Chest
Volume 118, Issue 1, July 2000, Pages 193-203
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Debate in Print
Do Bacteria Cause Exacerbations of COPD?

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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.

Section snippets

Microbiological Studies

Protected brush samples obtained from the lower respiratory tract by bronchoscopy in both hospitalized and ambulatory patients with exacerbations yield significant growth of potential bacterial pathogens in only about 50% of specimens.7, 20, 21 In these studies S pneumoniae and H influenzae, alone or together, constitute a large proportion of the isolates, being present in about 30 to 40% of all the patients. Most investigations using cultures of expectorated sputum have also identified these

Serologic Studies

Several studies have examined the immunologic response associated with exacerbations. One investigation employed a RBC agglutination technique with an antigen obtained from a fresh isolate of H influenzae.36 Antibody titers did not rise during exacerbations, even when H influenzae grew from the sputum. Another study employed a complement fixation test using a soluble antigen prepared from a single strain of unencapsulated H influenzae.37 In a small group of patients with COPD studied during

Placebo-Controlled Studies

An ideal study of antibiotic efficacy in exacerbations should be prospective, randomized, double-blind, and placebo-controlled. It should enroll numerous patients to ensure a representative population sample and to avoid missing an effect because of inadequate numbers of participants. Using chest radiographs, it should exempt patients with parenchymal opacities consistent with pneumonia, since the inclusion of participants with that infection would, of course, favor antibiotics. The trial

Conclusion

Assessing the available studies with the criteria delineated earlier fails to provide compelling evidence that bacteria cause COPD exacerbations:

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