Age at asthma diagnosis in subjects with and without allergic rhinitis.

Background: Onset of allergic asthma has a strong association with childhood. Much less is known about adult onset asthma and its association with allergy. Objectives: To assess the proportion of allergic and non-allergic asthma in adulthood in relation to the age at asthma diagnosis. Methods: Postal questionnaires were sent to 8000 randomly selected recipients aged 20-69 years in Finland in 2016. The participation rate was 52% (n=4173). Asthma was classified allergic when a physician-diagnosed asthma and a physician-diagnosed allergic rhinitis were both reported. Results: The prevalence of physician-diagnosed asthma and allergic rhinitis were 11% (n=445) and 18%, respectively. Mean ages at diagnosis of allergic asthma and non-allergic asthma were 19 and 35 years, respectively. Among subjects with asthma diagnosis at ages 0-19, 20-39 and 50-69 years, 67%, 55% and 23%, respectively, were allergic. For non-allergic asthma, the incidence rate of asthma was lowest in children and young adults (0.7/1000/year). It increased after middle age and was highest in older age groups (2.4/1000/year in 50-59 years old). Conclusions: The study results support the well-recognized fact that childhood asthma is mostly allergic. To our knowledge, this is the first study to show that the proportion of allergic asthma steadily declines with advancing age at asthma diagnosis and non-allergic asthma becomes the dominant phenotype with asthma diagnosed in middle age.