Methods

Study population

The study sample was derived from the ongoing West Sweden Asthma Study (WSAS), a longitudinal cohort study investigating different aspects of airway diseases among a representative sample of adults of western Sweden. WSAS started in 2008 in which a random sample of 30,000 individuals aged 16-75 years were invited to participate in a postal survey. Of those who responded to the questionnaire, 2,000 randomly selected subjects and 1,524 individuals with self-reported asthma were further invited to undergo detailed clinical investigations, conducted between 2009 and 2012 (WSAS I). A total of 2,006 subjects participated in this initial clinical examination. In 2016, a non-overlapping sample from western Sweden was added to WSAS, using the same survey and clinical investigation methods. Put together, a total of 3,101 individuals underwent clinical investigations before the start of COVID-19, at which time clinical data collection was put on hold due to the pandemic, of which 1,895 subjects who had ever had asthma were included in the current phenotyping work. A detailed description of the WSAS cohort design and characteristics has been reported previously9.

Assessment and measurements