Meticillin-resistant Staphylococcus aureus transmission among healthcare workers, patients and the environment in a large acute hospital under non-outbreak conditions investigated using whole-genome sequencing.

Abstract

BACKGROUND\nThe role of MRSA colonization of healthcare workers (HCWs), patients and the hospital environment in MRSA transmission in non-outbreak settings is poorly understood.\n\n\nAIMS\nTo 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).\n\n\nMETHODS\nHCW (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=1,164), 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 multilocus sequence typing (cgMLST). Closely-related isolates (≤24 allelic differences) were segregated into related isolated groups (RIGs).\n\n\nFINDINGS\nIn 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.\n\n\nCONCLUSIONS\nWGS detected numerous potential hospital MRSA TEs involving HCWs, patients and the environment under non-outbreak conditions.