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

Background: Serratia marcescens is an aerobic Gram-negative Enterobacterales bacillus that has emerged as a cause of hospital-associated infections.

Aim: To report the epidemiological, diagnostic, and genetic investigation of an outbreak involving five neonatal patients infected or colonized with S. marcescens including the infection control interventions.

Methods: The outbreak occurred in a 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. In-flight patients and their immediate environment were screened for S. marcescens to determine probable environmental sources. Whole-genome sequencing (WGS) analysis of resulting isolates was performed 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.

Findings: Five neonates infected or colonized with S. marcescens were involved in this outbreak. Four were infection cases and one was 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: A multi-prong strategy was required to contain this outbreak. WGS analysis showed association of biofilms in sinks with the outbreak.