Correlations between Microbiological Outcomes and Clinical Responses in Patients with Severe Pneumonia

BACKGROUND: In treatment of pneumonia, microorganisms sometimes persist, appear or reappear despite good clinical responses. On the other hand, recent increasing antibiotic resistance emphases the goal of rapid eradication of pathogen in severe infection. This study was planned to evaluate the correlations between microbiological outcomes and clinical responses in severe pneumonia. MATERIALS AND METHODS: Data was gathered from 3 clinical trials regarding severe pneumonia. Microbiological outcomes, determined by serial culture of respiratory tract samples,were compared with clinical outcomes. RESULTS: In total, 146 bacterial strains from 76 patients were analyzed. While clinical success was generally related to total or partial eradication of isolated organisms, Acinetobacter, Enterobacter, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia were often not eradicated and yet were observed in 56% of cases considered clinically successful at the end of antibiotic treatment. Most of the non-eradicated strains (71%) already had or developed resistance against the antibiotics used for treatment. Ten patients relapsed during the follow-up period; 7 of these relapses were associated with 10 non-eradicated organisms. CONCLUSIONS: These data raise concern about the pathogenicity of bacteria that persist in the respiratory tract even though good clinical outcomes of pneumonia are achieved, especially when Acinetobacter, Enterobacter, P. aeruginosa, or S. maltophilia were involved. Thus, clinical relapse and development of drug resistance by non-eradicated organisms may be raised.