Serratia marcescens outbreak in a neonatal intensive care unit and the potential of whole-genome sequencing

BACKGROUND: Serratia marcescens is notorious for its increasing antimicrobial resistance and potential to cause outbreaks in neonatal intensive care units (NICU). A promising tool in outbreak investigation is whole-genome sequencing (WGS).

OBJECTIVES: To describe a S. marcescens outbreak (2018-2019) on a NICU and discuss which infection control measures contributed to the containment, addressing the potential of WGS.

MATERIALS AND METHODS: S. marcescens isolates from NICU patients and the environment isolated during the 2018-2019 outbreak were analyzed. In comparison, isolates from previous presumed NICU outbreaks, and adult blood cultures were included. WGS and whole-genome multilocus sequence typing analysis were performed.

RESULTS: Sixty-three S. marcescens isolates were analyzed. The 2018-2019 outbreak was divided in three clusters, including four environmental strains (drains, n=3; baby scale, n=1). The strains differed significantly from those of a NICU outbreak in 2014 and adult blood cultures. Besides standard infection control measures, the siphons were replaced, and weekly decontaminated with acetic acid (10%). Seven acquired resistance, and 29 virulence-associated genes could be detected.

CONCLUSIONS: We assume that both, neonates and drains, were reservoirs of S. marcescens cross-contamination through hands. We started with reinforcement of standard measures, including hand hygiene. However, definitive containment was achieved only after replacement of the siphons and weekly decontamination with acetic acid. Based on WGS, more rapid recognition of an outbreak with accurate mapping of the spread is possible, facilitating the implementation of infection control measures. Furthermore, interesting information about (the spread of) antibiotic resistance and virulence genes is easily provided.