Abstract
Recent evidence suggests that hospital transmission of methicillin-resistant Staphylococcus aureus (MRSA) is uncommon in UK centers that have implemented sustained infection control programs. We investigated whether a healthcare-network analysis could shed light on transmission paths currently sustaining MRSA levels in UK hospitals. A cross-sectional observational study was performed in 2 National Health Service hospital groups and a general district hospital in Southeast London. All MRSA patients identified at inpatient, outpatient, and community settings between 1 November 2011 and 29 February 2012 were included. We identified genetically defined MRSA transmission clusters in individual hospitals and across the healthcare network, and examined genetic differentiation of sequence type (ST) 22 MRSA isolates within and between hospitals and inpatient or outpatient and community settings, as informed by average and median pairwise single-nucleotide polymorphisms (SNPs) and SNP-based proportions of nearly identical isolates. Two hundred forty-eight of 610 (40.7%) MRSA patients were linked in 90 transmission clusters, of which 27 spanned multiple hospitals. Analysis of a large 32 patient ST22-MRSA cluster showed that 26 of 32 patients (81.3%) had multiple contacts with one another during ward stays at any hospital. No residential, outpatient, or significant community healthcare contacts were identified. Genetic differentiation between ST22 MRSA inpatient isolates from different hospitals was less than between inpatient isolates from the same hospitals (P ≤ .01). There is evidence of frequent ward-based transmission of MRSA brought about by frequent patient admissions to multiple hospitals. Limiting in-ward transmission requires sharing of MRSA status data between hospitals.
Highlights
Recent evidence suggests that hospital transmission of methicillin-resistant Staphylococcus aureus (MRSA) is uncommon in UK centers that have implemented sustained infection control programs
Two hundred forty-eight of 610 (40.7%) MRSA patients were linked in 90 transmission clusters, of which 27 spanned multiple hospitals
Analysis of a large 32 patient ST22-MRSA cluster showed that 26 of 32 patients (81.3%) had multiple contacts with one another during ward stays at any hospital
Summary
A cross-sectional observational study was performed in 2 National Health Service hospital groups and a general district hospital in Southeast London. All MRSA patients identified at inpatient, outpatient, and community settings between 1 November 2011 and 29 February 2012 were included. All MRSA isolates identified over 4 months (November 2011 to February 2012) were collected from 3 National Health Service (NHS) hospital microbiology laboratories collectively serving a population of 867 254 usual residents [18] and providing service to all inpatients, outpatients, and surrounding primary community-based healthcare facilities (ie, general practices [GPs]) in Lambeth, Southwark, and Lewisham boroughs of Southeast London. Participating centers comprised 4 acute tertiary-referral hospitals in 2 NHS hospital groups (Guy’s and St Thomas’ NHS Foundation Trust [GSTT; hospital A] and King’s College NHS Foundation Trust [hospital B]) plus 1 acute District General Hospital (University Hospital Lewisham [hospital C]). Clinical location data were aggregated for analysis into settings (defined as inpatient, outpatient, or community) linked to each participant hospital. Whole-genome sequencing (WGS) was conducted at Illumina UK on the first confirmed MRSA isolate from each patient at each unique clinical location over the study period as described previously [16, 17]
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