Investigation and control of an outbreak of salmonellosis caused by multidrug-resistant Salmonella typhimurium in a population of hospitalized horses

An outbreak of salmonellosis in a population of hospitalized horses resulted in the closure of a teaching hospital for a period of 10 weeks. Fecal samples were collected from suspected cases and cultured for Salmonella. Salmonella isolates were characterized using antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE) and phage typing. Thirty-three cases of infection by a multidrug-resistant strain of S. typhimurium were detected. The index case was admitted on 26 August 1999. Fifteen (45%) cases occurred between April and June 2000. PFGE results suggested that this strain of S. typhimurium might have been introduced into the hospital environment by a foal presenting with diarrhea. The hospital was closed on June 13, and intensive environmental cleaning and disinfection were completed. Enforcement of infectious disease control protocols in hospitals and environmental and patient surveillance is needed to prevent outbreaks of salmonellosis.