Examining Trends in the Incidence of Asthma in Children in Ontario

Background: The causes of trends in asthma incidence are not fully understood. Objectives: This study examined trends in age and severity at asthma diagnosis for Ontario children. Methods: Multiple birth cohorts of Ontario children between 1992-2000 were created using health administrative data. Descriptive statistics and multivariable logistic regression examined changes in age and severity of asthma at diagnosis over time. Results: Age at asthma diagnosis decreased (p<0.0001) with a higher relative risk of asthma in children under age three (RR=1.5, 95% CI:1.47, 1.54). Predictors of asthma diagnosis before three included male sex, lower income quintile, and maternal asthma. ‘Severe onset asthma’ increased over time (p