Objective. To estimate the effects of the type of day care on respiratory health in preschool children.Methods. A population-based cross-sectional study of Oslo children born in 1992 was conducted at the end of 1996. A self-administered questionnaire inquired about day care arrangements, children's health, environmental conditions, and family characteristics ( n = 3853; response rate, 79%).Results. In logistic regression controlling for confounding, children in day care centers had more often nightly cough (adjusted odds ratio, 1.89; 95% confidence interval, 1.34–2.67), and blocked or runny nose without common cold (1.55; 1.07–1.61) during the past 12 months compared with children in home care. Poisson regression analysis showed an increased risk of the common cold (incidence rate ratio, 1.21; 1.12–1.30) and otitis media (1.48; 1.22–1.80), and the attributable proportion was 17.4% (95% confidence interval, 10.7–23.1) for the common cold and 32.4% (18.0–44.4) for otitis media. Early starting age in the day care center increased the risk of developing recurrent otitis media. Also the lifetime risk of doctor-diagnosed asthma was higher in children who started day care center attendance during the first 2 years of life.Conclusions. Attendance to day care centers increases the risk of upper respiratory symptoms and infections in 3- to 5-year-old children. The starting age seems to be an important determinant of recurrent otitis media as well as asthma. The effect of day care center attendance on asthma is limited to age up to 2 years. This effect is most likely mediated via early respiratory tract infections that are substantially more common in children in day care centers compared with children in home care.
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