The prevalence of and risk factors for atopy in early childhood: a whole population birth cohort study.

A birth cohort was followed-up to age 4 years to record the development of allergic disorders and to study the influence of genetic and environmental factors. Information on family history and environmental factors was obtained at birth, and serum cord IgE was measured. At age 4 years, 1218 children were reviewed. By age 4 years, 27% of the children had symptoms of allergic disease. Period prevalence of asthma increased from 8.7% in infancy to 14.9% at 4 years. Family history of atopy was the single most important risk factor for atopy in children. Sibling atopy was a stronger predictor of clinical disease than maternal or paternal atopy, whereas paternal atopy, male sex, and high cord IgE were significant for the development of allergen sensitization. Children of asthmatic mothers were three times more likely to have asthma (odds ratio [OR]: 3.0, 95% confidence interval [CI]: 1.6-5.8) and rhinitis (OR: 2.9, CI: 1.1-7.4). Formula feeding before 3 months of age predisposed to asthma at age 4 years (OR: 1.8, CI: 1.2-2.6). The effect of maternal smoking on childhood wheeze seen at 1 and 2 years was lost by age 4, except for a subgroup with negative skin test responses (nonatopic asthma). Less than half (46%) of the infantile wheezers were still wheezing at 4 years of age. Family history of atopy remains the most important risk factor for atopy in children, but other markers can be identified with a potential for intervention at an early age.