Secular trends of allergic asthma in Danish adults. The Copenhagen Allergy Study

AbstractNumerous studies have reported increases in asthma prevalence among children world-wide. Less is known about similar trends in adults. We aimed to investigate whether the prevalence of allergic asthma symptoms had increased in an adult general population.Two cross-sectional surveys using identical methods were carried out in 1989 and 1998. A one-page questionnaire on respiratory symptoms was mailed to random samples of 15–41-year-olds living in Copenhagen. The response rates were 86·6% (3624/4185) and 78·8% (2402/3048) in 1989 and 1998, respectively. The questionnaire was validated with specific immunoglobilin E (IgE) positivity as the reference in a random sample of responders in connection with both surveys.We found a significantly increased prevalence of subjects who reported shortness of breath on exposure to pollens (6·6%vs. 10·3%, odds ratio 1·61, 95% CI 1·34–1·95), furry animals (5·4%vs. 7·6%, odds ratio 1·45, 95% CI 1·17–1·79), and house dust (7·8%vs. 10·2%, odds ratio 1·35, 95% CI 1·12–1·61). The validation of these symptoms showed that the positive predictive values were reasonably stable over time, which may support that a true increase in allergic asthma has occurred.In conclusion, the prevalence of allergic asthma symptoms increased significantly in this adult general population over a 9-year period