Respiratory mortality among subjects with a combination of chronic airway diseases: asthma, bronchiectasis, and chronic obstructive pulmonary disease in South Korea

<bold>Introduction:</bold> Little has been reported on respiratory mortality in subjects with a combination of the chronic airway diseases: asthma, bronchiectasis, and chronic obstructive pulmonary disease (COPD). <bold>Methods:</bold> This retrospective cohort study utilized the Korean National Health Insurance Service-National Sample Cohort, representing 2.2% of the Korean population. Subjects newly diagnosed with any chronic airway diseases from 2006 to 2007 were included and followed up until 2019. Cox proportional hazard analysis was performed to obtain the hazard ratio for respiratory death, adjusting for age, sex, Charlson Comorbidity Index, residence region, and household income. <bold>Results:</bold> Among 703,804 subjects, 677,446 (96.3%) did not have any chronic airway diseases. In total, 18,616 (2.7%) had only asthma (A), 2,054 (0.3%) had only bronchiectasis (B), and 3,952 (0.6%) had only COPD (C). Additionally, 310 (0.04%) had A & B, 1,135 (0.2%) had A & C, and 209 (0.03%) had B & C. A small subset of 82 (0.01%) had A & B & C. When compared to subjects without any of the chronic airway diseases, the adjusted hazard ratios of respiratory death were 1.25 (95% confidence interval: 1.08–1.43) for A only, 1.78 (1.35–2.34) for B only, 1.91 (1.67–2.19) for C only, 1.23 (0.58–2.58) for A & B, 2.18 (1.77–2.70) for A & C, 3.89 (2.60–5.82) for B & C, and 5.73 (3.68–8.93) for A & B & C. <bold>Conclusion:</bold> The respiratory mortality appears to be the highest in subjects with COPD, and the second highest in bronchiectasis and the lowest in asthma. In addition, if a subject has a combination of asthma, bronchiectasis, and COPD, the respiratory mortality might be increased.