Frequent undetected MRSA ward-based transmission linked to patient sharing between hospitals

Abstract

Background

Recent evidence suggests hospital transmission of methicillin-resistant Staphylococcus aureus (MRSA) is uncommon in UK centers that have implemented sustained infection control programmes. We investigated whether a healthcare-network analysis could shed light on transmission paths currently sustaining MRSA levels in UK hospitals.

Methods

A cross-sectional observational study was performed in two NHS hospital groups and a general district hospital in South-East London. All MRSA patients identified at inpatient, outpatient and community settings between 1^st November 2011 and 29^th February 2012 were included. We identified genetically-defined MRSA transmission clusters in individual hospitals and across the healthcare-network, and examined genetic differentiation of ST22 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 ('I').

Results

248/610 (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 26/32 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 ≤ 0.01).

Conclusions

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.