Infections caused by multidrug-resistant bacteria in an equine hospital (2012-2015)

Multidrug-resistant (MDR) bacteria are an emerging threat in human and veterinary medicine. There are few reports about infections caused by MDR isolates in horses. The aim of this study was to provide an overview of infections caused by MDR bacteria at the Equine Hospital Zurich between 2012 and 2015. Medical records were searched for horses with confirmed MDR bacterial infection. Multidrug resistance was defined according to human guidelines specific for each pathogen. MDR isolates were most commonly isolated from post-procedural infections (53/110, 48%), followed by musculoskeletal (16/110, 15%) and soft tissue infections (16/110, 15%). Escherichia coli (32/158, 20%) and Staphylococcus aureus (25/158, 16%) were the most common isolates. High resistance rates precluded therapy with commonly used antimicrobial drugs. The overall mortality rate was 20% (22/108) but depended on the localisation of the infection. Antimicrobial treatment prior to development of infection was reported for 89% (91/102) of horses. This study showed that MDR pathogens, mainly MDR E. coli and MRSA, cause a considerable number of infections in horses. A wide range of infections was seen, however, nosocomial infections predominated. These cases are typically hospitalised, pretreated with antibiotics, and suffering from comorbidities putting them at high-risk for acquiring infections caused by MDR isolates. The mortality of such infections was generally low but depended on site of infection.