Key Point:

Some COPD patients appear to have persistent colonization with H influenzae, which could affect the frequency and severity of exacerbations.

erial cause. However, if the patient is colonized with a pathogen at levels undetectable to a sputum culture, a greater proportion of COPD exacerbations may have an underlying bacterial cause.

If this is true, said Dr. Murphy, who is also Chief of the Infectious Diseases Division at Buffalo Veterans Affairs Medical Center, “it would represent a strong rationale to attempt to eradicate colonization, for example, with vaccines, antiadhesive agents, cycling of antibiotics, or other novel approaches.”

EXPLAINING PERSISTENCE

“The mechanism of persistence is of great interest,” observed Dr. Murphy, and has opened the way for two lines of investigation. “One is that H influenzae forms biofilms in the respiratory tract. Biofilms are an altered form of bacterial growth in which bacteria adhere to a surface and are encased within a matrix. Bacteria in biofilms are more difficult for the immune system to eradicate and more resistant to antibiotics,” he said.

A second potential mechanism, according to Dr. Murphy, is that H influenzae enters cells. “The organism is known to be able to survive intracellularly,” he pointed out. “In this way it may ‘hide’ from antibodies and antibiotics, allowing it to persist in the respiratory tract.”

This study points out the importance of assessing the role played by persistent colonization with H influenzae on respiratory tract infections in COPD patients and raises some interesting questions. For example, the authors asked, does colonization with H influenzae influence the likelihood of colonization by another species or strain? In what ways could colonization affect the incidence of viral infections in these patients?

Dr. Murphy added that although the study team also isolated Moraxella catarrhalis and Streptococcus pneumoniae from sputum cultures, persistent colonization seemed to be characteristic only of H influenzae.

—Gale Jurasek

Reference
1. Murphy TF, Brauer AL, Schiffmacher AT, Sethi S. Persistent colonization by Haemophilus influenzae in chronic obstructive pulmonary disease. Am J Respir Crit Care Med. 2004;170:266-272.

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