Risk of pneumonia in adults with chronic cough: a nationwide cohort study

BACKGROUND: Chronic cough affects approximately 10% of adults and is increasingly recognised as a distinct clinical condition. This symptom has increasingly been associated with significant outcomes such as pneumonia. Nevertheless, few large long-term population-based studies have been conducted. METHODS: This retrospective cohort study was performed using nationwide claims data from the Health Insurance Review and Assessment Service in South Korea from 2013 to 2020. Adult patients who visited outpatient clinics for cough (International Classification of Diseases, 10th Revision: R05) were enrolled. Chronic cough was defined as ≥8 visits or ≥56 days. Patients with pneumonia within 2 years before and 6 months after the index date were excluded. The main outcome was incident pneumonia during the 3 year follow-up period. The association between chronic cough and incident pneumonia was evaluated using Cox proportional hazards models, with HRs adjusted for age, sex, comorbidities and Charlson comorbidity index. Sensitivity analyses and subgroup analyses by sex and age were also performed. RESULTS: Among 385 417 participants (28 706 with chronic cough and 356 711 controls), the incidence of pneumonia was higher in the chronic cough group (18.87 vs 11.32 per 1000 person-years). Chronic cough was independently associated with an elevated risk of pneumonia (adjusted HR 1.13; 95% CI 1.06 to 1.19; p<0.001), and the association was robust across multiple sensitivity analyses with alternative exposures. The subgroup analysis showed a stronger association among men (HR 1.72) than among women (HR 1.39) and among adults aged 40-79 years, with the highest risk observed among adults aged 40-49 years (HR 1.37). CONCLUSIONS: Chronic cough was independently associated with increased pneumonia risk, especially in middle-aged and male patients. Clinicians should be aware that chronic cough may signal increased vulnerability to lower respiratory tract infections (eg, pneumonia) and consider preventive strategies, including vaccination and close monitoring, for high-risk individuals.