Investigation of an outbreak of Serratia marcescens in a neonatal intensive care unit

Abstract

Serratia marcescens is a well-known but relatively uncommon cause of nosocomial infections, particularly in neonatal intensive care unit (NICU) patients. We investigated an outbreak of S marcescens in the NICU at the Farabi Hospital of Karadeniz Technical University in Trabzon, Turkey. Between March 21 and May 27, 2006, nine of the neonates were identified with cultures of S marcescens, and there were three deaths because of septicemia. For the purpose of identifying the source of infection, 85 environmental samples, two breast milk samples from two babies' mothers, and 38 hand-washing samples from the health care workers (HCWs) were collected for the detection of S marcescens. All the S marcescens isolates were genotyped by pulsed-field gel electrophoresis with endonuclease SpeI restriction enzyme. Serratia marcescens was identified from one hand-washing sample and two breast milk samples. None of the environmental samples yielded S marcescens. Of the 13 isolates analyzed, four belonged to one major genotype, whereas eight (6 from neonates and 2 from breast milk) were indistinguishable; two isolates (2 from neonates) were closely related; and three isolates (2 other neonates and 1 from HCW's hand) were different. Our intensive efforts failed to determine the source of the outbreak despite the finding that S marcescens strain was isolated from a HCW's hand. Present investigation suggested that an outbreak of S marcescens infection was caused by a major clone in our NICU, possibly transmitted through the hands of HCWs, emphasizing that strict hand washing before and after contact with patients must be the rule of the thumb.