Research | Children’s Health Airborne Endotoxin Is Associated with Respiratory Illness in the First 2 Years of Life Robert Dales,1 David Miller,1 Ken Ruest,2 Mireille Guay,1 and Stan Judek 1 1Air Health Effects Division, Health Canada, Ottawa, Ontario, Canada; 2Research Division, Canada Mortgage and Housing Corporation, Ottawa, Ontario, Canada To determine the inﬂuence of endotoxin on the incidence of acute respiratory illness during the ﬁrst 2 years of life, we carried out a longitudinal follow-up study, beginning at birth, of 332 chil- dren born in Prince Edward Island, Canada. We measured 5-day averaged air endotoxin in the homes of children, whose parents provided information by daily symptom diaries and twice- monthly telephone contact for up to 2 years. Endotoxin concentration was 0.49 ± 3.49 EU/m3 (geometric mean ± geometric SD), and number of annualized illness episodes was 6.83 ± 2.80 (mean ± SD). A doubling of the air endotoxin concentration was associated with an increase of 0.32 illness episodes per year (p = 0.0003), adjusted for age, year of study, breast-feeding, environ- mental tobacco smoke, child care attendance, indoor temperature, and income. Indoor mold sur- face area and fungal ergosterol were not significantly associated with endotoxin. Airborne endotoxin appears to be a risk factor for clinically symptomatic respiratory illnesses during the ﬁrst 2 years of life independent of indoor fungus. Key words: bacteria, children, endotoxin, hous- ing, respiratory illness. Environ Health Perspect 114:610–614 (2006). doi:10.1289/ehp.8142 available via http://dx.doi.org/ [Online 3 November 2005] Endotoxins are lipopolysaccharide components of the outer membranes of gram-negative bac- teria. Endotoxin has been implicated in bysin- nosis, organic dust toxic syndrome, and illness in swine confined animal feeding operations workers (Douwes et al. 2002). Endotoxin in settled dust in residential environments has been associated with an increase in asthma symptoms, asthma medications, and reduc- tions in lung function in those with atopy or asthma (Douwes et al. 2000; Gehring et al. 2001a; Michel et al. 1991, 1996; Park et al. 2001a; Rizzo et al. 1997). Despite these adverse effects, early exposure may reduce future allergies and asthma (Lapa e Silva et al. 2000; Litonjua et al. 2002; Reed and Milton 2001; Von Ehrenstion et al. 2000; Von Mutius et al. 2000). Most studies were of adults or school-age children, with two focusing on infants. In the present study we examined the association between airborne endotoxin and the incidence of respiratory ill- nesses in children during the first 2 years of life. We accounted for exposure to a potential confounder, indoor fungus, which has been associated with respiratory symptoms and may be associated with the presence of indoor endotoxin (Gehring et al. 2001b; Verhoeff and Burge 2004). Materials and Methods Study design. Data for the present study were abstracted from an ongoing study of the inﬂu- ence of indoor environmental factors on respi- ratory illness during the first 2 years of life. The study began in 1997 in the province of Prince Edward Island, Canada, which has a population of approximately 150,000. The study was approved by the ethics review 610 boards of the Ottawa Hospital and the Health Protection Branch of the Canadian govern- ment. Recruitment occurred during the late autumn and winter (cold season) of each year when the ground was frozen. Because of resource constraints, we recruited approxi- mately 60 consecutive newborns each year. All physicians who practice obstetrics in the province participated in recruitment. Women in the third trimester of pregnancy received letters from the physicians’ ofﬁces describing the study and requesting participation. Interested women were contacted by tele- phone to obtain informed consent. Excluded from the study were babies born > 4 weeks premature, those with neonatal respiratory difﬁculties requiring prolonged hospitalization at birth, and those whose families expected to change residence within 2 years of birth. Only one child per household was studied. Baseline information was obtained on sociodemo- graphics and family history. The participating parents maintained a daily symptom diary from birth until 2 years or until the study ended, on large multipurpose calendars. Each study family was phoned twice monthly to document information from the diary. If par- ents had omitted recording symptoms on a daily basis, they provided information for the previous 2 weeks based on recall. Parental reporting of child care attendance was also recorded every 2 weeks. Definition of respiratory illness. We adapted the method of Samet et al. (1992) to deﬁne a respiratory illness episode, the purpose being to identify discrete acute illnesses as opposed to persistent ongoing symptoms, such as a chronically runny nose. We defined the beginning of an illness episode as 2 consecutive days with any one of the four following symp- toms: stuffy nose, cough, wheeze, and short- ness of breath. The illness episode starts on the ﬁrst of these 2 consecutive days and ends when there are 2 consecutive days with none of these symptoms, the last day of the illness episode being the last day with a symptom. The primary outcome of interest was the number of illness episodes prorated on an annual basis (number multiplied by 365/days of observation). A secondary outcome meas- ure, illness days, was deﬁned as the sum of all days occurring within illness episodes, also prorated on an annual basis. For example, if a child had two illness episodes each lasting 3 days, six illness days would be assigned. If a child had two illness episodes each lasting 5 days, 10 illness days would be assigned. Air sampling for endotoxin and ergosterol. Sampling was done within the ﬁrst year of birth, and for 81%, within the first 4 months. Air from the child’s bedroom was sampled for both endotoxin and ergosterol through a three-piece cartridge equipped with a polycarbonate ﬁlter for approximately 5–7 days with a Buck model SS sampling pump (AP Buck, Orlando, FL, USA) calibrated at 2 L/min at the beginning and end of the sampling. Forty-eight hours after the pump was installed, the flow rate was checked to ensure it was within 5% of the ini- tial reading. Very high dust concentrations can clog the ﬁlter and reduce the pump ﬂow. If this happened, the pump was stopped and air endo- toxin concentration was calculated based on the reduced sampling time. The total volume of air sampled ranged from 6.0 to 23.9 m3, limited by the need to maintain an acceptable flow rate. Once collected, the cartridges and ﬁlters were sealed in new plastic bags and stored at room temperature under dry conditions. For endotoxin analysis, the filters were extracted with depyrogenated water (LRW, Address correspondence to R. Dales, Ottawa Hospital (General Campus), 501 Smyth Rd., Box 211, Ottawa, Ontario K1H 8L6, Canada. Telephone: (613) 737-8198. Fax: (613) 739-6266. E-mail: rdales@ottawahospital.on.ca This work is supported by Health Canada, Canada Mortgage and Housing Corporation, Prince Edward Island Reproductive Care Program, Prince Edward Island Medical Society, Carleton University, and Prince Edward Island Department of Health and Social Services. The authors declare they have no competing ﬁnancial interests. Received 23 March 2005; accepted 3 November 2005. VOLUME 114 | NUMBER 4 | April 2006 • Environmental Health Perspectives