The prevalence of asthma has increased worldwide. However, there is only local evidence for changes in incidence. Data from the European Community Respiratory Heath Survey (ECRHS) can be analysed to reconstruct trends in incidence from 1946–1991 in cohorts born between 1946–1971 in 35 areas corresponding to 15 countries. The authors report the time trends in self-reported first occurrence of asthma and its geographical distribution.
All centres completed the same cross-sectional study in 1991–92. A total of 17,613 individuals (63% of those randomly selected) were included. Recall of age of first asthma attack was recorded at an interview at one point in time in subjects aged 20–44 yrs. Relative risk of asthma by cohort was estimated using survival methods with age as the time scale.
Yearly incidence of asthma increased progressively by birth cohort. The relative risks were 1.12 (0.94–1.34), 1.39 (1.17–1.66), 2.01 (1.60–2.51), and 2.33 (1.81–2.98) for the cohorts born in the years 1951–55, 1956–60, 1961–65, and 1966–71, respectively, in comparison with the cohort born in the years 1946–50. The increase occurred concurrently in most of the countries, in both males and females, and both in childhood and adulthood onset asthma.
These results are consistent with a generational increase in asthma incidence during the previous decades (explained by both a period and/or a cohort effect), although some of the findings could be explained by generational increases in asthma diagnosis.