Acinetobacter baumannii outbreak in an intensive care unit (ICU): Epidemiologic investigation and resolution

Abstract

BACKGROUND/OBJECTIVES: According to recent literature, Acinetobacter baumannii (Ab) ranks second after Pseudomonas in causing healthcare-associated gram-negative infections. Historically, pathogen prevalence monitoring for our 19-bed ICU revealed 0-1 Ab isolates per month. Between February 10 and 19, 2004, a cluster of five multidrug-resistant Ab (MDR Ab) positive sputum cultures from the ICU prompted an investigation. METHODS: Routine epidemiologic surveillance includes daily review of culture reports and quarterly cumulative pathogen prevalence reporting for the ICU. This investigation included a line listing of cases with a timeline, molecular study of isolates by pulsed-field gel electrophoresis (PFGE), direct observations of patient care practices, and communication of findings to ICU staff. RESULTS: All five patients were Ab culture-negative upon admission to the ICU; all MDR Ab antibiotic sensitivity data were similar or identical. PFGE showed isolates to be very similar and considered identical given the epidemiologic link. All stays in the ICU overlapped chronologically, and compliance with established isolation and hand hygiene practices was observed to be inconsistent. Repeated verbal reinforcement of hand hygiene and isolation policies improved adherence to infection control policies. The prevalence of Ab in the ICU returned to historical baseline in March 2004. During the investigation, one MDR Ab isolate from the ICU (January 1, 2004) thought unrelated to the outbreak was included as a control. This isolate had the same dendogram as the outbreak isolates. Additional investigation revealed that this patient had been in the ICU at the same time as one of the February outbreak patients and provided the epidemiologic link identifying this January 1 patient as the “index case.” The investigation was expanded to include January. Two additional patients had MDR Ab positive cultures (January 4 and January 27), thus increasing the number of outbreak cases to eight. CONCLUSIONS: Pathogen prevalence surveillance combined with daily review of culture reports is effective to identify an outbreak in a timely manner and optimizes the ability to intervene. Immediately sharing the molecular study results and timeline of patient stays with the ICU staff helped them understand the outbreak and accept responsibility for infection prevention. Improved adherence to hand hygiene and isolation techniques resolved this outbreak.