High prevalence of severe asthma in a large random population study

Background: The prevalence of asthma severity is not well described at a population level. Objective: We sought to determine the prevalence of phenotypic signs of asthma severity among asthmatic patients in a general population and to describe risk factors for asthma severity. Methods: We performed an epidemiologic study conducted between 2008 and 2012 (West Sweden Asthma Study). A postal questionnaire was sent to a random population (n 5 30,000) in west Sweden, with 18,087 responses. A total of 2,006 subjects were carefully phenotyped. Only subjects with `` active asthma'' (symptoms or medication in the last year, n 5 744) were analyzed in this study to determine the degree of severity of the disease within an asthma cohort. Phenotypes of severity were calculated based on (1) multiple symptoms during the day despite ongoing use of asthma medications, (2) FEV1 of less than 70% of predicted value, (3) daily or almost daily use of rescue medications, (4) nighttime symptoms once a week or more, and (5) oral corticosteroid use/emergency department visits. Asthmatic patients were grouped as having nonsevere disease, 1 sign of severity, or 2 or more signs of severity. Results: A total of 36.2% of asthmatic patients expressed at least 1 sign of asthma severity, and 13.2% had 2 or more signs. The group with 2 or more signs was older in age and had higher body mass index, a higher rate of tobacco smoking, and lower lung function. Bronchial hyperreactivity, airway inflammation, and sensitization were significantly different among the 3 groups. At a population level, the prevalence of asthma severity was 3.1% for 1 sign and 1.3% for at least 2 signs. Conclusion: More than 1 in 3 asthmatic patients show at least 1 sign of asthma severity. The phenotypes of asthma severity are highly diverse, which is important to consider when implementing personalized medicine in asthmatic patients.