Retrospective multicentre study of methicillin-resistant Staphylococcus aureus infections in 115 horses

Methicillin-resistant Staphylococcus aureus (MRSA) is an emerging veterinary and zoonotic pathogen, associated with increasing reports of disease in horses.

To provide an overview of the characteristics of clinical MRSA infections in horses.

A retrospective case study was performed on 115 horses admitted to 6 participating veterinary teaching hospitals in Canada and the United States between 2000 and 2006, and diagnosed with clinical MRSA infection. Descriptive statistics, univariate and multivariable analyses for community- (CA) vs. hospital-associated (HA) MRSA infections, and survival vs. nonsurvival at discharge were performed.

The age range of MRSA-infected horses was zero (born in hospital) to 31 years. HA (58/114, 50.9%) and CA infections (56/114, 49.1%) were equally common. Infection of surgical incisions was most frequently reported (44/115, 38.0%). Overall 93/111 (83.8%) cases survived to discharge. Previous hospitalisation and treatment with gentamicin were associated significantly with CA-MRSA, whereas infected incision sites were associated significantly with HA-MRSA. Factors significantly associated with nonsurvival included i.v. catheterisation, CA-MRSA infection and dissemination of infection to other body sites.

Equine MRSA infections have a broad range of clinical presentations, appear to be primarily opportunistic and the overall prognosis for survival to discharge is good.

These results should help direct future research with regard to investigation of risk factors for equine MRSA infection in community and hospital populations.