Abstract
The role of meticillin-resistant Staphylococcus aureus (MRSA) colonization of healthcare workers (HCWs), patients and the hospital environment in MRSA transmission in non-outbreak settings is poorly understood. To investigate transmission events (TEs) involving HCWs, patients and the environment under non-outbreak conditions in a hospital with a history of endemic MRSA using whole-genome sequencing (WGS). HCW (N= 326) and patient (N= 388) volunteers on nine wards were tested for nasal and oral MRSA colonization over two years. Near-patient environment (N= 1164), high-frequency touch sites (N= 810) and air (N= 445) samples were screened for MRSA. Representative MRSA and clinical isolates were analysed by WGS and core-genome multi-locus sequence typing (cgMLST). Closely related isolates (≤24 allelic differences) were segregated into related isolated groups (RIGs). In total, 155 MRSA were recovered: clinical isolates (N= 41), HCWs (N= 22), patients (N= 37), environmental isolates (N= 55). Nine clonal complexes (CCs) were identified among 110/155 MRSA sequenced with 77/110 assigned to CC22. Seventy-nine MRSA segregated into 17 RIGs. Numerous potential TEs were associated with CC22-MRSA (RIGs 1-15), CC45-MRSA (RIG-16) and CC8-MRSA (RIG-17). RIG-1, (the largest RIG) contained 24 ST22-MRSA-IVh from six HCWs, six patients, four clinical and eight environmental samples recovered over 17 months involving 7/9 wards. TEs involving HCW-to-patient, HCW-to-HCW, patient-to-patient and environmental contamination by HCW/patient isolates were evident. HCW, patient, clinical and environmental isolates were identified in four, nine, seven and 13 RIGs, respectively, with 12/13 of these containing isolates closely related to HCW and/or patient isolates. WGS detected numerous potential hospital MRSA TEs involving HCWs, patients and the environment under non-outbreak conditions.
Highlights
Meticillin-resistant Staphylococcus aureus (MRSA) have been endemic in Irish hospitals for several decades with ST22-MRSAIVh currently being predominant, accounting for 73.7% of MRSA bloodstream infections (BSIs) in 2019 [1,2]
The European antimicrobial-resistance surveillance network (EARS-Net) reported a 10% increase in S. aureus BSIs between 2014 and 2018. This included a 30% decrease associated with MRSA BSIs and a 20% increase associated with meticillin-susceptible S. aureus (MSSA) [3]
326 healthcare workers (HCWs) were enrolled in the study as described previously [4], of which 15/326 (4.6%) were colonized with MRSA
Summary
Meticillin-resistant Staphylococcus aureus (MRSA) have been endemic in Irish hospitals for several decades with ST22-MRSAIVh currently being predominant, accounting for 73.7% of MRSA bloodstream infections (BSIs) in 2019 [1,2]. The European antimicrobial-resistance surveillance network (EARS-Net) reported a 10% increase in S. aureus BSIs between 2014 and 2018. This included a 30% decrease associated with MRSA BSIs and a 20% increase associated with meticillin-susceptible S. aureus (MSSA) [3]. The frequency of HCW colonization by MRSA and their relatedness to MRSA recovered from patient and hospital environmental sources requires further investigation [13]. Routine screening of HCWs for MRSA is uncommon in most countries without a suspected epidemiological link between patient infections and HCWs [4]. Environmental MRSA are not routinely investigated in hospitals [4,9]
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