Early Life Factors Associated with Incidence of Physician-diagnosed Asthma in Preschool Children: Results from the Canadian Early Childhood Development Cohort Study

Background. Asthma is a common childhood illness. The objective of this study is to determine the incidence of physician-diagnosed asthma in preschool years and its relationship to host, prenatal and postnatal factors, early childhood factors, parental factors, household factors and demographic factors. Methods. The study sample was comprised of 8,499 infants and toddlers (<2 years at baseline) enrolled in the Canadian Early Childhood Development Study. Incidence of asthma was determined when the children were in preschool age (2 to 5 years). Results. The 4-year cumulative incidence at preschool age was 13.7% for physician-diagnosed asthma. History of early childhood wheezing before 2 years of age was a significant risk factor for incidence of asthma in preschool years (hazard ratio (HR): 2.32; 95% confidence interval (CI): 2.04–2.65). Factors that were protective for the development of asthma were breastfeeding more than 3 months (HR: 0.82; 95% CI: 0.69–0.97); history of nose or throat infection often in...