Infections in early childhood and risk of atopic disease.

Having more siblings has been shown to be associated with lower risk of atopic diseases. This might be due to the higher number of infections in larger families. Because children attending day care centres have more respiratory infections, we analysed the association of number of siblings and day care attendance in children aged 1-3 y with atopic disease in a cross sectional survey of 8387 schoolchildren aged 13-14 y and their parents in four regions of Finland. Having no siblings, compared to three or more siblings, was associated with significantly higher risk of lifetime history of hay fever (odds ratios (OR) 1.53, 95% confidence interval (CI) 1.25-1.86) and atopic eczema (OR 1.28, 95%CI 1.04-1.56), and higher risk (ns) of doctor-diagnosed asthma ever (OR 1.26, 95%CI 0.85-1.88). Less strong associations were observed with the number of older siblings (birth order). No associations were observed with current symptoms of these diseases during the last 12 mo. Attending a day care centre at the age of 1-3 y was not associated with decreased risk of any of the atopic diseases studied, but, in contrast to the hypothesis, was associated with slightly increased risk of current symptoms of hay fever (OR 1.34, 95%CI 1.12-1.60). The present results suggest that other factors than early childhood respiratory infections explain the association between number of siblings and future risk of atopic disease.