Investigation and control of a Meticillin-resistant Staphylococcus aureus (MRSA) outbreak in a Level 2 neonatal unit in England - Findings from a cohort study.

Neonatal unit outbreaks of Meticillin-resistant Staphylococcus aureus (MRSA) can be challenging to control; understanding risk factors for transmission is important. We present findings from a neonatal unit MRSA colonization outbreak investigation, detected through routine screening. To describe the outbreak investigations, and risk factors identified through a cohort study. Cases were neonatal unit inpatients from May to September 2023 with an MRSA-positive sample within the Whole Genome Sequencing (WGS) linked outbreak cluster. Concurrent screening of mothers was conducted throughout along with one-off staff and environmental sampling. We reviewed hospital record data for all unit inpatients between May-September. A retrospective cohort study was conducted. Of 84 neonatal unit inpatients, 14 (16.7%) had MRSA colonizations within the WGS-linked cluster. There were two outbreak waves: 7 cases in outbreak week 1 to 8, and 7 cases in weeks 16 to 19. Median time between admission and first MRSA-positive swab was 9.5 days (range 3-24). In univariable analysis, MRSA colonization was associated with lower gestational age, lower birth weight, and having clinical exposures (respiratory support, invasive lines and gavage or enteral feeding). No association was identified with staff exposures, twin birth, delivery method or cot exposures. Maternal and environmental screening identified no MRSA-positives. Staff screening identified two outbreak-strain positives. We describe an outbreak of MRSA colonizations in a neonatal unit in England, and the risk factors for infant colonization, identified by conducting a cohort study. The outbreak, whilst complex, was successfully controlled with the second outbreak wave guiding implementation of additional control measures, including staff screening.