [5450], 'text': ['vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and feve']}"
27,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What is the event?
","{'answer_start': [6889], 'text': ['A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015']}"
29,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What are the initial steps of investigation?
","{'answer_start': [397], 'text': ['a retrospective cross-sectional study was conducted through an interactive questionnaire']}"
27,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What are the first steps of mitigation?
","{'answer_start': [4440], 'text': ['provided recommendations on measures to prevent secondary spread during a press conference ']}"
17,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
",What was the outbreak investigation?,"{'answer_start': [120], 'text': ['An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak']}"
34,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What measures were taken to prevent the event?
","{'answer_start': [1202], 'text': ['Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers']}"
27,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
","What was the age of the affected people?
","{'answer_start': [5348], 'text': ['The mean age of adult respondents was 33 years (range: 18-61 years)']}"
15,Contamination Question Answering,"An acute gastroenteritis (AG) outbreak occurred among participants in an obstacle race in France in the summer of 2015. An investigation in two phases was conducted to identify the source of infection and document the extent of the outbreak. First, a message on a social media website asked racers to report any symptoms by email to the Regional Health Agency of Provence-Alpes-Cte dAzur. Second, a retrospective cross-sectional study was conducted through an interactive questionnaire for all participants, followed by an analytical study of potential risks factors. Of 8,229 persons registered, 1,264 adults reported AG resolved within 48 hours. Of adults who reported AG, 866 met the case definition. Age group, departure time and ingestion of mud were associated with AG. Twenty stool specimens tested negative for bacteria. All four stool samples tested for viruses were positive for norovirus genogroup I and genotype 2. No indicator bac- teria for faecal contamination were found in drinking water but muddy water of ponds tested positive. The outbreak was possibly caused by human-to-human transmission of a norovirus introduced by one or more persons and transmitted through contaminated mud. Risks related to similar races should be assessed and recommendations be proposed to raise awareness among health authorities and organisers. On 22 June 2015 at 16:00, a hospital near Nice alerted the Regional Health Agency of Provence-Alpes-Cte dAzur (ARS PACA) of 22 patients with AG after participation in an obstacle race, in the south of France. On a social media website, many other participants reported also suffering from similar symptoms. An investigation was immediately conducted in order to identify the source of infection and document the extent of the outbreak. Methods The ARS PACA, responsible for the outbreak inves- tigation and implementation of control measures, requested support of the Regional Office of the French Public Health Agency (Cire Sud). Epidemiological investigation The investigation of the outbreak was conducted in two phases. The first phase started immediately, upon receipt of the outbreak alert, on 22 June 2015. ARS PACA and Cire Sud sent a message on a social media website informing the participants of the obstacle race that an investigation was conducted and asked them to report any recent or current gastrointestinal illness by email to a dedicated address of ARS. This information was also relayed by the organisers of the race and the local press. The second phase, aimed at collecting additional information, was conducted retrospectively through an interactive application, Voozanoo (a secure web-based platform for hosting personal health data) including sections on socio-demographic characteristics, presence of symptoms or not, and sections on potential exposures (catering, means of contact with mud). This short questionnaire (available from the authors upon request) was intended for all participants of the obstacle race, whether or not they had clinical signs of AG. On 30 June, the company that had organised the event sent the Internet link for this survey by email in a news- letter to all the participants of the obstacle race. Cross-sectional descriptive studies were conducted in two phases, and were followed by an analytical study of the potential risks factors (in the second phase). A case of AG was defined as a racer in the obstacle race that took place on 20 June, with self-reported gastrointestinal illness (vomiting and/or diarrhoea) associated or not with other symptoms within eight days from the race. A secondary case of AG was defined as a person who did not participate in the obstacle race as racer, with gastrointestinal illness following at least 24 hours after a contact with a case of AG among racers. We recommended all laboratories to test stool specimens from the racers for Salmonella, Shigella, Campylobacter and Yersinia, and to send stool specimens to the National Reference Laboratory (NRL) for Enteric viruses in Dijon in order to test for norovirus, sapovirus, rotavirus, adenovirus and astrovirus. These samples were tested by a laboratory in Lyon. Water samples were tested for Campylobacter and norovirus by the Laboratory for Hydrology of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES,) in Nancy. The University Laboratory of Pharmacy in Lyon tested the specimens for species of Naegleria [10]. We provided recommendations on measures to prevent secondary spread during a press conference organised on 22 June, through a weekly report of the Cire Sud, on the ARS PACA website, and we posted prevention messages on a social media website. the outbreak investiga- tion was published on the social media website. Among the respondents, 1,300 AG cases were reported: 1,264 adults (attack rate: 16%; 1,264/7,804) and 36 secondary cases (not included in this analysis). Phase 2 was conducted from 30 June to 27 July and a total of 748 questionnaires were completed (for 745 adults and 3 children). Among the participants who filled out the questionnaire, more than half (404/748; 54%) did it the day the newsletter came out and one third (247/748; 33%) the day after. There were 375 AG cases and 373 non cases. Secondary cases reported by respondents rose to a total of 177 cases, not included in this analysis. The mean age of adult respondents was 33 years (range: 18-61 years). The most common symptoms besides vomiting and/or diarrhoea, were abdominal cramps (369/866; 43%) and fever (354/866; 41%). Those symptoms were over or being spontaneously resolved in 48 hours. In phase 2, 69% of participants notified being ill (513/745) and among them, 73% met the case definition (375/513); of these, 67% (251/375) presented fever and 43% (161/375) other digestive symptoms. The other symptoms were non-specific, such as chills (215/375; 57%), headaches (101/375; 27%), asthenia (322/375; 86%), and muscle ache (262/375; 70%). Microbiological investigations We obtained the results of 20 stool samples. Results of bacteriological testing were negative for all samples, except one (positive for Shigella sonnei). Among the four specimens sent to the NRL for enteric viruses, all were positive for norovirus genogroup I and genotype 2 (GI.2). Of the environmental water specimens (n=5) taken from five ponds on 23 June, all were found contaminated by aerobic microorganisms at 36 C (with counts ranging from 86 to 3,200,000 UFC/100 mL) and 22 C (with counts ranging from 2,500 to 1,400,000 UFC/100 mL), indicating bacterial contamination. All specimens were negative for Salmonella, Campylobacter, Enterovirus, V. cholerae and V. parahemolyticus. All environmental samples were positive for Naegleria spp. (with cells ranging from 400 to 280,000/L), but the pathogenic species N. fowleri was not detected. Norovirus geno- group I and II were not detected. A large AG outbreak occurred among the participants of obstacle race in the department of Alpes-Maritimes, France, on 20 June 2015. Of 7,804 adult participants, 1,264 were ill and 866 met the case definition of AG. This outbreak occurred from 20 to 25 June and the epidemiological curves during two different phases of the outbreak investigation were characteristic of a point-source outbreak. The epidemiological investigation enabled us to identify mud ingestion as the main risk factor of developing AG; no other source of infection was identified. Several arguments support a common source outbreak of human origin related to the ingestion of contaminated mud. 
",What is the source of contamination?,"{'answer_start': [7469], 'text': ['common source outbreak of human origin related to the ingestion of contaminated mud']}"
8,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What type of samples were analyzed?
","{'answer_start': [706], 'text': ['water samples']}"
9,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

",What caused the event?,"{'answer_start': [4886], 'text': ['combination of a technical and a human error at a local sewage treatment facility,']}"
6,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

",With what symptoms they were presented?,"{'answer_start': [2892], 'text': ['diarrhoea, vomiting and/or abdominal pain/cramps with fever.']}"
29,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

",What did the local authorities investigate?,"{'answer_start': [6645], 'text': ['Geographical information systems were used to define the contaminated area']}"
24,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What is the date of the event?
","{'answer_start': [13], 'text': ['January 2007']}"
12,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What is the location of the event?
","{'answer_start': [45], 'text': ['Denmark']}"
27,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","How was the event first detected?
","{'answer_start': [75], 'text': ['several complaints from citizens']}"
31,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","How many people were ill?
","{'answer_start': [3232], 'text': ['140 cases']}"
28,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","How many people were hospitalized?
","{'answer_start': [4086], 'text': ['Four patients ']}"
20,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What are the pathogens?
","{'answer_start': [1106], 'text': ['coliform counts and�Escherichia coli)']}"
20,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What are the symptoms?
","{'answer_start': [128], 'text': ['diarrhoea and vomiting ']}"
19,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What are the initial steps of investigation?
","{'answer_start': [706], 'text': ['water samples for microbiological and chemical analyses were systematically collected from the water distribution system']}"
29,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What are the first steps of mitigation?
","{'answer_start': [322], 'text': ['prohibited any use of the water - except for toilet flushing']}"
24,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What type of samples were examined?
","{'answer_start': [2673], 'text': ['Stool samples']}"
31,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What did the authorities do to restore the system?
","{'answer_start': [5959], 'text': ['the distribution system was subsequently disinfected by chlorination']}"
11,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

","What steps were taken to restore the problem?
","{'answer_start': [5750], 'text': ['Flushing of the area�s distribution system was initiated immediately and sustained for several weeks']}"
24,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

",What did the authorities do to mitigate the event?,"{'answer_start': [538], 'text': ['The citizens in the area were warned by the police and through radio broadcasts']}"
30,Contamination Question Answering,"On Monday 15 January 2007, a municipality in Denmark received the first of several complaints from citizens who reported severe diarrhoea and vomiting over the weekend. Over the same period, the drinking water in many houses was reported to be discoloured and of unusual smell and taste. The local authorities immediately prohibited any use of the water - except for toilet flushing - in the entire area supplied with untreated drinking water from the local waterworks, which involved 5,802 citizens and a number of companies (Figure 1). The citizens in the area were warned by the police and through radio broadcasts.
To reveal the nature and the geographical spread of the suspected water contamination, water samples for microbiological and chemical analyses were systematically collected from the water distribution system across the whole area supplied from the local waterworks. The water samples were collected at the waterworks itself, from major water pipelines and wells, and from tap water in private houses and companies. High concentrations of faecal indicator bacteria (primarily presumptive coliform counts and�Escherichia coli) and endotoxins in the water samples indicated a massive faecal contamination of a part of the water distribution system, while other parts of the distribution system appeared not to be affected. On the basis of the geographical distribution of indicator bacteria, and the technical information about directions of the water flow in the different sections of the water distribution system, the area suspected to be contaminated was systematically reduced step by step during the next days.
Based on the analyses of 530 water samples collected at 200 different sites, the area finally considered to be affected by the water contamination was defined on 26 January 2007 (indicated with a red line in Figure 1). This area comprised 177 households with 450 residents and several companies, among which six dealt with food. Restrictions on water use were maintained in this area, while the water was released for normal use in the area that was not considered to be contaminated.
Gastrointestinal illness
A line-list of patients with gastrointestinal illness associated with the water contamination was established on the basis of notifications from general practitioners, enquiries made to the medical health officer, patients seeking advice from the emergency medical service, and patients contacting an ad hoc telephone �hotline� established by the local authorities. Additional information was collected during a house-to-house questionnaire survey conducted on 16 January among 20 households in the most severely affected street. Stool samples were examined at the Department of Bacteriology, Mycology and Parasitology, and the Department of Virology, Statens Serum Institut, Copenhagen. A case of acute gastroenteritis was defined as a person with diarrhoea, vomiting and/or abdominal pain/cramps with fever. To verify whether reported cases met the case definition, and to confirm the geographical extent of gastrointestinal illness associated with the water contamination, patients on the line-list were contacted by telephone and/or postal questionnaires.
By the end of February 2007, 140 cases had been registered: 110 were residents of the area that was judged to be contaminated on the basis of the environmental investigations, 12 were shoppers or employees at the food companies in the area, and 18 affected people came from outside the contaminated area. The epidemic curve for cases among residents in the contaminated area with known date of illness onset is shown in Figure 2. No new cases in the contaminated area were registered after 24 January.
Cases were largely confined to the contaminated area. A total of 24% of the residents of the contaminated area were registered with gastrointestinal illness, compared with 0.3% in the other sections of the waterworks� supply area (relative risk 73; 95% CI 44-127). From the most severely affected street in the contaminated area, 43% of residents were reported to have fallen ill. Four patients were temporarily admitted to hospital.
Microbiological results
By the end of February 2007, stool samples from 139 patients affected by the outbreak (including 99 patients who met the case-definition criteria) had been examined with respect to gastrointestinal bacteria, viruses and parasites. Among these, 77 patients (43 cases) had one or more samples that tested positive, including 23 patients with 2-5 different pathogenic gastrointestinal organisms (Table). Not all samples were tested for the entire range of pathogens identified. Further microbiological testing and genotyping of the samples are being undertaken.
Technical assessment and intervention
Technical and microbiological investigations of the water indicated that the most probable cause of the contamination was the combination of a technical and a human error at a local sewage treatment facility, which allowed at least 27 m3�of partially filtered waste water to enter into the drinking water system in the period between 12 and 14 January 2007. The two pipelines were separated, and the exact circumstances of the incident that allowed the backflow of the sewage water remain to be revealed. The conclusion of the technical investigations was supported by the large variety of gastrointestinal pathogens found in the stool samples, which corroborated that the contamination was due to backflow of grossly contaminated sewage water rather than, for example, surface water or sewage from only a few households. The sewage treatment plant receives sewage from a population of approximately 40,000, as well as industrial enterprises, food production establishments and a hospital.
Flushing of the area�s distribution system was initiated immediately and sustained for several weeks. As faecal indicator bacteria were still found in the drinking water after two weeks of sustained flushing, the distribution system was subsequently disinfected by chlorination on 10 and 11 February. After another two days of flushing, the drinking water was released for normal use, but recommended for drinking still only after boiling. By 12 March, the boiling restrictions were lifted for the majority of households, since by then the environmental water samples from the distribution system had fulfilled the quality criteria for untreated drinking water as defined by the Danish Ministry of Environment [3].
Commentary
The handling of the outbreak called for interdisciplinary cooperation and the epidemiological investigations supported the technical and water-microbiological analyses. Geographical information systems were used to define the contaminated area, and the 18 episodes of illness reported outside of the contaminated area (Figure 1) probably represent sporadic illness or could be associated with the outbreak in a way that was not investigated, for example by secondary transmission.
Although the drinking water supply in Denmark is primarily from untreated ground water, disease cases are rarely registered in connection with incidents of contamination [1,2]. The outbreak described was unusual, partly because of the high morbidity among the exposed citizens, and partly because of the extraordinary complexity of positive microbiological findings; a recent review of disease outbreaks caused by contaminated drinking water in the United States from 2003 to 2004 reported that in only two out of 25 outbreaks with known aetiology more than one microorganism was detected [4]. The consequences were considerable for the affected families, but also for the food companies, which were not allowed to resume production until the middle of February.

",What was the alert of the event?,"{'answer_start': [195], 'text': ['drinking water in many houses was reported to be discoloured and of unusual smell and taste.']}"
27,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","What type of samples were analyzed?
","{'answer_start': [1761], 'text': ['aecal and drinking water samples']}"
12,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

",What were the first steps of investigation?,"{'answer_start': [2040], 'text': ['trawling questionnaire']}"
29,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","What is the date of the event?
","{'answer_start': [3], 'text': ['October/November 2005']}"
18,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","What is the location of the event?
","{'answer_start': [111], 'text': ['Ireland']}"
22,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","How many people were ill?
","{'answer_start': [129], 'text': ['Eighteen']}"
19,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","How many people were hospitalized?
","{'answer_start': [313], 'text': ['Two children']}"
11,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","What are the pathogens?
","{'answer_start': [70], 'text': ['Escherichia coli (VTEC)']}"
26,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","What is the event?
","{'answer_start': [38], 'text': ['outbreak of verotoxin-producing Escherichia coli (VTEC)']}"
10,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

","What are the first steps of mitigation?
","{'answer_start': [1376], 'text': ['voluntary closure of the cr�ches']}"
33,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

",What did the authorities do to mitigate the event?,"{'answer_start': [1534], 'text': ['boil water� advisory']}"
30,Contamination Question Answering,"In October/November 2005, the largest outbreak of verotoxin-producing Escherichia coli (VTEC) ever recorded in Ireland occurred. Eighteen E. coli O157 culture-positive cases, phage type 32, verotoxin 2 positive, were identified in a small rural area of mid-west Ireland. Half of these patients were asymptomatic. Two children were admitted to hospital with haemolytic uraemic syndrome, one of whom required peritoneal dialysis, and both recovered. All 18 culture-positive patients had indistinguishable or closely related pulsed field gel electrophoresis (PFGE) patterns. Nine of the VTEC O157 culture-positive individuals were in preschool children attending two local cr�ches. Several culture-positive individuals apparently had exposure to a vulnerable private group water scheme (GWS) in an agricultural area. No microbiological evidence of VTEC was found in food or water. One veterinary sample (an animal rectal swab) was positive for E. coli O157 and the PFGE strain was indistinguishable from the outbreak strain. A case control study showed analytical epidemiological evidence of risk related to potential exposure to the GWS but not related to reported consumption of that water. Selection of cases and controls proved challenging. Transmission occurred primarily in childcare and family settings, with significant person-to-person spread. Control measures included voluntary closure of the cr�ches, exclusion of culture-positive individuals in risk groups until microbiological clearance was achieved and the issuing of a �boil water� advisory for drinking water pending upgrading of disinfection facilities.
In October 2005, the notification of a case of HUS-associated VTEC O157 led to the identification of a large outbreak in Ireland [16].
Both faecal and drinking water samples were analysed in the Biosafety Level 3 laboratory using the immunomagnetic separation method for the isolation of E. coli O157 and polymerase chain reaction for detection of VT1 and VT2 genes. Epidemiological investigations included the use of a trawling questionnaire on all culture-positive individuals. Twenty one water samples and one food sample were tested specifically for E. coli O157. Rainfall data supplied by Met �ireann (the Irish Meteorological Service) at a nearby station for the period around the outbreak was collated. A questionnaire was compiled and piloted. Two cases were hospitalised. A �boil water� advisory was issued to users of the GWS pending upgrading of disinfection facilities. A point source was initially suspected, possibly from environmental contamination of vulnerable drinking water, but this was not proven. Subsequent to the outbreak, an education initiative advising childcare facilities about VTEC was launched in 2006

",What were the associated pathogens of concern?,"{'answer_start': [1908], 'text': ['E. coli O157']}"
28,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
",What symptoms did the people had?,"{'answer_start': [2280], 'text': ['diarrhoea']}"
34,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
",What caused the event?,"{'answer_start': [14082], 'text': ['firefighting']}"
7,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
",What symptoms did people report?,"{'answer_start': [7763], 'text': ['Diarrhoea']}"
20,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What is the initial cause of the event?
","{'answer_start': [13181], 'text': ['incident during the firefighting']}"
12,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What is the date of the event?
","{'answer_start': [135], 'text': ['6 December 2010']}"
12,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What is the location of the event?
","{'answer_start': [216], 'text': ['Belgium']}"
20,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
",What pathogen was connected to the outbreak?,"{'answer_start': [12032], 'text': ['Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples']}"
22,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","How was the event first detected?
","{'answer_start': [576], 'text': ['routinely taken tap water samples']}"
16,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","How many people were ill?
","{'answer_start': [6618], 'text': ['603 patients']}"
17,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","How many people were hospitalized?
","{'answer_start': [6886], 'text': ['Six patients']}"
32,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What is the attack rate?
","{'answer_start': [14170], 'text': ['18.7%']}"
20,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","How many people died?
","{'answer_start': [6918], 'text': ['One patient']}"
25,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What are the pathogens?
","{'answer_start': [0], 'text': ['Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia']}"
6,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [12602], 'text': ['>200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. ']}"
18,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What are the symptoms?
","{'answer_start': [2000], 'text': ['gastroenteritis']}"
22,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What is the event?
","{'answer_start': [225], 'text': ['Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water']}"
28,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What are the initial steps of investigation?
","{'answer_start': [1317], 'text': ['We conducted an epidemiological study to describe the size and identify the source of the outbreak.']}"
22,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What are the first steps of mitigation?
","{'answer_start': [805], 'text': ['advised not to consume or use tap water']}"
14,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What did the local authorities advise?
","{'answer_start': [12985], 'text': ['Bottled potable water was distributed to the population']}"
24,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What type of samples were examined?
","{'answer_start': [116], 'text': [' stool samples']}"
15,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What steps were taken to restore the problem?
","{'answer_start': [13042], 'text': ['Sanitation of water pipes']}"
19,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What measures were taken to prevent the event?
","{'answer_start': [13533], 'text': ['a warning was sent to other re brigades ']}"
28,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
","What was the age of the affected people?
","{'answer_start': [6672], 'text': ['The age ranged from 1 to 91 years with a median age of 36 years']}"
31,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
",What is the source of contamination?,"{'answer_start': [13707], 'text': ['consumption of water contaminated by river water']}"
20,Contamination Question Answering,"Campylobacter sp. (2/56), norovirus GI and GII (11/56), rotavirus (1/56) and Giardia lamblia (3/56) were detected in stool samples. On 6 December 2010 there was a fire in a textile factory in the centre of Hemiksem, Belgium. Fireghters used water from two hydrants, connected to the tap water network, and from a unit hydrosub, which is used for pumping surface and river water. Car pumps collected water from both sources in a pressurized water tank. The hydrosub was connected to the river Vliet, a small river that ows to the river Scheldt. On 7 December three out of four routinely taken tap water samples in Hemiksem and Schelle suggested fecal contamination. Local general practitioners (GPs) reported an increase in consultations for gastroenteritis on 8 December. On 9 December the residents were advised not to consume or use tap water. The water avoidance notice was lifted on 20 December 2010. Tap water in the neighbouring municipalities of Hemiksem and Schelle (n=18620 residents), is supplied by one water supply company that uses purified ground water. The company takes care of collecting, cleaning and distributing drinking water. The surveillance, done according to the specic legislation, is a responsibility of the water company. Belgium has no specic surveillance system on waterborne outbreaks. We conducted an epidemiological study to describe the size and identify the source of the outbreak. METHODS The study population comprised of all the residents of Hemiksem and Schelle. We included no other municipalities given that elsewhere no faecal contamination in routinely taken samples of drinking water had been reported, and no increase of gastroenteritis had been registered. Considering that symptoms of gastroenteritis can be very mild, we combined a physicians case-finding survey with a randomly sampled survey among the subscribers of the water company in Hemiksem and Schelle. Case reporting by physicians On 9 December all 18 local GPs were asked to report cases of gastroenteritis. Additionally, the emergency department of a neighbouring hospital was contacted and asked to report any resident of Hemiksem or Schelle who presented with gastroenteritis. Inclusion criteria were patients who lived in Hemiksem or Schelle, and who had symptoms of diarrhoea (53 loose stools per 24 h) or vomiting from 6 to 13 December 2010. Retrospective cohort study A retrospective cohort study was conducted among a randomly selected sample of 1000 households from Hemiksem and Schelle. The sample was selected from a list of customers of the water supply company. A household was identifed as all persons living at the same address. Through a postal survey every house- hold member was asked for his personal usage of tap water (consumption, cooking, teeth brushing, cleaning), the usage of other water (ground water, bottled water), symptoms, with a focus on gastrointestinal symptoms, and the onset date of these symptoms and treatments. Any person reporting diarrhoea (53 loose stools per 24 h) and/or vomiting between 6 and 13 December 2010, was identifed as a case. Patients with an onset of diarrhoea or vomiting between 14 and 31 December 2010 were considered as late or secondary cases. Non-cases were people who did not re- port any symptoms. Households in which symptoms of gastroenteritis were reported prior to 6 December 2010 and persons who spent time abroad in the week prior to the outbreak were excluded from the study. We did not correct for a baseline number of gastroenteritis cases as no adequate incidence data for gastroenteritis was present for this region and time period. Based on the address of the respondent, 712 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at the shortest distance, in metres, to the site of the re was calculated. Descriptive statistics were calculated for the retrospective cohort study. We performed univariate analysis (cross tables, 2 tests, linear trend analysis, relative risk) and multivariate analysis (Poisson regression). P<005 was considered statistically significant. Variables associated with the outcome at P<020 in uni- variate analysis were introduced in the multivariate regression model. The nal multivariate model was built using backwards elimination [22]. The data were entered using EpiData v. 3.1 (EpiData Associ- ation, Denmark) and analysed using SAS v. 9.2 (SAS Institute Inc., USA) and R 2.14 (R Foundation, Austria). An additional analysis focusing on the geo- graphical distribution of the cases was performed using the R package sparr [23]. With this software the spatial density of the cases and the spatial density of non-cases was compared. Microbiological study Patients included in the physicians survey were con- tacted and asked to provide a stool sample. These stool samples were tested for pathogenic gastrointestinal bacteria on culture media for isolation of entero- pathogens (MacConkey agar, XLD and CIN agar) in a laboratory with accreditation to ISO 15189. Antigen tests were used to test for Cryptosporidium and G. lamblia (Xpect Immunochromatographic Assays, Oxoid, UK). For the detection of NoV two methods were used. Three stool samples were send to the Scientic Institute of Public Health, Brussels, where they used a real-time RTPCR for the detection and differentiation of the two most important human genogroups of NoV, GI and GII. This method is de- scribed in ISO/TS 152161: 2013. The other 53 stool samples were send to the Clinical Virology Labora- tory, Leuven and were analysed with a NoV RT PCR. Two pairs of specic primers G1SKF/G1SKR and COG2F/G2SKR, that amplify the capsid gene, were used to respectively detect NoV GI (330 bp) and NoV GII (387 bp) [24]. An in-house RTPCR was developed for detection of astrovirus. The primer set used to amplify 272 bp in the capsid protein gene was HASTV-F: ACAGAAGAGCAACTCCATCGC and HASTV-R: TGACACCYTGTTTCCTGAGTTG. A RTPCR was used for rotavirus and adenovirus de- tection as described previously [25, 26]. The analyses of the tap water were performed by the water supply company. Samples were tested for bacterial indicators of faecal contamination: non-specic coliforms, Escherichia coli, Clostridium sp. and Pseudomonas aeruginosa. In two river water samples protozoa were isolated by the department of Parasitology of the University of Ghent. RESULTS Physicians case-finding study All 18 GPs participated in the study. We included 603 patients; 326 (54%) were men and 277 (46%) women. The age ranged from 1 to 91 years with a median age of 36 years. Three hundred and ninety-seven (66%) cases lived in Hemiksem, and 206 (34%) in Schelle. Consultations for gastroenteritis peaked on 8 December 2010. Six patients were hospitalized. One patient, aged 91 years, died due to intestinal bleeding on 12 December after being admitted to the hospital for gastroenteritis on 9 December 2010. Retrospective cohort study The questionnaire was distributed on 20 December. The response rate was 528% (n=528). The responses included information on a total of 1185 household members. This is 66% of the total population (n=18620) of Hemiksem and Schelle (December 2010). The respondents age ranged from 0 to 99 years and the median age was 39 years. Gender was balanced with 481% males and 519% females. Out of all respondents, 37% regularly drank tap water, with an average of 37 glasses a day, 99% used tap water to brush their teeth, and 98% used tap water to wash vegetables and fruit. Gastrointestinal symptoms were reported by 365% (n=432). The mean duration of ill- ness was 41 days. Diarrhoea was the most frequently reported symptom, present in 654% of those reporting symptoms, fever in 15%, vomiting in 39% and nausea in 60%. Thirty-four respondents reported symptoms prior to 6 December. A total of 222 [187%, 95% condence interval (CI) 164209] persons met the case definition (onset of symptoms 613 December) and 176 were late or secondary cases (onset after 13 December). The incidence of gastroenteritis followed a steep incline from 6 to 8 December and peaked on 8 December (Fig. 1). The density of the cases (n=222) over non-cases (n=753) shows the highest proportion of cases slightly Waterborne outbreak, Hemiksem, 2010 713 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at north of the site of the re (Fig. 2). The density of self- reported tap-water drinkers is compared to the den- sity of non-tap-water drinkers (see Fig. 3). A higher proportion of tap-water drinkers was observed east of Hemiksem. Univariate analysis Drinking tap water was associated with gastrointestinal symptoms [relative risk (RR) 228, 95% CI 194 267] (Table 1). The relative risk was higher for cases 80 70 60 50 40 30 20 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 December 2010 Stop consumption of tap water Fire 20 21 26 28 New cases Pre-load Early eases Late/secondary cases Fig. 1. Cases over time, subscribers study, Hemiksem and Schelle, 2010. Fig. 2. Density cases over non-cases. A redder region indicates a higher proportion of cases over non-cases; dotted line=contour line for signicance P<005; full line=contour line for signicance P<001; Hemiksem and Schelle, 2010. 714 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at (RR 367, 95% CI 286470) than for secondary or late cases (RR 191, 95% CI 147249) (Table 1). The distance from the home address of the respondent to the site of the re was signicantly shorter for cases com- pared to non-cases. Other variables such as gender, household size, age and the presence of young children (<12 years) in the family were not signicant (Table 2). Multivariate analysis The independent variables included in the multivari- ate model were: glasses of tap water a day, location and gender. Location (distance from the site of the re) as well as drinking tap water (glasses per day) were signicantly (P<005) associated with outcome in a Poisson regression model. For each glass of tap water consumed the risk was augmented by 21% (RR 121, 95% CI 116126). For each 250 m that families lived further away from the site of the re the risk dimin- ished by 84% (RR 092, 95% CI 084099) (Table 3). Microbiological patient data Sixteen of 56 stool samples were diagnosed with a pathogen. In the stool sample of 14 patients a single Table 1. Contingency table for drinking tap water and the different case denitions (for 46 respondents information on tap water consumption was missing), Hemiskem and Schelle, 2010 Non-cases Secondary and late cases Cases Total Tapwater No N 549 95 74 718 % 7369 5523 3303 Yes N 196 77 148 421 % 2631 4477 6697 Total N 745 172 222 1139 Table 2. Univariate analysis of risk factors in cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water 367 286470 0001 Gender (male/female) 08 0611 008 Distance to re site (unit: 750 m) 089 082097 004 Young children (<12 years) 09 0712 06 Household size Linear trend  043 Age Linear trend  052 RR, Relative risk; CI, condence interval. Fig. 3. Density of tap-water drinkers over non-tap-water drinkers. A redder region indicates a higher proportion of tap-water drinkers; Hemiksen and Schelle, 2010. Waterborne outbreak, Hemiksem, 2010 715 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at pathogen was detected: Campylobacter sp. was detected in one, NoV GI in two and NoV GII in seven patients. Rotavirus was detected in one patient and G. lamblia was detected in three samples. Two patients were diagnosed with a multi-pathogen infec- tion: one patient with a double infection: NoV GI and GII, and one patient with a mixed infection with Campylobacter jejuni, NoV GI and GII. Environmental study Between 8 and 25 December 2010, 625 water samples were analysed in Hemiksem and Schelle. In Hemiksem, high densities of faecal pollution indicators were detected in tap water samples: >200 c.f.u./100 ml for E. coli and >1100 c.f.u./100 ml for enterococci. Parasites, G. lamblia and Cryptospori- dium sp. were isolated from samples taken from the river. Control measures There were different authorities involved in control- ling the outbreak and informing the population; the local municipal authorities, the environmental health team and the drinking water company. Bottled potable water was distributed to the population. Sanitation of water pipes (flushing, disinfection) was performed from 9 December 2010 to 25 December 2010. Our research pointed towards an incident during the firefighting on 6 December 2010 as the cause of the contamination. Additional research eliminated other possible reasons by checking installations in the surrounding area. An investigation into the actions taken by firefighters pointed towards the absence of reflux valves as the most likely cause. Once this hazard was identified, a warning was sent to other re brigades in Belgium to avoid similar incidents. DISCUSSION We have described a large community outbreak of gastroenteritis associated with the consumption of water contaminated by river water during fire extinguishing. This is the rst large waterborne outbreak described in Belgium. Waterborne disease, especially cryptosporidiosis, has been reported as a work- related disease exposure for firefighters, but it is the first time a community outbreak has been described in which the probable cause was associated with firefighting [27]. Our study estimated an attack rate of gastrointestinal infections of 18.7% without correction for baseline illness. The attack rate in our study can be explained by the high doses of pathogens in the tap water, a high daily consumption of tap water, a period of 3 days between the contamination and the water avoidance notice, and the low infectious dose of some pathogens. Attack rates in comparable studies vary and can be quite high, e.g. 514% in a tourist resort and new housing estate, 53% in a Finnish town [15, 20, 21, 28]. The number of cases per outbreak has been associated to the pathogens involved. Giardia- and Cryptosporidium-associated outbreaks have the lowest mean number of cases per outbreak (116 and 177, respectively). Viral outbreaks and out- breaks associated with Campylobacter sp. have the highest mean number of cases per outbreak (1545 and 1802, respectively) [1]. In a multi-pathogen out- break, as we have described, one can expect an even higher number of cases. The number of hospitalizations was limited, but gastrointestinal disease can be associated with severe illness, especially in hig- risk patients [6] such as AIDS patients [29]. We found an unadjusted relative risk of 367 and the doseresponse relationship was signicant. A threefold increased risk for illness with the con- sumption of tap water is commonly associated with waterborne outbreaks [13, 16, 18, 19]. In E. coli and Campylobacter sp. outbreaks with relative risks of 11 were reported [7, 9]. In waterborne outbreaks, the strength of evidence implicating water as the cause of an outbreak is deter- mined on the basis of ndings from epidemiological and microbiological investigations. Tillett et al. devel- oped a system of levels of evidence to link an outbreak to water [30]. We complement this by adding an important spatial component. We observed a steep increase in reported gastroen- teritis among the surveys responders on the 6 Table 3. Multivariate analysis (Poisson regression) for cases compared to non-cases, Hemiksem and Schelle, 2010 Variable RR 95% CI P value Tap water (glasses/day) 121 116127 <0001 Distance to re site (unit: 250 m) 092 084099 <004 RR, Relative risk; CI, condence interval. 716 T. Braeye and others https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0950268814001629 Downloaded from https://www.cambridge.org/core. IP address: 82.217.87.172, on 14 Oct 2021 at 12:20:23, subject to the Cambridge Core terms of use, available at December which indicates a sudden contamination. Microbiological investigations during this increase identified multiple pathogens in the stool samples of patients. This is consistent with the hypothesis of a waterborne outbreak rather than a community-wide person-to-person transmission of e.g. a NoV [31]. Furthermore, tap water was a likely mode of trans- mission as there was a significant association between gastroenteritis and the consumption of tap water. Enterobacteriaceae were found in the tap water. We linked the firefighting to the outbreak by spatial and temporal analysis. We documented the association be- tween place of residence and the risk of gastroenteritis by comparing the ratio of cases (n=222) over non-cases (n=753) with the ratio of tap-water drinkers over non-tap-water drinkers. We observed that one peak in the ratio of cases over controls was not accompanied bya high ratio of tap-water drinkers over non-tap-water drinkers. This cluster was located slightly north of the site of the re. We have no data on quantitative difference of pathogen load in the pipelines. A major weakness of this study is the incomplete microbiological investigation. Drinking watercontami- nated by sewage is known to result in mixed bacterial and viral infections and severe acute gastroenteritis regardless of the aetiological agents [17, 32]. Investigation of the tap water was limited to indicator bacteria for faecal contamination and a one-time detection of Cryptosporidium sp. and G. lamblia. Patients were not tested for protozoa. Detection of e.g. levels of serum antibody to G. lamblia or testing of patients for Cryptosporidium should be performed in this kind of outbreak investigation [33, 34]. No attempt was made to match the clinical and environmental pathogens. Pathogens from the environmental samples were not stored and therefore not available for further testing. Since the incubation period of several gastrointestinal pathogens can vary from hours to weeks, we took the entire month of December 2010 as study period. However, the difference between cases and late or secondary cases is artificial and only used as a means to better analyse the data. Long incubation periods and secondary infections by person-to-person transmission are hard to differentiate. Self-reported information on symptoms and water consumption is known to be biased, especially after media attention [35]. However, the media did not report on possible sources and the connection to the fire. The media only started to report on the outbreak after the water avoidance notice. We tried to collect objective information by contacting healthcare personnel. The questionnaire was sent rather late, on 20 December 2010, which could generate recall bias. Moreover, persons affected by the outbreak might be more inclined to respond to the survey leading to selection bias. No information was collected on the costs of this outbreak. Previous research shows that the costs for preventive measures clearly are smaller than the costs of a waterborne outbreak [36]. We did not investigate compliance with the water avoidance notice. A study in The Netherlands estimated compliance with a boil water advice at 818% [37]. Several improvements can be recommended such as the development of a surveillance system and a wider and more thorough microbiological investigation. Syndromic surveillance combined with water incident and consumer complaints data can be used for the timely detection of outbreaks, but this needs to be further evaluated [38]. More intense microbiological investigations are necessary both during standard controls and outbreaks. Previous studies have indicated that water-treatment technologies have become inad- equate, and that a negative coliform test result does not guarantee that water is free from all pathogens, especially from protozoan agents [6]. Both enteric viruses, such as caliciviruses, and some protozoan agents, such as Cryptosporidium, are candidates for endemic transmission and outbreaks with these pathogens will go undetected with standard controls [39]. Furthermore, a more thorough microbiological investigation can be used to predict the likelihood of various transmission routes or vehicles [40]. This outbreak also highlights the need to rapidly connect an outbreak to its cause to reduce attack rates by implementing the correct measurements. This outbreak could have been detected quicker if additional surveillance systems had been in place. Rapid detection and intervention necessitates the collaboration between physicians, public health services, microbiologists and water providers. 
",What was the alert of the event?,"{'answer_start': [664], 'text': [' Local general practitioners (GPs) reported an increase in consultations for gastroenteritis']}"
25,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
",What symptoms did the people had?,"{'answer_start': [2584], 'text': ['diarrhoea (o3 loose stools/day) or vomiting']}"
34,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
",What symptoms were developed?,"{'answer_start': [3758], 'text': ['diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain']}"
28,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What type of samples were analyzed?
","{'answer_start': [3615], 'text': ['Stool specimens']}"
21,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the initial cause of the event?
","{'answer_start': [1909], 'text': ['A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. ']}"
11,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the date of the event?
","{'answer_start': [1452], 'text': ['30 November']}"
18,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the location of the event?
","{'answer_start': [106], 'text': ['Finnish town']}"
30,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
",What pathogen was connected to the outbreak?,"{'answer_start': [4073], 'text': ['norovirus']}"
28,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the source that started the event?
","{'answer_start': [4422], 'text': ['Drinking-water contamination']}"
13,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","How was the event first detected?
","{'answer_start': [1207], 'text': ['customers complained of a bad smell and taste in their tap water.']}"
8,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","How many people were ill?
","{'answer_start': [709], 'text': ['8453 residents']}"
17,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the attack rate?
","{'answer_start': [815], 'text': ['53%']}"
28,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What are the pathogens?
","{'answer_start': [2206], 'text': ['adenoviruses and noroviruses ']}"
17,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What are the symptoms?
","{'answer_start': [1550], 'text': ['diarrhoea and vomiting']}"
29,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the event?
","{'answer_start': [0], 'text': ['An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water']}"
30,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What is the duration of the event?
","{'answer_start': [2501], 'text': ['almost 3 months']}"
8,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What are the first steps of mitigation?
","{'answer_start': [1709], 'text': ['Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. ']}"
5,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
","What measures were taken to prevent the event?
","{'answer_start': [4324], 'text': ['waterworks across the country ']}"
17,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
",What is the source of contamination?,"{'answer_start': [2115], 'text': ['drinking-water network became contaminated with sewage effluent']}"
11,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
",What was the alert of the event?,"{'answer_start': [1511], 'text': ['officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre.']}"
18,Contamination Question Answering,"An inappropriate cross-connection between sewage and drinking-water pipelines contaminated tap water in a Finnish town, resulting in an extensive waterborne gastroenteritis outbreak in this developed country. According to a database and a line-list, altogether 1222 subjects sought medical care as a result of this exposure. Seven pathogens were found in patient samples of those who sought treatment. To establish the true disease burden from this exposure, we undertook a population-based questionnaire investigation with a control population, infrequently used to study waterborne outbreaks. The study covered three areas, contaminated and uncontaminated parts of the town and a control town. An estimated 8453 residents fell ill during the outbreak, the excess number of illnesses being 6501. Attack rates were 53% [95% confidence interval (CI) 49.556.4] in the contaminated area, 15.6% (95% CI 13.118.5) in the uncontaminated area and 6.5% (95% CI 4.88.8) in the control population. On Wednesday, 28 November 2007, maintenance work was conducted at the waste water plant in Nokia. The same day, technical problems were encountered in the municipal drinking-water system, and during the days following, customers complained of a bad smell and taste in their tap water. These were first misinterpreted as being caused by harmless deposits loosened from the inner walls of the pipeline and discharged during the maintenance work on 28 November. From 30 November, environmental health and municipal waterworks officials received reports of bouts of diarrhoea and vomiting among residents, and during that same day an increase in the number of patients with gastroenteritis was observed at the health centre. Extensive water and pipeline sampling was initiated and a boil-water notice issued, and water chlorine concentration was increased. The water contamination and its source became evident the same day. A valve in the waste-water plant connecting the drinking-water line and a waste-water effluent line had been opened during the maintenance work and inadvertently left open for 2 days. As a consequence, the drinking-water network became contaminated with sewage effluent. In the contaminated area, adenoviruses and noroviruses were repeatedly detected in water-supply samples despite chlorination and pipeline flushing. Finally, after extensive decontamination procedures including shock chlorination, precautionary restrictions were discontinued in the contaminated area on 18 February 2008, almost 3 months after the incident. A case was defined as a person suffering acute diarrhoea (o3 loose stools/day) or vomiting between 28 November 2007 and 20 January 2008. The occurrence of gastroenteritis during a 10-month period prior to the outbreak was also enquired about to ensure the comparability of the study groups. Faecal specimens for bacterial pathogens were not investigated from all the patients or from representative samples from consecutive cases. Instead, bacterial samples were available from cases with more severe symptoms. Specimens for detection of norovirus were collected from five randomly selected patients within the first week of the outbreak. Other viral pathogens were studied in samples from children admitted to the emergency department of the University Hospital. In order to detect enteric parasites specimens were taken from ten consecutive patients during the second week of the outbreak. Subsequently, when cases with giardiasis were detected, parasites were investigated in all symptomatic patients. Specimens were taken at the health centre or in the University Hospital. Stool specimens were cultured for the presence of Campylobacter, Salmonella, Yersinia and Shigella spp. The most common symptoms reported were diarrhoea (n=813, 79%), vomiting (n=601, 59%), fever (n=337, 33%) and abdominal pain (n=291, 28%). Enteropathogens were detected in faecal specimens (Table 3). The most frequently encountered was Campylobacter sp., with C. jejuni representing most of them, followed by Giardia. Five random samples investigated for norovirus were collected on 2 December 2007 and all were positive. Other findings included non-typhoidal salmonellas, Clostridium difficile and rotavirus. Four stool cultures grew Shigella boydii. After the outbreak, the national authorities required waterworks across the country to rule out the presence of similar cross-connection constructions. Drinking-water contamination was considered to be the obvious source of this outbreak, and this study provides strong evidence to support the assumption.
",What were the associated pathogens of concern?,"{'answer_start': [4164], 'text': ['non-typhoidal salmonellas, Clostridium difficile and rotavirus']}"
5,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What type of samples were analyzed?
","{'answer_start': [724], 'text': ['stool samples']}"
14,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
",What caused the event?,"{'answer_start': [3458], 'text': ['drinking water contamination caused by congestion of the combined rainwater drainage and sewage system']}"
5,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
",What did the local authorities investigate?,"{'answer_start': [1603], 'text': ['online questionnaire']}"
8,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What is the initial cause of the event?
","{'answer_start': [3129], 'text': ['backflow of sewage water into the gravel surrounding the borehole']}"
20,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What is the date of the event?
","{'answer_start': [41], 'text': ['June 2009']}"
13,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What is the location of the event?
","{'answer_start': [131], 'text': ['Danish town']}"
16,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
",What pathogen was connected to the outbreak?,"{'answer_start': [880], 'text': ['coliform bacteria']}"
19,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","How was the event first detected?
","{'answer_start': [1129], 'text': ['unusual increase in patients with acute gastroenteritis.']}"
23,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","How many people were ill?
","{'answer_start': [492], 'text': ['163 cases']}"
20,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What is the attack rate?
","{'answer_start': [526], 'text': ['16%']}"
29,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What are the pathogens?
","{'answer_start': [650], 'text': ['Campylobacter jejuni']}"
29,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What are the symptoms?
","{'answer_start': [1916], 'text': ['diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting']}"
20,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What is the event?
","{'answer_start': [144], 'text': ['The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. ']}"
28,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What are the first steps of mitigation?
","{'answer_start': [1362], 'text': ['tap-water boiling advice']}"
12,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What type of samples were examined?
","{'answer_start': [848], 'text': ['Water samples']}"
25,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
",What did the authorities do to mitigate the event?,"{'answer_start': [2897], 'text': ['boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks']}"
24,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
","What was the age of the affected people?
","{'answer_start': [2447], 'text': ['mean age 42 years)']}"
29,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
",What is the source of contamination?,"{'answer_start': [3310], 'text': ['drinking water']}"
26,Contamination Question Answering,"Following an unusually heavy rainfall in June 2009, a community-wide outbreak of Campylobacter gastroenteritis occurred in a small Danish town. The outbreak investigation consisted of (1) a cohort study using an e-questionnaire of disease determinants, (2) microbiological study of stool samples, (3) serological study of blood samples from cases and asymptomatic members of case households, and (4) environmental analyses of the water distribution system. The questionnaire study identified 163 cases (respondent attack rate 16%). Results showed a significant dose-response relationship between consumption of tap water and risk of gastroenteritis. Campylobacter jejuni belonging to two related aA types were isolated from stool samples. Serum antibody levels against Campylobacter were significantly higher in cases than in asymptomatic persons. Water samples were positive for coliform bacteria, and the likely mode of contamination was found to be surface water leaking into the drinking-water system. In the week beginning 15 June 2009, general practitioners (GPs) in the town of Tune, 30 km south of Copenhagen, noticed an unusual increase in patients with acute gastroenteritis. Campylobacter spp. were detected in stool cultures from some patients. The suspicion of a waterborne gastroenteritis outbreak was raised, an outbreak investigation began and a tap-water boiling advice was issued on 20 June. In the following, we present the outbreak analysis, including a serological follow-up study of persons affected by this waterborne Campylobacter outbreak. A cohort study was initiated using an online questionnaire with questions about signs and symptoms, onset date, duration of illness and exposure to potential sources of Campylobacter infection (e.g. consumption of unboiled tap water, poultry or raw milk, eating ready-to-eat meals from local shops, etc.). A clinical case was defined as a person with diarrhoea (>3 loose stools in 24 h) or abdominal pain with either fever or vomiting, with symptom onset during the period 13-26 June 2009. A confirmed case was defined as a clinical case with a stool culture positive for Campylobacter spp. Water samples were repeatedly taken at the waterworks and at multiple points of the water pipe network following the suspected contamination event. The questionnaire survey was completed by a total of 1039 individuals, response rate 21%, (61% females, 39% males) ranging from 1 to 86 years (mean age 42 years). Of the remaining 933 persons, 159 (153%) were classified as cases and 774 as non-cases, based on their reported symptoms and onset dates. Of these, 41 were culture-positive for Campylobacter jejuni. Cultures for other enteric bacteria were negative. Virological investigations detected sapovirus in two (10%) out of 20 samples tested, and one patient tested positive for both sapovirus and C. jejuni. During 20 June to 30 July, a boiling order was in place for the whole town and the inhabitants were supplied with drinking water from tank trucks. The technical assessment revealed a faulty installation adjacent to one of the boreholes which may have allowed a backflow of sewage water into the gravel surrounding the borehole, when the sewage system was congested due to the heavy rainfall on 12 June. The outbreak was most likely caused by drinking water as shown by several lines of evidence. Second, an exceptionally heavy rainfall occurred a few days before the outbreak, leading to a drinking water contamination caused by congestion of the combined rainwater drainage and sewage system. ailable at 
",What were the associated pathogens of concern?,"{'answer_start': [1186], 'text': ['Campylobacter spp']}"
32,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
",What symptoms did the people had?,"{'answer_start': [1115], 'text': ['abdominal pain, nausea and headache']}"
27,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What type of samples were analyzed?
","{'answer_start': [724], 'text': ['water samples']}"
22,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
",What symptoms did people report?,"{'answer_start': [647], 'text': ['omiting, nausea, abdominal pain, fever']}"
26,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What is the date of the event?
","{'answer_start': [6], 'text': ['March 2012']}"
21,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What is the location of the event?
","{'answer_start': [158], 'text': ['Norwegian']}"
11,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
",What pathogen was connected to the outbreak?,"{'answer_start': [1425], 'text': ['Cryptosporidium oocysts ']}"
13,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What is the source that started the event?
","{'answer_start': [2496], 'text': ['oocysts in the faeces of infected lambs and/or goat kids']}"
21,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","How was the event first detected?
","{'answer_start': [18], 'text': ['the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis']}"
19,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","How many people were ill?
","{'answer_start': [1775], 'text': ['40']}"
25,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What is the attack rate?
","{'answer_start': [1843], 'text': ['19%']}"
28,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What are the pathogens?
","{'answer_start': [182], 'text': ['Cryptosporidium oocysts ']}"
20,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What is the concentration of the contaminant after analysis?
","{'answer_start': [2311], 'text': ['>1*10^6 oocysts/g faeces']}"
29,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What are the symptoms?
","{'answer_start': [565], 'text': ['diarrhoea']}"
27,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What is the event?
","{'answer_start': [85], 'text': ['several cases of gastroenteritis']}"
23,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What are the initial steps of investigation?
","{'answer_start': [267], 'text': ['A retrospective cohort study was conducted']}"
5,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","From when until when the event happened
","{'answer_start': [939], 'text': ['The first case reported symptoms on the evening of 5 March and the last on 18 April']}"
28,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What type of samples were examined?
","{'answer_start': [225], 'text': ['faecal samples ']}"
20,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
","What was the age of the affected people?
","{'answer_start': [1867], 'text': ['between 10-14 years']}"
23,Contamination Question Answering,"On 25 March 2012, the Norwegian Institute of Public Health (NIPH) was notified about several cases of gastroenteritis in schoolchildren following a stay at a Norwegian holiday farm. Cryptosporidium oocysts were identified in faecal samples from some of the children. A retrospective cohort study was conducted in school- children, teachers and farm staff who had been on the holiday farm during the period 5-23 March 2012. For the analytical study, the case definition was restricted to a person who had been on the farm in the relevant period, and had experienced diarrhoea or at least two of the following symptoms within 2 weeks of the visit: vomiting, nausea, abdominal pain, fever, with duration of illness >1 day. The water samples were analysed using the NVH internal method for Cryptosporidium oocysts and Giardia cysts. Of the 209 respondents, 78 reported gastrointestinal illness following the visit (75 children, three adults). The first case reported symptoms on the evening of 5 March and the last on 18 April. Illness onset of the farm staff was between 15 and 21 March. The most common symptoms were abdominal pain, nausea and headache (Table 1). Median duration of symptoms was 45 days, ranging from a few hours to >2 weeks. Most cases included in the analytical study (43%, 17/40) reported symptoms 79 days after arrival at the farm (Fig. 1). Of the pupils answering the questionnaire and reporting illness, Cryptosporidium oocysts were detected in faecal samples from eight cases. Most laboratory-diagnosed cases (100%, 8/8) expressed abdominal pain, diarrhoea (7/8), fever (7/8), nausea (6/8) and headache (5/8). Half of the cases reported vomiting (50%, 4/8) (Table 1). Only three of the cases reported contact with ill persons before symptom onset. Only 40 matched the case definition of the analytical study (attack rate 19%), and all were aged between 10-14 years. Nine faecal samples received early in the investigation were analysed for Salmonella, Shigella, Yersinia, Campylobacter, norovirus, sapovirus, Giardia cysts and Cryptosporidium oocysts; all were positive for Cryptosporidium and negative for other enteropathogens. Most of these samples contained low oocyst concentrations, but the faecal sample from one lamb contained a very high concentration of Cryptosporidium oocysts (>1*10^6 oocysts/g faeces). This investigation indicates that the outbreak was probably due to direct or indirect contact with infected animals. The source of this outbreak was probably oocysts in the faeces of infected lambs and/or goat kids. 
",What is the source of contamination?,"{'answer_start': [2405], 'text': ['direct or indirect contact with infected animals']}"
8,Contamination Question Answering,"Seven people, some of them children, have been diagnosed with E.coli 0157 in a single village.
A further eight people who share the same private water supply are also being tested for the infection.
The water is shared by eight homes in Auchinclech, near Westhill in Aberdeenshire.
Two of the affected people were treated at Aberdeen Royal Infirmary and have now been discharged. The remainder were seen by their GPs.
Health officials at NHS Grampian said the infection was not affecting public water supplies.
A spokesman said: ""None of those affected are currently giving cause for concern.""
Householders in the affected homes are being advised to boil their water while the inquiry to identify the source of the infection continues.
Dr Helen Howie, a consultant in public health medicine at NHS Grampian, said: ""A letter went out to all residents last night to let them know what is going on.""
She added that investigators were examining whether heavy rainfall in the area in recent weeks could have led to the outbreak.
Dr Howie said: ""This outbreak highlights the risks associated with private water supplies.
""Such supplies are liable to bacteriological contamination causing infections such as E.coli O157.
""Householders are encouraged to contact the Environmental Health Service and seek advice on how to improve their supply.""
E.coli O157 is most commonly found in the intestines of cattle.
Humans can become infected by contaminated water or foods, inadequately cooked meat and dairy products, direct contact with animals and by person-to-person spread.
Symptoms include nausea, vomiting and diarrhoea.
In 1996 the O157 strain of the bug killed 21 elderly people in Wishaw, Lanarkshire, during the world's worst recorded instance of E.coli poisoning.


","What is the location of the event?
","{'answer_start': [267], 'text': ['Aberdeenshire']}"
7,Contamination Question Answering,"Seven people, some of them children, have been diagnosed with E.coli 0157 in a single village.
A further eight people who share the same private water supply are also being tested for the infection.
The water is shared by eight homes in Auchinclech, near Westhill in Aberdeenshire.
Two of the affected people were treated at Aberdeen Royal Infirmary and have now been discharged. The remainder were seen by their GPs.
Health officials at NHS Grampian said the infection was not affecting public water supplies.
A spokesman said: ""None of those affected are currently giving cause for concern.""
Householders in the affected homes are being advised to boil their water while the inquiry to identify the source of the infection continues.
Dr Helen Howie, a consultant in public health medicine at NHS Grampian, said: ""A letter went out to all residents last night to let them know what is going on.""
She added that investigators were examining whether heavy rainfall in the area in recent weeks could have led to the outbreak.
Dr Howie said: ""This outbreak highlights the risks associated with private water supplies.
""Such supplies are liable to bacteriological contamination causing infections such as E.coli O157.
""Householders are encouraged to contact the Environmental Health Service and seek advice on how to improve their supply.""
E.coli O157 is most commonly found in the intestines of cattle.
Humans can become infected by contaminated water or foods, inadequately cooked meat and dairy products, direct contact with animals and by person-to-person spread.
Symptoms include nausea, vomiting and diarrhoea.
In 1996 the O157 strain of the bug killed 21 elderly people in Wishaw, Lanarkshire, during the world's worst recorded instance of E.coli poisoning.


",What pathogen was connected to the outbreak?,"{'answer_start': [1201], 'text': ['E.coli O157']}"
22,Contamination Question Answering,"Seven people, some of them children, have been diagnosed with E.coli 0157 in a single village.
A further eight people who share the same private water supply are also being tested for the infection.
The water is shared by eight homes in Auchinclech, near Westhill in Aberdeenshire.
Two of the affected people were treated at Aberdeen Royal Infirmary and have now been discharged. The remainder were seen by their GPs.
Health officials at NHS Grampian said the infection was not affecting public water supplies.
A spokesman said: ""None of those affected are currently giving cause for concern.""
Householders in the affected homes are being advised to boil their water while the inquiry to identify the source of the infection continues.
Dr Helen Howie, a consultant in public health medicine at NHS Grampian, said: ""A letter went out to all residents last night to let them know what is going on.""
She added that investigators were examining whether heavy rainfall in the area in recent weeks could have led to the outbreak.
Dr Howie said: ""This outbreak highlights the risks associated with private water supplies.
""Such supplies are liable to bacteriological contamination causing infections such as E.coli O157.
""Householders are encouraged to contact the Environmental Health Service and seek advice on how to improve their supply.""
E.coli O157 is most commonly found in the intestines of cattle.
Humans can become infected by contaminated water or foods, inadequately cooked meat and dairy products, direct contact with animals and by person-to-person spread.
Symptoms include nausea, vomiting and diarrhoea.
In 1996 the O157 strain of the bug killed 21 elderly people in Wishaw, Lanarkshire, during the world's worst recorded instance of E.coli poisoning.


","How many people were ill?
","{'answer_start': [0], 'text': ['Seven']}"
27,Contamination Question Answering,"Seven people, some of them children, have been diagnosed with E.coli 0157 in a single village.
A further eight people who share the same private water supply are also being tested for the infection.
The water is shared by eight homes in Auchinclech, near Westhill in Aberdeenshire.
Two of the affected people were treated at Aberdeen Royal Infirmary and have now been discharged. The remainder were seen by their GPs.
Health officials at NHS Grampian said the infection was not affecting public water supplies.
A spokesman said: ""None of those affected are currently giving cause for concern.""
Householders in the affected homes are being advised to boil their water while the inquiry to identify the source of the infection continues.
Dr Helen Howie, a consultant in public health medicine at NHS Grampian, said: ""A letter went out to all residents last night to let them know what is going on.""
She added that investigators were examining whether heavy rainfall in the area in recent weeks could have led to the outbreak.
Dr Howie said: ""This outbreak highlights the risks associated with private water supplies.
""Such supplies are liable to bacteriological contamination causing infections such as E.coli O157.
""Householders are encouraged to contact the Environmental Health Service and seek advice on how to improve their supply.""
E.coli O157 is most commonly found in the intestines of cattle.
Humans can become infected by contaminated water or foods, inadequately cooked meat and dairy products, direct contact with animals and by person-to-person spread.
Symptoms include nausea, vomiting and diarrhoea.
In 1996 the O157 strain of the bug killed 21 elderly people in Wishaw, Lanarkshire, during the world's worst recorded instance of E.coli poisoning.


","What are the pathogens?
","{'answer_start': [62], 'text': ['E.coli 0157']}"
25,Contamination Question Answering,"Seven people, some of them children, have been diagnosed with E.coli 0157 in a single village.
A further eight people who share the same private water supply are also being tested for the infection.
The water is shared by eight homes in Auchinclech, near Westhill in Aberdeenshire.
Two of the affected people were treated at Aberdeen Royal Infirmary and have now been discharged. The remainder were seen by their GPs.
Health officials at NHS Grampian said the infection was not affecting public water supplies.
A spokesman said: ""None of those affected are currently giving cause for concern.""
Householders in the affected homes are being advised to boil their water while the inquiry to identify the source of the infection continues.
Dr Helen Howie, a consultant in public health medicine at NHS Grampian, said: ""A letter went out to all residents last night to let them know what is going on.""
She added that investigators were examining whether heavy rainfall in the area in recent weeks could have led to the outbreak.
Dr Howie said: ""This outbreak highlights the risks associated with private water supplies.
""Such supplies are liable to bacteriological contamination causing infections such as E.coli O157.
""Householders are encouraged to contact the Environmental Health Service and seek advice on how to improve their supply.""
E.coli O157 is most commonly found in the intestines of cattle.
Humans can become infected by contaminated water or foods, inadequately cooked meat and dairy products, direct contact with animals and by person-to-person spread.
Symptoms include nausea, vomiting and diarrhoea.
In 1996 the O157 strain of the bug killed 21 elderly people in Wishaw, Lanarkshire, during the world's worst recorded instance of E.coli poisoning.


","What are the symptoms?
","{'answer_start': [1581], 'text': ['nausea, vomiting and diarrhoea']}"
21,Contamination Question Answering,"Seven people, some of them children, have been diagnosed with E.coli 0157 in a single village.
A further eight people who share the same private water supply are also being tested for the infection.
The water is shared by eight homes in Auchinclech, near Westhill in Aberdeenshire.
Two of the affected people were treated at Aberdeen Royal Infirmary and have now been discharged. The remainder were seen by their GPs.
Health officials at NHS Grampian said the infection was not affecting public water supplies.
A spokesman said: ""None of those affected are currently giving cause for concern.""
Householders in the affected homes are being advised to boil their water while the inquiry to identify the source of the infection continues.
Dr Helen Howie, a consultant in public health medicine at NHS Grampian, said: ""A letter went out to all residents last night to let them know what is going on.""
She added that investigators were examining whether heavy rainfall in the area in recent weeks could have led to the outbreak.
Dr Howie said: ""This outbreak highlights the risks associated with private water supplies.
""Such supplies are liable to bacteriological contamination causing infections such as E.coli O157.
""Householders are encouraged to contact the Environmental Health Service and seek advice on how to improve their supply.""
E.coli O157 is most commonly found in the intestines of cattle.
Humans can become infected by contaminated water or foods, inadequately cooked meat and dairy products, direct contact with animals and by person-to-person spread.
Symptoms include nausea, vomiting and diarrhoea.
In 1996 the O157 strain of the bug killed 21 elderly people in Wishaw, Lanarkshire, during the world's worst recorded instance of E.coli poisoning.


","What are the first steps of mitigation?
","{'answer_start': [649], 'text': [' boil their water ']}"
20,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What type of samples were analyzed?
","{'answer_start': [849], 'text': ['faecal specimens']}"
17,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
",What symptoms did people report?,"{'answer_start': [2040], 'text': ['diarrhoea and vomiting']}"
16,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What is the initial cause of the event?
","{'answer_start': [1250], 'text': ['a dead rabbit was found in a treated water tank at the water treatment works']}"
15,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What is the date of the event?
","{'answer_start': [6], 'text': ['June 2008']}"
12,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What is the location of the event?
","{'answer_start': [209], 'text': ['United Kingdom']}"
17,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
",What pathogen was connected to the outbreak?,"{'answer_start': [809], 'text': ['Cryptosporidium ']}"
25,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","How was the event first detected?
","{'answer_start': [16], 'text': ['the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water']}"
17,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","How many people were ill?
","{'answer_start': [1862], 'text': ['23 cases']}"
19,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What are the pathogens?
","{'answer_start': [112], 'text': ['Cryptosporidium oocysts']}"
25,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What are the symptoms?
","{'answer_start': [937], 'text': ['diarrhoea']}"
19,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What is the event?
","{'answer_start': [85], 'text': ['exceedence in the level of Cryptosporidium oocysts found in water']}"
16,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What is the duration of the event?
","{'answer_start': [1769], 'text': ['24 June- 18 July 2008']}"
17,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","From when until when the event happened
","{'answer_start': [2171], 'text': ['24 June- 18 July 2008']}"
26,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
","What are the first steps of mitigation?
","{'answer_start': [389], 'text': ['boil all drinking water']}"
15,Contamination Question Answering,"On 25 June 2008 the local Health Protection Unit was informed by Anglian Water of an exceedence in the level of Cryptosporidium oocysts found in water supplied from the Pitsford Reservoir in Northamptonshire, United Kingdom, during 19 to 24 June 2008 [25]. The reservoir supplied a population of more than 250,000 in the Northampton area. A notice advising people in the affected areas to boil all drinking water was issued on 25 June 2008 and public health messages were circulated to local health services and to the general public via the media. Those members of the public who were concerned about health risks associated with the incident were asked to ring NHS Direct for clinical advice [26]. The HPA wrote to local GPs and hospitals asking them to monitor potential patients for signs and symptoms of Cryptosporidium infection and to submit faecal specimens to the local hospital diagnostic laboratory if patients presented with diarrhoea. Samples from 34 patients where Cryptosporidium infection was identified were sent to the UK Cryptosporidium reference unit for typing. On 30 June 2008, the Cryptosporidium oocysts found in the reservoir water were confirmed as being of the rabbit genotype Cryptosporidium cuniculus [27]. Subsequently, a dead rabbit was found in a treated water tank at the water treatment works. The genotype of Cryptosporidium oocysts in the rabbits large bowel was indistinguishable from that of the oocysts found in the water [27]. After remediation of the water supply and distribution, the boil water notice was lifted on 4 July and the following day the first case of cryptosporidiosis linked to the incident was identified by the reference laboratory (this case was infected with C. cuniculus). During the course of the outbreak (24 June- 18 July 2008, the dates of symptom onset in the first and last case, respectively), 23 cases of cryptosporidiosis were confirmed as being infected with C. cuniculus; one of the 23 was a secondary case. NHS Direct call proportions for gastrointestinal syndromes (diarrhoea and vomiting) for the East Midlands region in England, where Northampton is situated, were examined during the outbreak (24 June- 18 July 2008) and compared with those for England and Wales. 
",What were the associated pathogens of concern?,"{'answer_start': [979], 'text': ['Cryptosporidium ']}"
10,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


",What symptoms were developed?,"{'answer_start': [2707], 'text': ['diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever']}"
14,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What type of samples were analyzed?
","{'answer_start': [619], 'text': ['Water samples']}"
27,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


",What caused the event?,"{'answer_start': [1069], 'text': ['intrusion of wastewater\ninto a drinking water distribution system due to pipe breakage']}"
29,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


",What caused the outbreak?,"{'answer_start': [176], 'text': ['drinking water pipe breakage and subsequent wastewater intrusion into the distribution system']}"
15,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What is the date of the event?
","{'answer_start': [64], 'text': ['2016 (outbreak I) and 2018 ']}"
7,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What is the location of the event?
","{'answer_start': [53], 'text': ['Finland']}"
11,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","How many people were ill?
","{'answer_start': [2575], 'text': ['463 persons']}"
30,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What are the pathogens?
","{'answer_start': [294], 'text': ['sapovirus']}"
24,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What are the symptoms?
","{'answer_start': [2110], 'text': ['abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and feve']}"
28,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What are the initial steps of investigation?
","{'answer_start': [1934], 'text': ['questionnaires']}"
28,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What are the first steps of mitigation?
","{'answer_start': [838], 'text': ['boil water advisory, alternative drinking water sources and chlorination']}"
32,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


","What type of samples were examined?
","{'answer_start': [2333], 'text': ['stool samples']}"
18,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


",How many cases were there?,"{'answer_start': [1882], 'text': ['458']}"
30,Contamination Question Answering,"This study describes two drinking water outbreaks in Finland in 2016 (outbreak I) and 2018 (outbreak II). Both outbreaks caused approximately 450 illness cases and were due to drinking water pipe breakage and subsequent wastewater intrusion into the distribution system. In both outbreaks, the sapovirus was found in patient samples as the main causative agent. In addition, adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides (outbreak II) were detected in patient samples. Water samples were analyzed for the selected pathogens largely based on the results of patient samples. In drinking water, sapovirus and enteropathogenic E. coli (EPEC) were found in outbreak II. As mitigation actions, boil water advisory, alternative drinking water sources and chlorination were organized to restrict the outbreaks and to clean the contaminated distribution network. This study describes two waterborne outbreaks both caused by the intrusion of wastewater
into a drinking water distribution system due to pipe breakage. In outbreak I, the cause of the contamination was a maintenance well containing the air release valves of both drinking water and wastewater pipes. Due to pipe breakage on the road construction site on 12th October 2016, the under pressure in the drinking water network caused the wastewater inflow from the maintenance well through the air release valve into the drinking water distribution system. Mitigation actions during the outbreak included the boil water advisory for two months (from 16th October to 16th December 2016) and chlorination for 50 days (from 16th October to 5th December 2016). When respondents� family members with gastrointestinal illness were taken into account, the estimated number of patients was 458. In order to estimate the magnitude of illness, questionnaires were sent to the households of the contaminated area. The median duration of the symptoms was one to two days and the most frequently reported symptoms included abdominal pain (94%, 101/107), nausea (91%, 100/110), diarrhea (89%, 100/112), abdominal swelling (83%, 86/104), muscular pain (66%, 64/97), vomiting (53%, 52/98) and fever (46%, 42/91). In the acute phase of the outbreak, stool samples were collected from patients between 19th October and 3rd November 2016, and were analyzed in clinical laboratories with routine tests for enteric viruses, pathogenic bacteria, and protozoans (Table 1). During January�February, 463 persons with gastrointestinal illness contacted local primary health care. Symptoms lasted on average for two days and included diarrhea (76%, 352/463), vomiting (65%, 299/463) and fever (32%, 150/463). 


",What were the associated pathogens of concern?,"{'answer_start': [375], 'text': ['adenoviruses and Dientamoeba fragilis (outbreak I), and noroviruses, astroviruses, enterotoxigenic and enterohemorragic Escherichia coli (ETEC and EHEC, respectively) and Plesiomonas shigelloides']}"