Serratia marcescens outbreak at a neonatal intensive care unit in an acute care tertiary hospital in Singapore.

Objective: To report the epidemiological, diagnostic, and genetic investigation of an outbreak of neonatal patients infected or colonized with Serratia marcescens (S. marcescens) including the infection control interventions.

Design: Outbreak investigation report.

Setting: 28-bedded neonatal unit in an acute care tertiary hospital in Singapore divided into three areas: two negative-pressure airborne infection isolation rooms with a shared anteroom, 10 neonatal intensive care unit (NICU) beds, and 16 high dependency beds.

Patients: A total of five neonates were involved in this outbreak.

Methods: Screening of in-flight patients and their immediate environment for S. marcescens to determine probable environmental sources, whole genome sequencing (WGS) analysis of resulting isolates to determine clone-relatedness and possible transmission patterns. Implementation of infection control interventions included prompt isolation of cases, enhanced equipment and environmental disinfection, use of alcohol-based hand rub as the preferred hand hygiene mode, enhanced infection prevention orientation for parents, review of practices, audits, and immediate feedback on non-compliance.

Results: Five neonates infected or colonized with S. marcescens were involved in this outbreak. Four were infection cases whilst one identified through contact tracing. Three NICU sinks and the milk preparation room sink were tested positive for S. marcescens. WGS confirmed clonality of strains from two NICU sinks, and milk preparation room sink with that of the five neonates.

Conclusion: Multiprong strategy was required to contain this outbreak. WGS analysis showed association of biofilms in sinks with the outbreak.