Severe asthma-A population study perspective

BackgroundSevere 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. ObjectiveTo describe characteristics and estimate the prevalence of severe asthma in a large adult population-based asthma cohort followed for 10-28years. MethodsN=1006 subjects with asthma participated in a follow-up during 2012-14, when 830 (mean age 59years, 56% women) still had current asthma. Severe asthma was defined according to three internationally well-known criteria: the ATS workshop definition from 2000 used in the US Severe Asthma Research Programme (SARP), the 2014 ATS/ERS Task force definition and the GINA 2017. All subjects with severe asthma according to any of these criteria were undergoing respiratory specialist care and were also contacted by telephone to verify treatment adherence. ResultsThe prevalence of severe asthma according to the three definitions was 3.6% (US SARP), 4.8% (ERS/ATS Taskforce), and 6.1% (GINA) among subjects with current asthma. Although all were using high ICS doses and other maintenance treatment, >90% did not have controlled asthma according to the asthma control test. Severe asthma was related to age >50years, nasal polyposis, impaired lung function, sensitization to aspergillus, and tended to be more common in women. Further, neutrophils in blood significantly discriminated severe asthma from other asthma. Conclusions and Clinical RelevanceSevere asthma differed significantly from other asthma in terms of demographic, clinical and inflammatory characteristics, results suggesting possibilities for improved treatment regimens of severe asthma. The prevalence of severe asthma in this asthma cohort was 4%-6%, corresponding to approximately 0.5% of the general population.