© 2005 American Thoracic Society
Are Colonial Haemophilus influenzae Responsible for Exacerbations of Chronic Obstructive Pulmonary Disease After All?From the Authors:The more we learn more about the dynamics of colonization and infection of the respiratory tract in adults with chronic obstructive pulmonary disease (COPD) by Haemophilus influenzae, the more complex the story becomes. When a new strain acquisition of H. influenzae occurs, multiple outcomes are possible, including the presence or absence of clinical symptoms of exacerbation (1), the presence or absence of mucosal and systemic antibody responses (2), the presence or absence of T-cell responses (3), rapid clearance of the organism, persistent colonization (4, 5), and combinations of these scenarios. Indeed, the process of new strain acquisition and persistent colonization coexist in these patients. Our prospective data indicate that a primary mechanism of bacterial exacerbation is acquisition of a new strain (1). Our current study (4) establishes that patients may be persistently colonized by H. influenzae despite negative sputum cultures. Thus, we agree with Dr. Lee and colleagues that studies which rely on sputum cultures to indicate absence of H. influenzae must be interpreted with caution. The interesting observations of Bresser and colleagues (6) are derived from a selected group of 19 patients who were heavily colonized by H. influenzae. The frequency of positive cultures for H. influenzae in their patients was 74%, whereas the frequency of positive cultures for H. influenzae in our unselected patients with COPD was 21%. We observed a similar subgroup of patients with high levels of colonization and infection within our study population as well. These observations emphasize the heterogeneity of patients with COPD with regard to the role of bacteria in the disease. We fully agree with Dr. Lee and colleagues that the result of a sputum culture alone does not reliably identify the etiology of an exacerbation. However, the reality is that a negative sputum culture would cause most clinicians to conclude that the exacerbation was not bacterial in etiology. The observation that H. influenzae persistently colonizes the respiratory tract has important implications beyond a consideration of the etiology of exacerbations. It will be most interesting to assess the effect of persistent colonization on airway inflammation, on daily symptoms of COPD, and on the susceptibility of superimposed infection by viruses and other bacteria. Such studies will help to elucidate more subtle but potentially important effects of H. influenzae colonization on the course and pathogenesis of COPD.
University at Buffalo, State University of New York Buffalo, New York FOOTNOTES Conflict of Interest Statement: T.F.M. does not have a financial relationship with a commercial entity that has an interest in the subject of this letter; S.S. does not have a financial relationship with a commercial entity that has an interest in the subject of this letter. REFERENCES
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