The outcome of community-acquired pneumonia in patients with chronic lung disease: a case-control study

The impact of chronic lung diseases on outcome in community-acquired pneumonia (CAP) is not well established. We aimed to investigate the outcome of adult CAP-patients with underlying chronic obstructive pulmonary disease (COPD), asthma or interstitial lung disease (ILD) in a case-control study.

We used a nationwide database including all hospitalisations in Switzerland from 2002 to 2010. Endpoints were the incidence of lung abscess, parapneumonic pleural effusion, empyema, acute respiratory distress syndrome, in-hospital mortality and length of stay.

We found less disease-related complications of CAP in COPD (n = 17,075) and asthma (n = 2700) patients compared with their controls. This difference was mainly related to a lower incidence of pleural effusion (COPD: 4.3% vs 4.9%, p = 0.011; asthma: 3.4% vs 5.2%, p <0.001). In-hospital mortality was lower in the COPD and - much more pronounced - asthma cohorts (COPD: 5.8% vs 6.7%, p <0.001; asthma: 1.4% vs 4.8%, p <0.001). For ILD (n = 916), the complication rate was similar as compared to the control group, whereas in-hospital mortality was markedly higher (16.3% vs 6.8%, p <0.001).

These rather unexpected results should be viewed as hypothesis generating, with various possible explanations for our findings. These include the possible influence of inhaled corticosteroid therapy, a possibly higher awareness of general practitioners and hospital physicians while treating patients with chronic lung diseases, a different infective agent spectrum or a different immune response.