Determinants of the incidence of childhood asthma: a two-stage case-control study.

Extensive literature exists on potential risk factors for childhood asthma. To the authors' knowledge, no investigators have yet attempted to disentangle the effects of those determinants within a single study setting. The authors aimed to evaluate the independent effects of 47 potential determinants (from the prenatal, perinatal, and childhood periods) of asthma development in children within the first 10 years of life. From a Canadian birth cohort of 26,265 children (1990-2002), a 2-stage case-control study was conducted. In the first stage, 20 controls per case were selected from 3 administrative databases. In the second stage, selected mothers were mailed questionnaires for assessment of additional determinants. Increased risks of childhood asthma were found for > or =1 previous diagnosis of bronchopulmonary disease and atopic dermatitis in the child, oxygen administration after birth, prescription of antibiotics within the first 6 months of life, male gender, asthma during pregnancy, use of antibiotics during pregnancy, maternal receipt of social aid, paternal asthma, and asthma in siblings. Protective effects included use of intranasal corticosteroids during pregnancy, having a wood-burning fireplace, having pets in the home prior to the index date, breastfeeding, and day-care attendance. This study allowed the authors to identify, within a single setting, the most influential determinants of childhood asthma among 47 predictors assessed for the prenatal, perinatal, and childhood periods.