Risk of CAP in COPD stratified by smoking status: A population-based cohort study in the UK

Abstract

Background: Smoking increases the risk of community-acquired pneumonia (CAP) and is also associated with Chronic Obstructive Pulmonary Disease (COPD) development. Until now, it is unclear whether CAP development in COPD is due to smoking-related increased susceptibility to infections, or due to COPD pathophysiology itself. Objective: To evaluate the association between COPD and CAP by smoking status. Methods: 62.621 patients with COPD and 191.656 control subjects, matched by year of birth, gender and primary care practice, were extracted from the Clinical Practice Research Datalink (CPRD) between 2005 and 2014. Time-varying Cox proportional hazard models were used to estimate the incidence rates and hazard ratios (HRs) for CAP with exposure to COPD vs. matched controls. Analyses were stratified by age, gender and smoking status. Stratified analyses were performed to calculate HRs by smoking status in COPD vs. matched controls and within both subgroups. Results: Incidence rates of CAP in COPD (32.0/1000 person-years) and matched controls (6.8/1000 person-years) increased with age and female gender. The risk of CAP in patients with COPD was higher compared with matched controls (HR 4.2, 95%CI 4.0-4.4). Current smoking COPD patients had comparable CAP risk (HR 0.9, 95%CI 0.8-1.0) than never smoking COPD patients (reference), while current smoking matched controls had a higher risk of CAP (HR 1.2, 95%CI 1.1-1.3) compared to never smoking matched controls. Conclusion: COPD patients have a fourfold increased risk to develop CAP, independent of smoking status. Identification of factors related with the increased risk of CAP in COPD is warranted, in order to improve the management of patients at risk.