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 doctor-diagnosed asthma and the prevalence of current asthma using data from two cohorts of the Longitudinal Study of Australian Children (LSAC). Methods:We estimated the cumulative incidence of parent-reported ever-diagnosed asthma and the prevalence of current asthma in the infant (aged 0-1 year at baseline) and kindergarten (aged 4-5 years at baseline) cohorts at each of two follow up assessments. 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 doctor-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 years, 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 been given a diagnosis of asthma by age 8-9 years. 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 years. However, the cumulative incidence of ever being diagnosed with asthma continued to rise from birth to age 8-9 years. Analysis of Wave 4 data of the LSAC, and further waves as they become available, will allow us to investigate further changes in these parameters over time. Questions of interest are: (1) Will the plateau in the prevalence of current asthma continue to age 10-11 years and beyond? (2) Will the cumulative incidence of asthma continue to rise? (3) Will the cumulative incidence of asthma and the prevalence of current asthma remain strikingly similar for both cohorts at the ages where the data cross over? 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 of NSW (Ross Trust).