Whole-genome sequencing data-based modeling for the investigation of an outbreak of community-associated methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit in Hong Kong.

We describe a nosocomial outbreak of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) ST59-SCCmec type V in a neonatal intensive care unit (NICU) in Hong Kong. In-depth epidemiological analysis was performed by whole-genome sequencing (WGS) of the CA-MRSA isolates collected from patients and environment during weekly surveillance and healthcare workers from the later phase of the outbreak. Case-control analysis was performed to analyze potential risk factors for the outbreak. The outbreak occurred from September 2017 to February 2018 involving 15 neonates and one healthcare worker. WGS analysis revealed complicated transmission dynamics between patients, healthcare worker, and environment, from an unrecognized source introduced into the NICU within 6 months before the outbreak. In addition to enforcement of directly observed hand hygiene, environmental disinfection, cohort nursing of colonized and infected patients, together with contact tracing for secondary patients, medical, nursing, and supporting staff were segregated where one team would care for CA-MRSA-confirmed/CA-MRSA-exposed patients and the other for newly admitted patients in the NICU only. Case-control analysis revealed use of cephalosporins [odds ratio 49.84 (3.10-801.46), p = 0.006] and length of hospitalization [odds ratio 1.02 (1.00-1.04), p = 0.013] as significant risk factors for nosocomial acquisition of CA-MRSA in NICU using multivariate analysis. WGS facilitates the understanding of transmission dynamics of an outbreak, providing insights for outbreak prevention.