Serratia marcescens outbreak in a neonatal intensive care unit associated with contaminated handwashing sinks

Purpose

This article describes the origin of a S. marcescens outbreak in a neonatal intensive care unit (NICU).

Materials and methods

A retrospective case-control study including 12 S. marcescens-positive and 22 S. marcescens-negative neonates in the NICU was performed to identify the source of the outbreak. S. marcescens isolates were collected during the outbreak and analyzed using whole-genome sequencing (WGS). IQ-Tree software, BEAST2 software package and SCOTTI software were used to construct a phylogenetic tree and a propagation path map.

Results

The index case occurred on February 21st and outbreak ended on March 9th, 2021, affecting a total of 12 neonates (2 with S. marcescens infection and 10 with S. marcescens colonization). Multivariate logistic regression identified that the distance of <0.8 m between the bed unit and the sink (odds ratio [OR], 20.50; 95 % confidence interval [CI], 1.09–384.86), a large number of rotating nurses within a week (OR 2.58, 95 % CI, 1.09–6.11) and use of humidification water in the incubator (OR 189.70, 95 % CI, 2.76–13027.31) were significant increased risk factors for S. marcescens infection or colonization in the outbreak. WGS sifted out a predominant clone between contaminated handwashing sinks and patients, suggesting that cross-transmission was involved in the dissemination of S. marcescens.

Conclusion

Contaminated handwashing sinks can be a communication intermediary of S. marcescens infection or colonization of neonates in the NICU. A distance of <0.8 m between the bed unit and the sink, and a large number of rotating nurses might play important roles in this outbreak. Attention should be paid to sinks contamination and contact transmission to prevent outbreaks.