viral respiratory infections , particularly in young children and the elderly 
 , can lead to substantial morbidity , such as increased rates of lower respiratory tract infections and hospitalization . 
 , 
  relatively few prospective , communitybased studies to define etiologic agents for respiratory infection have been reported . , 
 , 
  moreover , existing studies are limited in that most are not prospective communitybased studies 
 , 
  and did not use highly sensitive diagnostic testing such as rtpcr . data are particularly sparse on the epidemiology of respiratory viruses other than influenza , respiratory syncytial virus ( rsv ) , and parainfluenza , 
 , 
  and most of these studies are based on culture , antigen testing or serology that are less sensitive and specific relative to molecular assays . with the exception of influenza , specific vaccines or antiviral medications are either not widely available or have not proved effective for respiratory viral infections . nevertheless , as vaccine development evolves and new therapeutic agents are produced , characterizing the epidemiology of viral respiratory infections will delineate the appropriate populations in whom these agents should be targeted . furthermore , this could lead to better insights concerning those at highest risk for bacterial superinfection following viral infection . hutterites live in british columbia , alberta , saskatchewan , and manitoba , as well as several northcentral american states where they practice communal farming on small colonies of typically 80120 people , relatively isolated from towns and cities . however , outbreaks of respiratory infection in hutterite colonies occur regularly , as viruses are introduced from exposure to people outside the community . as the colonies are not very large , it is possible to obtain detailed demographic , health , and immunization information from all members . the implementation of a cluster randomized trial aimed at reducing influenza in the canadian hutterite community allowed us to prospectively collect data on other respiratory viruses . in this report , we sought to determine agespecific incidence of laboratoryconfirmed respiratory virus infection occurring in the hutterite community and to document the temporal relationship of virusspecific attack rates . participants were 3273 community members of 46 hutterite colonies from alberta , saskatchewan , and manitoba who were enrolled in a cluster randomized trial ( september 22 to december 23 , 2008 ) . 
  by randomizing children in the hutterite colonies to either trivalent inactivated influenza vaccine or hepatitis a vaccine , as a control , the trial was designed to determine the indirect effectiveness of influenza vaccine on unimmunized residents . the present data are based on the first year of the trial where children in colonies allocated to influenza vaccine received the vaccine recommended for the 20082009 influenza season ( a / brisbane/59/2007 [ h1n1]like virus , a / brisbane/10/2007 [ h3n2]like virus , b / florida/4/2006like virus ; vaxigrip , sanofi pasteur , lyon , france ) . as previously described , participants were assessed for signs and symptoms of respiratory illness over the followup period , defined by the start date ( > 1 laboratoryconfirmed influenza case in two consecutive weeks from sentinel sites ) and stop date ( no laboratoryconfirmed influenza cases for two consecutive weeks in the sentinel sites ) . 
  this period extended from december 28 , 2008 , until june 23 , 2009 . research nurses assessed all study participants twice weekly using a standardized checklist of selfreported symptoms or signs from study participants or parents . one representative from each household ( e.g. , the mother ) was designated to complete the checklist for all family members and provide this when the research nurse made a site visit . if anyone reported new symptoms , the nurse interviewed the study participant to confirm their symptoms and date of onset . a nasopharyngeal specimen was obtained if two or more of the following symptoms were present : fever ( 38c ) , cough , nasal congestion , sore throat , headache , sinus problems , muscle aches , fatigue , ear ache or infection , or chills . research nurses would also contact the household representative if the selfreported checklists were incomplete , to followup on missing data . influenza was detected using the centers for disease control and prevention s human influenza virus realtime rtpcr detection and characterization panel , which targets the matrix gene for influenza a and nonstructural gene for influenza b. respiratory viruses were detected using a rtpcr method ( xtag rvp assay ; luminex , tx , usa ) . this assay detects coronavirus 229e , nl63 , oc43 , parainfluenza virus type 1 , 2 , 3 , 4 , entero / rhinovirus , respiratory syncytial virus a and b , human metapneumovirus , and adenovirus . all 3273 participants were kept in the analyses for noninfluenza viruses . however , to reduce the potential for biased estimates , 1945 participants who either individually received influenza vaccine or were in study colonies assigned to the intervention arm ( influenza vaccine ) were excluded from the analysis for seasonal influenza virus infection , leaving 1328 participants for the analysis . to calculate incidence , we counted only the first viral infection for a specific virus , as the numerators ( agespecific ) , while the denominators were agespecific persondays , which included the entire period of surveillance for participants who were not infected with the specific virus along with the persondays up to the point of infection for those who were infected . if a participant was swabbed more than once within 14 days , and if the same virus was detected on 1 occasion in this time frame , then only the first episode detected was used in the analysis . to quantify the temporal relationship between the respiratory viruses , we defined an epidemic midpoint as the date when 50% of the cumulative cases of virus detected were reached over the period of surveillance . we calculated incidence using events per 1000 persondays and estimated differences in rates assuming a poisson distribution . participants were 3273 community members of 46 hutterite colonies from alberta , saskatchewan , and manitoba who were enrolled in a cluster randomized trial ( september 22 to december 23 , 2008 ) . 
  by randomizing children in the hutterite colonies to either trivalent inactivated influenza vaccine or hepatitis a vaccine , as a control , the trial was designed to determine the indirect effectiveness of influenza vaccine on unimmunized residents . the present data are based on the first year of the trial where children in colonies allocated to influenza vaccine received the vaccine recommended for the 20082009 influenza season ( a / brisbane/59/2007 [ h1n1]like virus , a / brisbane/10/2007 [ h3n2]like virus , b / florida/4/2006like virus ; vaxigrip , sanofi pasteur , lyon , france ) . as previously described , participants were assessed for signs and symptoms of respiratory illness over the followup period , defined by the start date ( > 1 laboratoryconfirmed influenza case in two consecutive weeks from sentinel sites ) and stop date ( no laboratoryconfirmed influenza cases for two consecutive weeks in the sentinel sites ) . 
  this period extended from december 28 , 2008 , until june 23 , 2009 . research nurses assessed all study participants twice weekly using a standardized checklist of selfreported symptoms or signs from study participants or parents . one representative from each household ( e.g. , the mother ) was designated to complete the checklist for all family members and provide this when the research nurse made a site visit . the nurse would review the checklist . if anyone reported new symptoms , the nurse interviewed the study participant to confirm their symptoms and date of onset . a nasopharyngeal specimen was obtained if two or more of the following symptoms were present : fever ( 38c ) , cough , nasal congestion , sore throat , headache , sinus problems , muscle aches , fatigue , ear ache or infection , or chills . research nurses would also contact the household representative if the selfreported checklists were incomplete , to followup on missing data . influenza was detected using the centers for disease control and prevention s human influenza virus realtime rtpcr detection and characterization panel , which targets the matrix gene for influenza a and nonstructural gene for influenza b. respiratory viruses were detected using a rtpcr method ( xtag rvp assay ; luminex , tx , usa ) . this assay detects coronavirus 229e , nl63 , oc43 , parainfluenza virus type 1 , 2 , 3 , 4 , entero / rhinovirus , respiratory syncytial virus a and b , human metapneumovirus , and adenovirus . all 3273 participants were kept in the analyses for noninfluenza viruses . however , to reduce the potential for biased estimates , 1945 participants who either individually received influenza vaccine or were in study colonies assigned to the intervention arm ( influenza vaccine ) were excluded from the analysis for seasonal influenza virus infection , leaving 1328 participants for the analysis . to calculate incidence , we counted only the first viral infection for a specific virus , as the numerators ( agespecific ) , while the denominators were agespecific persondays , which included the entire period of surveillance for participants who were not infected with the specific virus along with the persondays up to the point of infection for those who were infected . if a participant was swabbed more than once within 14 days , and if the same virus was detected on 1 occasion in this time frame , then only the first episode detected was used in the analysis . to quantify the temporal relationship between the respiratory viruses , we defined an epidemic midpoint as the date when 50% of the cumulative cases of virus detected were reached over the period of surveillance . we calculated incidence using events per 1000 persondays and estimated differences in rates assuming a poisson distribution . approximately , 40% of participants were 15  years of age or younger and comorbidity was infrequent . 362 ( 11% ) were aged 04  years , 366 ( 11% ) aged from 5 to 8  years , 574 ( 18% ) aged from 9 to 14  years , 310 ( 10% ) aged from 15 to 19  years , 410 ( 13% ) aged from 20 to 29  years , 380 ( 12% ) from 30 to 39  years , 409 ( 13% ) from 40 to 49  years , and 462 ( 14% ) aged 50  years . there were 149 ( 112% of 1328 ) with laboratoryconfirmed influenza and 595 ( 182% of 3273 ) with at least 1 episode of laboratoryconfirmed respiratory viral infection other than influenza . of the 149 with laboratoryconfirmed influenza , 32 were also infected with another respiratory virus . influenza ( including a ( h1n1 ) , a ( h3n2 ) , and b ) had the highest incidence ( 080/1000 persondays ci : 074087 ) , followed by entero / rhinovirus ( 069/1000 persondays , ci : 065073 ) , rsv ( 028/1000 persondays , ci : 025030 ) , coronaviruses ( 026/1000 persondays ) , and parainfluenza ( 023/1000 persondays ) . the age group  specific incidence of respiratory virus infection is shown in figure  1 . among children of age < 5 , entero / rhinovirus had the highest incidence ( 136/1000 persondays ; ci : 120153 ) , but this was not significantly higher than rsv ( 129/1000 persondays , ci : 112145 ) , p  =  0809 ) . influenza b was not detected among those aged 30 and among those 4049 years of age and older , a decline in incidence was observed for entero / rhinovirus , coronaviruses , rsv , and influenza a. the incidence of parainfluenza increased among those aged 4049  years and older ; in contrast , hmpv ( human metapneumovirus ) was not detected in those 2029  years of age or older ( figure  1 ) . in addition , the highest incidence of parainfluenza was in children aged 04  years ( 111/1000 persondays , ci : 095126 ) . specific incidences of respiratory viruses , including seasonal influenza , during the influenza season per 1000 persondays . entero / rhinovirus had the highest agespecific incidence among participants with age 50 ( 033/1000 persondays , ci : 026040 ) , which was higher than for seasonal influenza ( 025/1000 persondays , ci : 014036 ) , although statistically not significant , p  =  0744 ) ( figure  1 ) . the incidence of entero / rhinovirus in this age group was significantly higher than coronavirus ( 027/1000 persondays , ci : 021033 , p  =  001 ) and to rsv ( 006/1000 persondays , ci : 003009 , p  =  0005 ) . the weekly occurrence of influenza and noninfluenza viruses was plotted in bar graphs ( figure  2 ) . the epidemic midpoint for seasonal influenza was march 23 , 2009 , whereas individual date values for influenza a ( h1n1 ) , a ( h3n2 ) , and b were march 9 , april 7 , and april 18 , respectively . for coronaviruses , parainfluenza viruses , entero / rhinovirus , rsv , and hmpv these values were march 2 , march 2 , april 30 , march 9 , and march 27 , respectively . periods of occurrence and numbers of cases of respiratory viruses by cdc weeks during the influenza season 20082009 . the periods of occurrence for each virus are indicated by a horizontal line with the corresponding epidemic midpoint identified by a black circle . there are few prospective communitybased surveillance data on the circulation of noninfluenza viruses during the influenza season . in the hutterite communities we studied , a high attack rate of influenza was followed by entero / rhinovirus and then by rsv , coronavirus and parainfluenza . most respiratory viruses had their highest incidence in children aged 08 , except coronaviruses and h1n1 seasonal influenza , which had the highest incidence in ages 4049 and 1519 , respectively ( figure  1 ) . coronaviruses occurred among persons in all age groups . typically , rsv is the most common respiratory virus identified in hospitalized children under the age of 5  years . , 
 , 
 , 
  the fact that the virus with the highest attack rate in children under the age of five was entero / rhinovirus and not rsv was unanticipated even though the difference in incidence between the two was not statistically significant . it may be explained by the fact that entero / rhinovirus has a wide spectrum of disease and milder cases in our communitybased study were detected . previous studies have reported hospitalized children with lower respiratory tract disease or severe pneumonia , 
 , 
  emphasizing the predilection of rsv to lead to hospitalization , but not reflecting a dominant circulating virus in the community . our findings also suggest that the incidence of entero / rhinovirus infection in the community has been underestimated . the high incidence of entero / rhinovirus we detected might also be related to our use of rtpcr , which yields a substantially higher sensitivity compared to conventional culture . the codominance of entero / rhinovirus with influenza in this study is consistent with a recent study reporting a high incidence of entero / rhinoviruses during the influenza season . our data suggest that entero / rhinovirus may be more common in the elderly than previously recognized , because entero / rhinovirus had the highest agespecific incidence among participants with age 50 . the relatively high incidence of entero / rhinovirus and coronavirus compared to rsv in this age group is in keeping with a previous report that included an elderly population 
 . parainfluenza is generally reported as the second most common virus after rsv to cause lower respiratory tract diseases in young children . in contrast , parainfluenza was less common in our study than influenza , entero / rhinovirus , coronaviruses , and rsv . the highest incidence was , however , in children aged 04 . from a clinical perspective , the high degree of cocirculation of other respiratory viruses along with influenza as shown in figure  2 raises the question of the degree to which signs and symptoms of respiratory infection are falsely attributed to influenza , which has implications for the empiric use of antivirals . a consistent finding across all respiratory viruses was that the highest incidence was in children aged 04  years or from 5 to 8  years . the incidence generally decreases in teenaged participants and in young adults and then either reaches a plateau or increases slightly with advanced age . this could be explained by the higher incidence of viral respiratory infection in age < 5 compared to older individuals , but also by the lower detection rate of respiratory virus in the elderly due to reduced viral shedding in older age groups . influenza b infection , unlike influenza a , was not observed among adults > 30 . the most likely explanation is due to the relative conservation of influenza b immunity in older individuals , as previously reported . , 
  the incidence of entero / rhinovirus and coronavirus infection in older individuals was relatively higher than that of other viruses , consistent with previous studies . first , the respiratory virus test is performed only within symptomatic participants during the influenza season , and the respiratory virus shedding in asymptomatic control is not evaluated . second , because the study is performed during the 20082009 influenza season , it potentially underestimates the annual incidence of respiratory viruses other than influenza which may have different season or which may cause biannual epidemic . third , it is performed in hutterite colonies that do not represent the general population of canada . another limitation is that there were three colonies dropped out of the study after randomization . however , as the characteristics of these colonies do not differ from those of the 46 colonies that participated the study , we consider this did not affect the results . in conclusion , there were multiple cocirculating viruses over the influenza season . agespecific incidence of respiratory viruses was highest in young children but with unexpected high incidence of entero / rhinovirus in this group . tae hyong kim wrote this manuscript as first author and involved in data collection and analysis . margaret l. russell and kevin fonseca designed the study and involved in data collection , the writing and major revision of this manuscript , final approval . gregory horsman , paul van caeseele , khami chokani , mark voight , lorraine moss richard webby , and cassandra howse involved with data collection , writing , and major revision . lorne babiuk , david j. d. earn , pardeep singh , and fred aoki involved with analysis , writing , and major revision . mark loeb designed the study and involved in data collection , the writing and major revision of this manuscript . department of pathology and molecular medicine , mcmaster university , hamilton , ontario , canada . division of infectious diseases , departments of internal medicine , soon chun hyang university seoul hospital , seoul , republic of korea . department of community health sciences , university of calgary , alberta , canada . provincial laboratory for public health and department of microbiology and infectious diseases , calgary , alberta , canada . judes children s research hospital , memphis , tennessee , usa . department of mathematics and statistics , mcmaster university , hamilton , ontario , canada . michael g. degroote institute for infectious disease research , mcmaster university , hamilton , ontario , canada . department of clinical epidemiology and biostatistics , mcmaster university , hamilton , ontario , cananda .
please cite this paper as : kim et  al . 
 ( 2012 ) characteristics of respiratory viral infections during influenza season in canadian hutterite communities . 
 influenza and other respiratory viruses doi:10.1111/irv.12021 . 
 objectives :   to determined the pathogenspecific incidence of respiratory virus infection in hutterite communities occurring over the 20082009 influenza season and assess temporal characteristics of respiratory illness related to infection . 
 methods :   3273 participants community members enrolled in a cluster randomized trial of influenza vaccine were studied . 
 results :   one hundred fortynine participants had laboratoryconfirmed influenza , and 595 had at least one episode of laboratoryconfirmed respiratory viral infection other than influenza . 
 entero / rhinovirus had the highest incidence among children < 5 years . 
 conclusions :   a decline in the incidence of infections with age was observed for influenza as well as for most other respiratory viruses .