THE ETIOLOGY AND ANTIMICROBIAL SUSCEPTIBILITY PATTERNS OF MICROORGANISMS IN ACUTE COMMUNITY-ACQUIRED LUNG ABSCESS

Objective: To determine the spectrum and antibiotic susceptibility pat terns of microorganisms causing acute community-acquired lung abscess. Design: A prospective survey. Setting: Medical emergency department a nd wards of a tertiary teaching hospital. Patients: Thirty-four adult patients with both clinical and radiologic features compatible with a diagnosis of acute community-acquired lung abscess who had received le ss than 48 h of antibiotic therapy. Interventions: Microbiologic speci mens obtained by percutaneous lung aspiration and with a protected spe cimen brush via fiberoptic bronchoscopy were submitted for aerobic and anaerobic culture. Main outcome measures: Identification of all micro organisms, including anaerobes, and determination of antibiotic suscep tibility. Results: A mean of 2.3 bacterial species per patient was iso lated, anaerobes alone being isolated in 44% of cases, aerobes alone i n 19%, and mixed aerobic and anaerobic isolates in 22%. Aerobic Gram-n egative pathogens were uncommon. In seven patients, Mycobacterium tube rculosis was identified; in two it was associated with other bacteria. In four patients, no organisms were isolated. All the nonmycobacteria l isolates were susceptible to amoxicillin-clavulanate and in addition the anaerobes were all susceptible to chloramphenicol and almost all to a combination of penicillin and metronidazole. Among the anaerobes, the level of resistance to penicillin, metronidazole, and clindamycin individually was 21%, 12%, and 5%, respectively. Conclusions: Communi ty-acquired acute lung abscess is usually caused by multiple anaerobic and less frequently aerobic Gram-positive microorganisms, which shoul d respond to empirical therapy with amoxicillin-clavulanate, chloramph enicol, or a combination of penicillin and metronidazole. Tuberculosis , which may be indistinguishable from an acute lung abscess, occurred in 21% of patients in our study. Most bacterial pathogens are sensitiv e to conventional antimicrobial therapy and further investigation with percutaneous lung aspiration or bronchoscopy is indicated only when t here is lack of early response to therapy or there is the presence of atypical clinical features.