Background. Most literature regarding lung abscess focuses on anaerobic bacterial lung abscess, and aerobic gram-negative bacillary infection is less frequently discussed. This study was conducted to investigate the bacteriology of community-acquired lung abscess and to improve the empirical therapeutic strategy for adults with community-acquired lung abscess. Methods. We reviewed and analyzed data on 90 consecutive adult cases of bacteriologically confirmed community-acquired lung abscess treated during 1995-2003 at a tertiary university hospital in Taiwan. Results. We found that a high proportion (21%) of cases of lung abscess were due to Klebsiella pneumoniae infection, which differs from the findings of previous studies. Lung abscess due to K. pneumoniae was associated with underlying diabetes mellitus (odds ratio [OR], 4.3; 95% confidence interval [CI], 1.0-18.4; P = .039) and negatively correlated with a time from onset of symptoms to diagnosis of >30 days (OR, 0.2; 95% CI, 0.1-0.7; P = .008). A higher percentage of patients with K. pneumoniae lung abscess had concomitant bacteremia (OR, 9.4; 95% CI, 1.1-81.9; P = .032), delayed defervesence (OR, 9.2; 95% CI, 1.8-47.8; P = .004), and multiple cavities noted on radiographs (OR, 11.0; 95% CI, 1.3-94.9; P = .015), compared with patients with anaerobic bacterial lung abscess. The rate of nonsusceptibility to clindamycin and penicillin among anaerobes and Streptococcus milleri group isolates increased. Conclusion. K. pneumoniae has become a more common cause of lung abscess than before, and a high proportion of anaerobes and S. milleri strains have become resistant to penicillin and clindamycin. A β-lactam/ β-lactamase inhibitor or second- or third-generation cephalosporin with clindamycin or metronidazole is suggested as empirical antibiotic therapy for community-acquired lung abscess.
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