Study objective: In patients with severe COPD, acute infective exacerbations are frequent. Streptococcus pneumoniae and Haemophilus influenzae are the most commonly isolated bacteria in sputum cultures from these patients. We hypothesized that in patients with advanced disease, Gram-negative bacteria other than H influenzae play at least an equally important role.
Methods: We evaluated clinical data and sputum culture results from 211 unselected COPD patients admitted to our hospital with an acute infective exacerbation of COPD. One hundred twelve patients fulfilled our protocol criteria of reliable microbiologic results and reproducible lung function tests; the patients were categorized according to the recently published three stages of severity.
Results: Lung function tests revealed an FEV1 of > or =50% of the predicted value in 30 patients (stage I), an FEV1 of 35% to <50% of the predicted value in 30 patients (stage II), and an FEV1 of < or =35% of the predicted value in 34 patients (stage III). Bacteria were classified into three groups: group 1 contained S pneumoniae and other Gram-positive cocci; group 2, H influenzae and Moraxella catarrhalis; and group 3, Enterobacteriaceae and Pseudomonas spp. For all patients together, the most frequently isolated bacteria were group 3 organisms (Enterobacteriaceae and Pseudomonas spp, 48.2%), followed by group 1 organisms (S pneumoniae and other Gram-positive cocci, 30.4%), and group 2 organisms (H influenzae and M catarrhalis, 21.4%). In stage I patients, 14 of 30 had bacteria from group 1, seven of 30 had group 2, and nine of 30 had group 3. In stage II patients, eight of 30 had group 1 bacteria, 10 of 30 had group 2, and 12 of 30 had group 3. In stage III patients, 12 of 52 had group 1 bacteria, seven of 52 had group 2, and 22 of 52 had group 3. The three groups of bacteria causing infective exacerbations were unevenly distributed among the three severity stages of lung function (p=0.016).
Conclusion: There is a correlation between deterioration of lung function and the bacteria isolated from patients with infective exacerbations of COPD. In acute infective exacerbations, Enterobacteriaceae and Pseudomonas spp are the predominant bacteria in patients with an FEV1 < or =35% of the predicted value.