Equine Hospital Salmonella Biosecurity Evaluation

Salmonella infection is a disease taken very seriously by equine veterinarians, partly because it can cause severe gastrointestinal disease in their patients, and also because it can do the same to the veterinarians and hospital staff. Thus, most equine hospitals have biosecurity measures in place to avoid the spread of Salmonella (or any other infectious organism) that comes into the hospital.

"Most large animal hospitals have a 'zero tolerance' goal for nosocomial (hospital-acquired) salmonellosis," noted Harold C. Schott, II, DVM, PhD, Dipl. ACVIM, professor of large animal clinical sciences at Michigan State University (MSU). He discussed the evolution of the Salmonella biosecurity program at MSU over the last 10 years during the 2009 American Association of Equine Practitioners convention, held Dec. 6-10 in Las Vegas, Nev.

"Although zero tolerance may be the goal, infectious organisms can be introduced to a hospital with any horse (healthy or sick), and spread between patients can occur rapidly," he said. "Thus, the true goal of a biosecurity program is to rapidly identify when 'bad bugs' may enter a hospital and limit the risk of spread to other horses and/or personnel. Further, biosecurity programs often need to be tailored for both the infectious agent and specific hospital design."

Numerous measures are typically used in biosecurity programs, he said. These might include:

  • Establishing traffic flow patterns (i.e., treat infectious horses last);
  • Detail specific indications for patient isolation (i.e., known Salmonella infection or contact with a Salmonella case);
  • Cohort housing of patients at various risk levels (such as keeping the gastrointestinal cases together and away from the reproduction unit);
  • Screening patients for fecal shedding of Salmonella;
  • Monitoring efficacy of disinfection practices with environmental cultures;
  • Encouraging good hygiene by staff members.

These practices tend to vary across facilities based on facility design and other specific challenges, he noted. To evaluate whether the practices in effect at a particular hospital are working, one must evaluate records over several years to see if the frequency and severity of outbreaks have decreased.

Schott reported that there were four Salmonella outbreaks at MSU between 1997 and 2006. This time period began with a pretty solid biosecurity program for Salmonella due to an outbreak in 1996. All horses admitted for gastrointestinal (GI) problems had fecal tests for Salmonella performed on admittance, and horses with a primary complaint of diarrhea were admitted directly to isolation. Impenetrable gowns, double protective booties, gloves, and caps were used for personnel handling all isolated horses, and equipment such as thermometers and buckets were supplied one to each isolated horse.

During the study period, Schott noted the following findings:

  • On average, 2,535 horses were treated at MSU per year from 2000-2006, with 1,221 being admitted for inpatient treatment.
  • An average of 335 GI cases had fecal samples taken each year (often repeatedly), for 9,519 samples submitted annually. Positive results were found in 1.3% of them on average, but positives were seen in more than 3% of samples in 1997, 1999, 2001-2003, and 2006.
  • Four outbreaks occurred--in 1997, 2001, 2003, and 2006. The first outbreak was considered to be a continuation of a 1996 outbreak.
  • The 2001 outbreak was found to have resulted from contamination in the referring practice, where dairy calves with Salmonella diarrhea were treated next to horse stalls (accounting for five of 12 affected horses in 2001). Following this outbreak, further separation of GI cases from the rest of the hospital population and increased barrier protocols (gowns, masks, etc.) were implemented.
  • In 2003 only one horse developed salmonellosis in the hospital, but other horses were colonized with the organism in different wards. Personnel transmission was suspected, and complete re-gowning began to be required between isolation patients. In addition, boxes of gloves were placed by each stall throughout the hospital, and separate shovels/lead ropes were assigned per stall in the GI ward.
  • In 2006 a mild outbreak in the colic ward occurred, but the Salmonella variant was quite susceptible to antibiotics and was quickly eradicated.

"Control of nosocomial infections is important in any type of large animal hospital," Schott concluded. "Protocols must be developed and placed into practice to identify when an increasing number of infections are occurring in order that a rapid and effective method of controlling outbreaks may be undertaken. As illustrated by our experiences, when surveillance for disease is implemented, the opportunity to detect outbreaks of both nosocomial disease and colonization is also increased.

"Unfortunately, improved biosecurity programs are not always completely effective in limiting nosocomial infection rates," he added. "Thus, biosecurity remains an ongoing challenge that requires strict compliance to protocols coupled with effective communication to encourage all personnel to understand why such protocols are necessary. Furthermore, ongoing evaluation of the efficacy of biosecurity programs and regular re-evaluation of protocols used is critical in the effort to reduce Salmonella nosocomial infection rates in equine hospitals."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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