Genomic epidemiologic assessment implicates prolonged silent carriage, virulence factors and transmission between staff and patients in a NICU outbreak of MRSA

Abstract

ABSTRACTIntroductionMethicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen in neonatal intensive care units (NICU) that carries significant morbidity and mortality. Improving our understanding of MRSA transmission dynamics, especially among high risk patients, is an infection prevention priority.MethodsWe investigated a cluster of clinical MRSA cases in the NICU using a combination of epidemiologic review and whole genome sequencing (WGS) of isolates from clinical and surveillance cultures obtained from patients and healthcare personnel (HCP).ResultsPhylogenetic analysis identified two genetically distinct phylogenetic clades and revealed multiple silent transmission events between HCP and infants. The predominant outbreak strain harbored multiple virulence factors. Epidemiologic investigation and genomic analysis identified a HCP colonized with the dominant MRSA outbreak strain who cared for the majority of NICU patients who were infected or colonized with the same strain, including one NICU patient with severe infection seven months before the described outbreak. These results guided implementation of infection prevention interventions that prevented further transmission events.ConclusionSilent transmission of MRSA between HCP and NICU patients likely contributed to a NICU outbreak involving a virulent MRSA strain. WGS enabled data-driven decision making to inform implementation of infection control policies that mitigated the outbreak. Prospective WGS coupled with epidemiologic analysis can be used to detect transmission events and prompt early implementation of control strategies.SummaryWhole genome sequencing identified a NICU outbreak of MRSA preceded by silent transmission between health care personnel and patients seven months prior to outbreak detection. This study suggests prospective genomic analysis may identify isolates with high virulence potential, offering an early opportunity for intervention.