A 4-year outbreak of MRSA ST72-MRSA-IV spa type t1597 in a surgical high dependency unit in Ireland linked to repeated healthcare worker recolonisation

Abstract

Background: Patients undergoing cardiac surgery are identified as high risk for Staphylococcus aureus infection, including MRSA. An outbreak of MRSA was identified when two patients experienced MRSA infection concurrently in a cardiothoracic high dependency unit with uncommon detection of MRSA previously and an established screening programme.

Methods: An outbreak control team was convened and interventions applied including refresher training in hand and environmental hygiene, review of practice with regard to aseptic access of medical devices and consideration of antibiotic use in the unit. MRSA isolates were referred to the Irish National MRSA Reference Laboratory where spa typing assigned all isolates to t1597 and whole genome sequencing assigned them to multilocus sequence type ST72-MRSA-IV. Recovery of this strain from only this unit in Ireland and infrequent reporting in Europe prompted staff MRSA screening with two staff members found to harbour the outbreak strain. Despite successful decolonisation, recolonisation and further transmission to patients occurred.

Conclusions: In the clinical unit in which this outbreak occurred, the usual control measures to prevent spread of MRSA were in place. Recent Joint Healthcare Infection Society and Infection Prevention Society Guidance does not recommend routine staff screening for MRSA but does support its consideration in an outbreak of an unusual strain. In total, 9 patients and 2 staff were affected by this outbreak. There were 4 infections and 3 deaths. Sustained outbreak closure was necessary to protect certain national clinical programmes and was achievable only when colonised staff were no longer working in the unit.

Keywords: Cardiac surgery; Colonisation; Healthcare worker; MRSA; Outbreak; Screening.

Figure 1

Timeline of outbreak and implementation of interventions applied.

Figure 2

Distance based minimum spanning tree for 13 isolates based on core genome MLST of 1,861 genes, pairwise ignoring missing values generated by SepSphere ™ (Jünemann et al., 2013). Nodes are coloured by patient/staff member.