Understanding Serratia bockelmannii transmission during a neonatal intensive care unit outbreak: a combined genotyping and case-control study.

BACKGROUND

Serratia marcescens complex (SMC) is a group of opportunistic pathogens frequent in neonatal intensive care unit (NICU) outbreaks. We report a seven-month NICU outbreak of multidrug-resistant (MDR) SMC strain and assess the acquisition risk factors.

METHODS

Bacterial isolates were sequenced using Illumina technology and profiled for antimicrobial resistance (AMR). Cases (culture positive for SMC) were compared with birth date and ward-matched controls (SMC negative) to identify clinical and environmental factors associated with SMC acquisition.

RESULTS

A single strain of Serratia bockelmannii caused 42 cases from June 2022 to January 2023. All sequenced isolates (n = 49) carrued the same AMR genes, while the antibiogram (n = 32) assigned 15 strains as MDR, and 17 as non-MDR. The outbreak strain was recovered from ward surfaces and an analytical study revealed that beds used by several cases increased the acquisition odds by 3.27 (95%CI 1.71-8.77, p-value = 0.003) after adjusting for sex and length of stay.

CONCLUSIONS

The genomic typing was pivotal in confirming clonality across S. bockelmannii isolates with varied antibiograms, and identifying the bacterial species. Serratia bockelmannii should be considered during SMC outbreaks. Incubator-related within-ward transmission highlights the need for tailored risk assessments and disinfection protocols to prevent pathogen transmission and to improve infection prevention protocols.