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New Bacterial Infections Associated with Flare-Ups of COPD

A new study strongly supports long-held suspicions that many exacerbations of chronic obstructive pulmonary disease are caused by new bacterial infections.

It has long been thought that many exacerbations of chronic obstructive pulmonary disease (COPD) are caused by bacterial infections, but proof of this association was lacking in studies performed 25 years ago. In this 56-month, prospective study, investigators took a fresh look at this issue by using molecular typing to identify new strains within a bacterial species in isolates from sputum samples collected from 81 COPD outpatients during monthly clinic visits.

Acute exacerbations were diagnosed in 374 of 1975 clinic visits. Exacerbations were associated with 33% of visits during which new strains were identified; in contrast, exacerbations were diagnosed in 15.4% of visits during which no new strains were found (relative risk, 2.15; P0.001). Exacerbations were significantly associated with acquisition of new strains of Haemophilus influenzae (RR, 1.69), Moraxella catarrhalis (RR, 2.96), and Streptococcus pneumoniae (RR, 1.77).

Comment: This well-designed and carefully performed study shows a clear relation between exacerbations of COPD and onsets of new bacterial infections, even though it cannot provide definitive proof according to Koch's postulates. However, it is reasonable to conclude that many exacerbations are indeed caused by new bacterial infections, justifying the current practice of instituting empiric antimicrobial therapy for acute exacerbations with purulent sputum. This study highlights the hazards of interpreting routine sputum cultures (without molecular typing to identify new strains) from COPD patients experiencing exacerbations. We should also remember that perhaps a third of exacerbations are probably associated with new viral, and not bacterial, infections.

— Neil R. Blacklow, MD

Published in Journal Watch Infectious Diseases September 6, 2002

Citation(s):

Sethi S et al. New strains of bacteria and exacerbations of chronic obstructive pulmonary disease. N Engl J Med 2002 Aug 15; 347:465-71.

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• Medline abstract (Free)

Anthonisen NR. Bacteria and exacerbations of chronic obstructive pulmonary disease. N Engl J Med 2002 Aug 15; 347:526-7.

• Original article (Subscription may be required)
• Medline abstract (Free)