Severe asthma among adults: Prevalence and clinical characteristics

Background: Severe asthma is a considerable challenge for patients, health care professionals and society. Few studies have estimated the prevalence of severe asthma according to modern definitions of which none based on a population study. Methods: We estimated the prevalence and studied characteristics of severe asthma in a large adult population-based asthma cohort followed for 10-28 years in northern Sweden: 1006 subjects participated in a follow-up during 2012-14, when 830 (82.5%) still had current asthma (mean age 59y, 32-92y, 56% women). Severe asthma was defined according to three internationally well-known criteria: the US SARP, ATS/ERS and GINA. All subjects with severe asthma were undergoing respiratory specialist care, and were also contacted by telephone to verify adherence to treatment. Results: The prevalence of severe asthma according to the three definitions was 3.6% (US SARP), 4.8% (ERS/ATS), and 6.1% (GINA) among subjects with current asthma. Although all were using high ICS doses and other maintenance treatment, >40% had uncontrolled asthma and <10% had controlled asthma according to the ACT. Severe asthma was related to age >50 years, nasal polyposis, decreased FEV1, not fully reversible airway obstruction, sensitization to aspergillus, elevated neutrophils and partly to eosinophils, and tended to be more common in women. Conclusion: The prevalence of severe asthma in this asthma cohort was 4-6%, corresponding to approximately 0.5% of the population in northern Sweden. A substantial proportion of those with severe asthma had uncontrolled disease, and severe asthma differed significantly from other asthma in terms of both clinical and inflammatory characteristics.