Study of an outbreak of Enterobacter cloacae sepsis in a neonatal intensive care unit: the application of epidemiologic chromosome profiling by pulsed-field gel electrophoresis.

OBJECTIVE From October 1996 to March 1997, a cluster of 11 cases of neonatal sepsis caused by Enterobacter cloacae with similar antimicrobial susceptibility patterns occurred in a neonatal intensive care unit. This outbreak prompted an investigation. METHOD Twelve isolates obtained from 6 neonatal patients who developed E cloacae sepsis during the outbreak were analyzed. Four E cloacae isolates from 2 preterm neonates without E cloacae infection on the same ward, and 1 isolate from the hands of a nurse, were also examined. No E cloacae were isolated from the environment. Bacterial DNA digested with XbaI or NotI was analyzed with pulsed-field gel electrophoresis. RESULT Three distinct banding patterns were identified by pulsed-field gel electrophoresis. Of the 6 preterm infants with sepsis, strain I was identified in 1, strain II in 2, a mixed infection of strains I and II in 2, and strain III was found in only 1 infant. An isolate from the hands of a nurse was identified as strain II, as were the 4 isolates from the 2 preterm neonates without E cloacae infection. Thus, this outbreak of sepsis was caused by 2 genotypes of E cloacae. CONCLUSION This study demonstrates that pulsed-field gel electrophoresis with restriction enzyme digestion is a valuable tool for genetic characterization of multidrug-resistant E cloacae strains during outbreaks.