COPD stage and risk of hospitalization for infectious disease

Background: Respiratory tract infections are a frequent complication of COPD, but little is known about the incidence, association, and risk of infectious diseases related to impaired lung function. Methods: Participants in the Copenhagen City Heart Study had lung function measured at baseline, and were followed for up to 25 years. All hospitalizations due to any infection were identified through registry linkage. Impaired lung function was defined according to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) staging system. Main results: A total of 3,333 infectious disease hospitalizations (IDHs) occurred during 230,653 person-years of follow-up (PY), corresponding to an overall incidence of 145 IDHs (95% confidence interval [CI], 139 to 149) per 10,000 PY. The incidence,increased with GOLD stage, from 131 (95% CL 126 to 136) for normal COPD, to 170 (95% CI, 146 to 193) for mild COPD, to 230 (95% CI, 207 to 253) for moderate COPD, and 394 (95% CI, 330 to 459) for severe/very severe COPD. The trend in risk persisted after the control of background characteristics using Cox proportional hazards analysis (adjusted relative risks: 1.06 [95% CI, 0.92 to 1.23], 1.39 [95% CI, 1.24 to 1.56], and 2.21 [95% CI, 1.84 to 2.64], respectively; p = 0.001). In subgroup analysis, the increased risk was associated with lower and upper respiratory tract infections, pyothorax, and tuberculosis, but not with influenza, sepsis, skin infections, urinary tract infections, diarrheal disease, or other infectious diseases. Conclusions: The presence of obstructive lung disease is a significant predictor of IDH caused by respiratory tract infections, but not of hospitalizations due to infections outside the respiratory system.