Trends in asthma prevalence among young adults in Denmark – a 20-year nationwide register-based study

Abstract

<b>Background:</b> Knowledge on development in disease prevalence is essential in health care planning, however, recent studies on asthma prevalence have shown inconsistent tendencies according to different populations and methods of investigation. <b>Aim:</b> We sought to investigate the changes in prevalence of active asthma from 1999 to 2018 among young adults in Denmark on a nationwide basis. <b>Methods:</b> By use of Danish national registers, we identified all adults aged 18-45 years as having active asthma if collecting at least two asthma drugs on separate occasions within 12 months since the age of 15 during 1995-2018. The first four years were used as a run-in period. Patients were excluded if registered with a diagnosis for COPD or cystic fibrosis. To minimise the inclusion of remitted asthma, patients were censored after two consecutive years if no verified asthma medication use. <b>Results:</b> The mean annual cohort comprised of 68,807 individuals (SD 1,928) corresponding to an annual prevalence of active asthma of 3.4% among all Danish adults aged 18-45 years (mean annual Danish population of 2,041,478 individuals, SD 39,290). The trend in prevalence was stable from 1999 at 3.2% to 2018 at 3.3%, with only minor fluctuations. The highest prevalence occurred in 2007-2008 at 3.6%. The median age ranged from 33-35 years. Female gender was more frequent, though with a slight decrease from 56% in 1999 to 54% in 2018. <b>Conclusion:</b> While many studies report an increasing trend in asthma prevalence, the annual prevalence of active asthma among young adults in Denmark has been stable during the last 20 years of approximately 3.4% with a slight female predominance.