Risk factors of asthma exacerbation based on asthma severity: a nationwide population-based observational study in South Korea

Objectives Asthma exacerbation, associated with many risks factors, can reflect management failure. However, little is known about how risk factors are associated with exacerbation, according to asthma severity. We aimed to investigate differences in risk factors in patients with different asthma severity and evaluate whether risk factors differed between frequent exacerbators and patients with single exacerbation. Design Nationwide population-based observational study. Setting Korean National Sample Cohort database. Participants We included 22130 adults with asthma diagnoses more than twice (ICD-10 (International Classification of Diseases, Tenth revision) codes J45 and J46) and one prescription for asthma medication from 2010 to 2011. Outcome measures Asthma exacerbation was defined as having a corticosteroid (CS) burst characterised by a prescription of high-dose oral CS for >= 3 days or one systemic CS injection, hospitalisation or emergency department visit. Results Among severities, history of CS bursts was significantly associated with exacerbation. In mild and moderate asthma, exacerbation was significantly associated with age >= 45 years, being female, gastrooesophageal reflux disease and chronic rhinitis. High medication possession ratio (MPR >= 50%), compared with low MPR (<20%) showed adjusted ORs of 0.828 (95% CI 0.707 to 0.971) and 0.362 (0.185 to 0.708) in moderate and severe asthma, respectively. In severe asthma, compared with mild asthma, only allergic rhinitis and history of hospitalisation were strongly associated with exacerbation. When comparing frequent exacerbators to patients with single exacerbation, age >= 45 years, atopic dermatitis, anxiety and history of CS burst were significant risk factors in mild and moderate asthma, whereas no risk factors were significant in severe asthma. Conclusions Different associations between risk factors and asthma exacerbations based on asthma severity suggest that patients with mild asthma require greater attention to their age and comorbidities, whereas those with severe asthma require greater attention to hospitalisation history and drug adherence.