Background: In western countries, late-onset asthmatics are more severe than early-onset asthmatics in clinic-based studies. However, whether asthma occurrence rates were higher in late ages than in younger ages was inconclusive. This information is essentially lacking in Asian population.
Methods: The participants were schoolchildren's parents recruited from 94 elementary and middle schools in 2004. A cross-sectional self-administered questionnaire was sent through the children to their parents to survey their respiratory health. We investigated typical asthma symptoms occurring at different ages and subsequent remission or relapse after the first asthma event. Person-years of the participants from birth to the time of survey were used as the denominator.
Results: Among the 25,377 participants consisting of 949,807 total person-years, 860 reported ever having asthma. Highest incidences occurred at ages 0-12 and 36-40 years. The incidence of asthma was higher in males before puberty, and higher in females after puberty, with overall incidences 1.00 and 0.77 per 1000 person-years for females and males, respectively. Participants with late-onset asthma (onset age >12 years) comprised a large portion of adult current asthmatics. More than 52% of persistence or relapse was observed in early-onset asthma (onset age ≤12 years). The younger birth cohort had a more prominent later peak of asthma incidence than the older one.
Conclusions: In Asian population, asthma occurrence showed a U-shape age distribution with a prominent second peak in the thirties. A high proportion of early-onset asthma relapsed and most of late-onset asthma persisted or relapsed in adulthood.