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 children 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 [+ or -] 3.49 EU/[m.sup.3] (geometric mean [+ or -] geometric SD), and number of annualized illness episodes was 6.83 [+ or -] 2.80 (mean [+ or -] 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, environmental tobacco smoke, child care attendance, indoor temperature, and income. Indoor mold surface 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, housing, respiratory illness. doi:10.1289/ehp.8142 available via http://dx.doi.org/[Online 3 November 2005]

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Endotoxins are lipopolysaccharide components of the outer membranes of gram-negative bacteria. Endotoxin has been implicated in bysinnosis, 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 reductions 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 illnesses 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 influence of indoor environmental factors on respiratory 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 boards of the Ottawa Hospital and the Health Protection Branch of the Canadian government. Recruitment occurred during the late autumn and winter (cold season) of each year when the ground was frozen. Because of resource constraints, we recruited approximately 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 telephone 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 sociodemographics 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. …