Rationale: Moraxella catarrhalis is frequently present in the sputum of adults with chronic obstructive pulmonary disease (COPD). Little is known about the role of M. catarrhalis in this common disease.
Objective: To elucidate the burden of disease, the dynamics of carriage, and immune responses to M. catarrhalis in COPD.
Methods: Prospective cohort study of 104 adults with COPD in an outpatient clinic at the Buffalo Veterans Affairs Medical Center.
Measurements: Clinical information, sputum cultures, molecular typing of isolates, and immunoassays to measure antibodies to M. catarrhalis.
Main results: Over 81 months, 104 patients made 3,009 clinic visits, 560 during exacerbations. Molecular typing identified 120 episodes of acquisition and clearance of M. catarrhalis in 50 patients; 57 (47.5%) of the acquisitions were associated with clinical exacerbations. No instances of simultaneous acquisition of a new strain of another pathogen were observed. The duration of carriage of M. catarrhalis was shorter with exacerbations compared with asymptomatic colonization (median, 31.0 vs. 40.4 days; p = 0.01). Reacquisition of the same strain was rare. The intensity of the serum IgG response was greater after exacerbations than asymptomatic colonization (p = 0.009). Asymptomatic colonization was associated with a greater frequency of a sputum IgA response than exacerbation (p = 0.009).
Conclusions: M. catarrhalis likely causes approximately 10% of exacerbations of COPD, accounting for approximately 2 to 4 million episodes annually. The organism is cleared efficiently after a short duration of carriage. Patients develop strain-specific protection after clearance of M. catarrhalis from the respiratory tract.