Emergence of multidrug-resistant isolates of Acinetobacter baumannii

Patterns of antimicrobial resistance during an outbreak of nosocomial infections caused by Acinetobacter baumannii were studied. The medical records of all patients admitted to the hospital between February 1993 and February 1994 from whom A. baumannii was cultured were reviewed for demographic data, confirmation of the isolation report, admission date, date of first isolation of the organism, and antimicrobial use before and after the culture and susceptibility test results were obtained. The culture and susceptibility test data were reviewed for all specimens submitted to the laboratory during the review period. A total of 87 patients (mean +/- S.D. age, 37.9 +/- 8.7 years) with nosocomial infection or colonization with A. baumannii were identified. All the patients were surgical intensive care unit residents and had predisposing factors for acinetobacter infection. A total of 107 isolates of the organism were cultured from various sites; sputum was the most common source. The number of isolates per month increased steadily beginning in September 1993 and then declined over the winter. The median time between admission and first isolation of resistant A. baumannii was 11 days. Infections were manifested clinically as pneumonia (36 patients), bacteremia (8), wound infection (6), and urinary-tract infection (2). Of the 107 isolates, all were resistant to formulary cephalosporins, extended-spectrum penicillins, quinolones, and aztreonam. Only nine isolates were susceptible to one or more aminoglycosides. All the isolates were susceptible to imipenem-cilastatin. During an outbreak of nosocomial infections with A. baumannii, all or nearly all of the 107 isolates were resistant to a broad range of antimicrobials with the exception of imipenem-cilastatin, to which all the isolates were susceptible.