Incidence and prevalence of asthma and allergic rhinitis: a cohort study of Finnish adolescents.

Only limited data are available about the incidence of asthma and allergic rhinitis based on prospective longitudinal studies throughout childhood into adult life. The main purpose of the study was to estimate the incidence rate of asthma and allergic rhinitis from birth to early adulthood. We also estimated the prevalences of these diseases at 16, 22, and 32 years of age. The data were drawn from a follow-up survey of a Finnish urban age cohort (1967 birth cohort, N = 2269) from age 16 to age 32 years. All data were based on self-report. The prevalence of asthma from age 16 to age 32 years changed from 3.0% to 5.0% (males from 3.3% to 4.9%; females from 2.7% to 5.1%); and that of allergic rhinitis from 17.5% to 26.0% (males from 18.7% to 27.8%; females 16.2% to 24.5%), respectively. The overall incidence rate of asthma was approximately 2.1 new cases per 1000 person-years (95% CI = 1.6-2.8). There was a tendency for boys to have a higher incidence rate of asthma than girls in childhood before 16 years of age: gender difference was reversed from period 17 to 22 years of age. In early adulthood (23-32 years), incidence rates were equal in both sexes. The incidence rate for allergic rhinitis in males was 13.4 per 1000 person-years (95% CI- 11.8-14.8), slightly greater than in females, 11.4 (95% CI = 10.1-12.8). Among both genders, the highest incidence rate of allergic rhinitis was between 17 and 22 years. Our study adds to the limited knowledge on the incidence rates of asthma and allergic rhinitis.