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Chronic airway obstruction in a population-based adult asthma cohort: prevalence, incidence and prognostic factors

Helena Backman, Sven-Arne Jansson, Caroline Stridsman, et al.
Respir Med 2018;138:115–22

People with asthma may develop chronic airway obstruction (CAO). Its prevalence in patients recruited from hospitals and primary care ranges from 29% to 60%, and from 19% to 32% in population-based samples. The incidence of CAO has not been recorded, and risk factor patterns for prevalent CAO among asthmatics are conflicting. Asthma-COPD overlap (ACO), proposed by joint Global Initiative for Asthma and GOLD guidelines, lacks an accepted definition, and it is unclear whether the term is a distinct disease entity or used to describe the co-existence of both asthma and COPD. Whichever it may be, it is important to study the natural history of ACO, so as to better define management and treatment of those affected.

The aims of this study were to estimate prevalence and incidence of CAO in a large population-based adult asthma cohort, and to study risk factors for both prevalent and incident CAO. The asthma cohort comprised 2,055 adults aged 19–72 years, and the study was run between 1986 and 2001. CAO was defined as post-bronchodilator FEV1/FVC<0.7. The cohort was invited to a clinical follow-up involving interview, spirometry and blood sampling in 2012–2014, of whom 983 attended.

The study concluded that the prevalence of CAO at study entry level was 11.4%. The incidence rate was 16 per 1,000 per year, meaning the majority did not develop CAO. Those with CAO had higher levels of neutrophils and greater incidence of heart disease. Risk pattern factors for both prevalent and incident CAO were similar, and corresponded to that of general population COPD patients, namely, smoking, older ages and male sex. There was nothing in the findings to suggest ACO is a specific disease entity.

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