Time trends in the incidence and prevalence of asthma in Australian children: a cohort and age-period analysis

Abstract

Background:Knowledge about the incidence and prevalence of asthma in children can help researchers and policy makers predict demand for health care. Objective:To examine time-trends in the cumulative incidence of physician-diagnosed asthma and the prevalence of current asthma in two children’s cohorts followed up over four years. Methods:An infant cohort, initially enrolled at age 0-1 years, and a kindergarten cohort, initially enrolled at age 4-5 years, were followed up 2-yearly over four years in the Longitudinal Study of Australian Children. For each cohort we estimated the cumulative incidence of parent-reported ever-diagnosed asthma and the prevalence of current asthma at each assessment. Cumulative incidence was defined as having reported ever-diagnosed asthma at the current or any preceding assessment. Current asthma was defined as having a parent-reported diagnosis of asthma at or before the assessment and either taking asthma medication and/or having an illness with wheezing that lasted for a week or more in the previous 12 months. Results:At baseline, the infant and kindergarten cohorts comprised 5,107 and 4,983 children respectively, with 83% and 84% followed up after 4 years. At age 4-5, the cumulative incidence of ever diagnosed asthma was almost identical in the infant and kindergarten cohorts, as was the prevalence of current asthma. Almost one-third of children had a diagnosis of asthma by age 8-9. Cumulative incidence of asthma Prevalence of current asthma Age at follow-up (years) Infant Kindergarten Infant Kindergarten 0-1* - 2-3 14.5 12.5 4-5** 22.1 21.1 15.6 15.7 6-7 28.1 17.0 8-9 31.3 17.1 *Baseline period for infant cohort. No question about ever-diagnosed asthma at this assessment. **Baseline period for kindergarten cohort

Conclusions:The prevalence of current asthma increased with age, reaching a plateau at age 6-7. However, the cumulative incidence of ever being diagnosed with asthma continues to rise from birth to age 8-9 years. Acknowledgements: ACAM is an Australian Institute of Health and Welfare collaborating unit, funded by the Department of Health and Ageing. This analysis is funded by the Asthma Foundation.