An outbreak of Acinetobacter baumannii:: The importance of cross-transmission

OBJECTIVE: To investigate an outbreak of nosocomial infections due to multidrug-resistant (MDR) Acinetobacter baumannii and to analyze the contribution of cross-transmission in the rise in infection rates. DESIGN: Epidemiological investigation; molecular typing using pulsed-field gel electrophoresis (PFGE); matched case-control study to identify risk factors for infection. SETTING: A 34-bed surgical intensive care unit at a tertiary-care hospital. PATIENTS: Eighteen patients who developed MDR A baumannii nosocomial infection were matched to 36 patients who were admitted to the same surgical intensive care unit (SICU) room and did not develop an infection during the outbreak period. RESULTS: Prior to the outbreak, the baseline attack rate of MDR A baumannii nosocomial infections was 3 per 100 patients per month. From February 1 through March 22, 1998, the attack rate rose to 16 per 100 patients per month, with a total of 18 infections. All isolates had indistinguishable PFGE patterns. Seventy environmental cultures were negative for MDR A baumannii. Following intense infection control education, the attack rate decreased to 4 per 100 patients per month. By conditional logistic regression, cases were exposed to a significantly higher number of patients with MDR A baumannii infections compared to controls (odds ratio, 1.1; 95% confidence interval, 1.01-1.2; P=.02), even after adjusting for length of SICU admission and exposure to antibiotics and invasive devices. CONCLUSION: Cross-transmission between patients contributed to the rise in rates of MDR A baumannii infections. A common environmental source was not detected.