Infection as a comorbidity of COPD.

The normal lung has several defence mechanisms to deal with microorganisms. Lower respiratory infections in the absence of lung disease are therefore relatively infrequent as compared with upper respiratory tract infections in healthy adults. In the setting of chronic obstructive pulmonary disease (COPD), lower respiratory tract infections, both acute and chronic, occur with increased frequency. As these infections contribute considerably to the clinical course of the patient with COPD, they constitute a significant comorbidity in COPD. Recurrent acute infections by bacterial and/or viral pathogens are now clearly linked with the occurrence of exacerbations of COPD. In addition, the occurrence of pneumonia in COPD has received considerable recent attention as it appears to be increased by the use of inhaled corticosteroids. The role of chronic infection in the pathogenesis of COPD is an active area of research with several different types of pathogens potentially implicated. Additionally, COPD patients with HIV infection have a more rapidly progressive decline in lung function than non-HIV-infected patients. Enhanced understanding of the host-pathogen interaction is needed to better prevent and treat respiratory tract infection in COPD.