Do bacteria cause exacerbations of COPD?

Exacerbations of COPD, which include combinations of dyspnea, cough, wheezing, increased sputum production (and a change in its color to green or yellow), are common. The role of bacterial infection in causing these episodes and the value of antibiotic therapy for them are debated. An assessment of the microbiological studies indicates that conventional bacterial respiratory pathogens, such as Streptococcus pneumoniae and Haemophilus influenzae, are absent in about 50% of attacks. The frequency of isolating these organisms, which often colonize the bronchi of patients in stable condition, does not seem to increase during exacerbations, and their density typically remains unchanged. Serologic studies generally fail to show rises in antibody titers to H influenzae; the only report available demonstrates none to Haemophilus parainfluenzae; and the sole investigation of S pneumoniae is inconclusive. Trials with vaccines against S pneumoniae and H influenzae show no clear benefit in reducing exacerbations. The histologic findings of bronchial biopsies and cytologic studies of sputum show predominantly increased eosinophils, rather than neutrophils, contrary to what is expected with bacterial infections. The randomized, placebo-controlled trials generally show no benefit for antibiotics, but most have studied few patients. A meta-analysis of these demonstrated no clinically significant advantage to antimicrobial therapy. The largest trials suggest that antibiotics confer no advantage for mild episodes; with more severe attacks, in which patients should receive systemic corticosteroids, the addition of antimicrobial therapy is probably not helpful.