[Infectious comorbidity in COPD]

Respiratory infection is the most frequent and characteristic infectious comorbidity in patients with chronic obstructive pulmonary disease (COPD) and can lead to two clinical scenarios. The first and most common is exacerbation, although not all exacerbations are caused by infections, which account for 50-70% of these processes. The second scenario is pneumonia, since COPD is the most frequent comorbidity associated with the development of pneumonia. Of the infectious agents causing exacerbations, 50-60% of cases correspond to bacteria, which are the most widely studied microorganisms and whose role is becoming increasingly notorious. Among bacteria, a greater number of Pseudomonas aeruginosa and more aggressive microorganisms are being isolated in exacerbations. A second cause of infectious exacerbations are viruses, which seem to play an important role in these processes, although less so than bacteria. Viral infections seem to predispose many patients to a subsequent bacterial infection. Community-acquired pneumonia (CAP) is highly common in patients with COPD and between 25 and 50% of patients hospitalized with this diagnosis have COPD. Nevertheless, COPD has not been considered as a risk factor for poor outcome in patients with CAP and the Pneumonia Severity Index (PSI) showed that COPD was not among the comorbidities associated with mortality at 30 days. Although some studies have recently associated COPD with increased mortality, this association is questionable and the possible improved outcome could be due to the use of systemic corticosteroids in most patients with COPD.