Methicillin-resistant Staphylococcus aureus outbreak in a veterinary teaching hospital: Potential human-to-animal transmission

During a 13-month period, fl equine patients visiting a veterinary teaching hospital for various diagnostic and surgical procedures developed postproc edural infections from,which methicillin (oxacillin)-resistant Staphylococc us aureus (MRSA) strains were isolated. The S, aureus isolates were identif ied by conventional methods that included Gram staining, tests for colonial morphology, tests for clumping factor, and tests for coagulase and urease activities and were also tested with the API STAPH IDENT system.;Antimicrob ial susceptibility tests were performed by the disk diffusion method. The b iochemical profile and antibiogram of each isolate suggested that the isola tes may have come from a common source. Because MRSA strains are very uncom mon animal isolates but are rather common human isolates, a nasal swab spec imen for culture was collected voluntarily from five persons associated,vit h equine surgery and recovery in an attempt to identify a possible source o f the organisms. MRSA strains were isolated from three of the five people, with one person found to be colonized,with two biotypes of MRSA, The MRSA i solates from the people appeared to be identical to the isolates from horse s. Further study of the isolates included SmaI and EagI macrorestriction an alysis by pulsed-field gel electrophoresis conducted in two different labor atories. The results indicated that both the equine and human isolates were members of a very closely related group which appear to have originated fr om a common source. On the basis of the pattern associated with the infecti on, it is speculated that the members of the Veterinary Teaching Hospital s taff were the primary source of the infection, although the specific mode o f transmission is unclear.