Infection prevention and control interventions in the first outbreak of methicillin-resistant Staphylococcus aureus infections in an equine hospital in Sweden

Abstract

Background: The first outbreak of methicillin-resistant Staphylococcus aureus (MRSA) infection in horses in Sweden occurred in 2008 at the University Animal Hospital and highlighted the need for improved infection prevention and control. The present study describes interventions and infection prevention control in an equine hospital setting July 2008 - April 2010.

Method: This descriptive study of interventions is based on examination of policy documents, medical records, notes from meetings and cost estimates. MRSA cases were identified through clinical sampling and telephone enquiries about horses post-surgery. Prospective sampling in the hospital environment with culture for MRSA and genotyping of isolates by spa-typing and pulsed-field gel electrophoresis (PFGE) were performed.

Results: Interventions focused on interruption of indirect contact spread of MRSA between horses via staff and equipment and included: Temporary suspension of elective surgery; and identification and isolation of MRSA-infected horses; collaboration was initiated between authorities in animal and human public health, human medicine infection control and the veterinary hospital; extensive cleaning and disinfection was performed; basic hygiene and cleaning policies, staff training, equipment modification and interior renovation were implemented over seven months.Ten (11%) of 92 surfaces sampled between July 2008 and April 2010 tested positive for MRSA spa-type 011, seven of which were from the first of nine sampling occasions. PFGE typing showed the isolates to be the outbreak strain (9 of 10) or a closely related strain. Two new cases of MRSA infection occurred 14 and 19 months later, but had no proven connections to the outbreak cases.

Conclusions: Collaboration between relevant authorities and the veterinary hospital and formation of an infection control committee with an executive working group were required to move the intervention process forward. Support from hospital management and the dedication of staff were essential for the development and implementation of new, improved routines. Demonstration of the outbreak strain in the environment was useful for interventions such as improvement of cleaning routines and interior design, and increased compliance with basic hygienic precautions. The interventions led to a reduction in MRSA-positive samples and the outbreak was considered curbed as no new cases occurred for over a year.

Figure 1

Surfaces testing positive for MRSA in ward A of the equine hospital. Samples from July 2008. Dots denote positive environmental samples: Yellow - door knobs, Blue - ISO, Turquoise - cribs and salt stones, Brownish-red - sling/traverse (see also Table 2). Some dots represent pooled samples e.g. in the lameness run-up, one cloth was used in 21 door knobs making one pooled sample and in Stall A several salt stones + cribs were sampled with one cloth. Green area is the surgery unit. The smaller green area is 'room 3' for standing surgery procedures. The pinkish-brown squares are stalls housing MRSA-positive horses during the outbreak. 1 - Stable A, 2 - arrow towards ward B, 3 - stable yard, 4 - isolation unit in ward A, 5 - front desk, 6 - main entrance, 7 - lameness run-up corridor.

Figure 2

PFGE pattern with ApaI restriction enzyme showing different pulsotypes of environmental MRSA isolates spa-type t011. One band of difference (arrow), Right lane - pulsotype A. Left lane - pulsotype A1.