Methicillin-resistant Staphylococcus aureus (MRSA) are endemic in Irish hospitals and currently account for 21.5% of S. aureus bloodstream infections (BSIs). Many Northern-European countries have rates of 1-2%. Furthermore, methicillinsusceptible S. aureus (MSSA) BSIs have increased in recent years. MRSA colonisation of healthcare workers (HCWs) is reportedly higher in MRSA-endemic settings and HCWs have been implicated in MRSA and MSSA transmission to patients. Data on the role of S. aureus HCW colonisation in transmission to patients in MRSA-endemic settings is scarce with no published Irish data. Current Irish guidelines do not recommend routine S. aureus screening and decolonisation of HCWs. This study will investigate the prevalence, characteristics and transmission of MRSA and MSSA among HCWs, patients and environmental sites in a large Dublin hospital where MRSA is endemic, to determine if HCWs are a significant reservoir for S. aureus transmission to patients and whether national policy on screening and decolonisation requires revision. Sampling for S. aureus nasal and oropharyngeal colonisation among HCWs and patients and from environmental sites will be undertaken once quarterly for a year (powered to yield sufficient isolates). Patient clinical S. aureus isolates will also be investigated. All MRSA isolates will undergo whole-genome sequencing (WGS) because conventional typing offers poor discrimination of the predominant hospital clone (ST22-MRSA-IV). MSSA isolates will undergo spa typing and DNA microarray profiling to identify genotypes and representative isolates will undergo WGS. Pilot studies of ST22-MRSA-IV indicate that WGS detects significantly more transmission events than conventional typing and provides the discriminatory power to determine the temporal and transmission dynamics of S. aureus among HCWs, patients and the environment in an MRSAendemic setting. This study will provide an evidence base to inform HCW screening and decolonisation policies in MRSA-endemic settings, with the ultimate aim of reducing nosocomial S. aureus infections by reducing transmission from HCWs.
