The Etiology and Antimicrobial Susceptibility Patterns of Microorganisms in Acute Community-Acquired Lung Abscess

¹ From the Respiratory Intensive Care Unit, Groote Schuur Hospital, and the Departments of Medical Microbiology, Red Cross Children's Hospital and Groote Schuur Hospital, and University of Cape Town, South Africa

Objective: To determine the spectrum and antibiotic susceptibility patterns of microorganisms causing acute community-acquired lung abscess.

Design: A prospective survey.

Setting: Medical emergency department and 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 less than 48 h of antibiotic therapy.

Interventions: Microbiologic specimens obtained by percutaneous lung aspiration and with a protected specimen brush via fiberoptic bronchoscopy were submitted for aerobic and anaerobic culture.

Main outcome measures: Identification of all microorganisms, including anaerobes, and determination of antibiotic susceptibility.

Results: A mean of 2.3 bacterial species per patient was isolated, anaerobes alone being isolated in 44% of cases, aerobes alone in 19%, and mixed aerobic and anaerobic isolates in 22%. Aerobic Gram-negative pathogens were uncommon. In seven patients, Mycobacterium tuberculosis was identified; in two it was associated with other bacteria. In four patients, no organisms were isolated. All the nonmycobacterial 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: Community-acquired acute lung abscess is usually caused by multiple anaerobic and less frequently aerobic Gram-positive microorganisms, which should respond to empirical therapy with amoxicillinclavulanate, chloramphenicol, 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 sensitive to conventional antimicrobial therapy and further investigation with percutaneous lung aspiration or bronchoscopy is indicated only when there is lack of early response to therapy or there is the presence of atypical clinical features.

Key Words: anaerobic microorganisms • diagnosis • lung abscess • lung aspirate • microbiology • therapy

Submitted on February 7, 1995
Accepted on May 18, 2007

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