Outbreak of gentamicin-resistant Acinetobacter baumanii in an intensive care unit: Clinical, epidemiological and microbiological features

The clinical, epidemiological and microbiological features of an outbreak of infection and colonisation caused by gentamicin-resistant Acinetobacter baumanii (GRAB) in an 18-bed intensive care unit (ICU) of a 680-bed adult teaching hospital are described. A retrospective review of medical, laboratory and infection control records was followed by prospective surveillance. Typing of isolates was performed by restriction enzyme analysis (REA) of chromosomal DNA. The incidence of GRAB in the ICU increased from 1.26 cases per 1000 occupied bed days (OBDs) for January to June 1993, to 6.62 per 1000 OBDs for July to December 1993 (Chi square = 4.8, P < 0.05), confirming the existence of an outbreak. For the two year period, 1993 and 1994, a total of 45 cases of GRAB infection or colonisation was identified. Males and females were equally represented, with an age range of 16-79 years and a mean age of 51 years. Admitting diagnoses varied, with multiple trauma and head injury predominating (ten cases). For 35 of the 45 cases the initial site of GRAB isolation was sputum or other respiratory tract specimen. Specific treatment for GRAB was initiated in 23 patients, however no deaths were directly attributable to GRAB infection. The period of time between admission to the ICU and first isolation of GRAB ranged from three to 70 days with a median of nine days. Overall, ten (11%) of 91 staff hand samples and one of 37 (3%) environmental samples yielded GRAB. All GRAB isolates produced similar biochemical profiles and antibiotic resistance patterns, except for a group of five which were ciprofloxacin resistant. Thirty patient isolates, all ten staff hand isolates and the environmental isolate produced identical REA patterns. The remaining five patient isolates (all ciprofloxacin resistant) which were available for typing produced a different REA pattern. Our study has documented a moderate-sized outbreak of GRAB in an ICU setting. Typing of isolates using REA was useful in delineating outbreak strains. Carriage of GRAB on staff hands was demonstrated as the most likely source of infection. Despite institution of infection control measures GRAB now appears endemic in the ICU.