Understanding and controlling an MRSA outbreak using whole genome sequencing

Abstract

The emergence of meticillin-resistant Staphylococcus aureus (MRSA) that can persist in the community and replace existing hospital-adapted lineages of MRSA means that it is necessary to understand transmission dynamics within and between hospitals and the community. We studied a putative MRSA outbreak on a special care baby unit (SCBU) at Addenbrooke's Hospital, Cambridge, UK. We used whole-genome sequencing to assess and improve-upon the findings of an infection-control team who evaluated the outbreak with conventional epidemiological analysis and antibiogram profiles. We sequenced isolates from all colonised infants on the SCBU, and from patients in the hospital or community who had presented with MRSA with the same antibiotic susceptibility profile as the outbreak strain. The original infection control team identified 12 cases of MRSA infection in infants over a 12-month period which were suspected of being linked. However, a persistant outbreak could not be confirmed. Using whole-genome sequencing we identified 26 related cases of MRSA carriage and showed transmission occurred within the SCBU, between mothers on a postnatal ward, and in the community. Based on our results, we also proposed that MRSA carriage by a staff member had allowed the outbreak to persist during a period without known infection on the SCBU and after a deep clean. Staff screening led to identification and decolonisation of a staff carrier, which brought the outbreak on the ward to a close. Whole-genome sequencing holds great promise for rapid, accurate, and comprehensive identification of bacterial transmission pathways both within hospitals and in the community, and its widespread use in the clinical setting will bring reductions in infections, morbidity, and costs.