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Title: Detection and control of a nosocomial outbreak caused by Salmonella Newport at a large animal hospital

Author
item STENERODEN, KATIE - Colorado State University
item VAN METRE, DAVID - Colorado State University
item Jackson, Charlene
item MORLEY, PAUL - Colorado State University

Submitted to: Journal of Veterinary Internal Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2010
Publication Date: 5/25/2010
Citation: Steneroden, K.K., Van Metre, D.C., Jackson, C.R., Morley, P.S. 2010. Detection and control of a nosocomial outbreak caused by Salmonella Newport at a large animal hospital. Journal of Veterinary Internal Medicine. 24(3):606-616.

Interpretive Summary: Active surveillance, early recognition, and aggressive mitigation are all important steps to control nosocomial outbreaks in veterinary hospitals. In 2006, these strategies were employed during an outbreak of Salmonella enterica serotype Newport in a large animal hospital in Colorado. S. Newport was isolated from animals including alpacas, goats, and horses as well as the environment including animal stalls, treatment rooms, and floors. During the entire period of shedding and environmental contamination with the outbreak strain, a total of 427 fecal samples were collected from 234 patients to screen for S. enterica shedding. Of these, 13.2% (31/234) of patients and 10.8% (46/427) of fecal samples were culture-positive (including the eight patients which shed the outbreak strain). One patient, a 10 year old Quarter Horse, developed severe enterocolitis, diarrhea, and septicemia and subsequently died. The S. Newport outbreak strain was resistant to amoxicillin-clavulanate, ampicillin, ceftiofur, cephalothin, chloramphenicol, streptomycin, sulfonamide, and tetracycline and was susceptible to amikacin, gentamicin, enrofloxacin, and trimethoprim-sulfamethoxazole. PFGE analysis of the isolates showed a high degree of genetic relatedness. Infection control, biosecurity standard operating procedures, continued sampling and rigorous cleaning and disinfection were employed until Salmonella was no longer recovered after culture of the samples. This case study provides useful information for veterinarians, epidemiologists, and veterinary hospitals in order to control nosocomial outbreaks without closure of the facility.

Technical Abstract: Objective – To describe active surveillance, early recognition, and aggressive mitigation efforts that allowed control of an outbreak of nosocomial S. Newport infections in a large referral hospital without closure. Design – Longitudinal outbreak investigation Procedures – An outbreak of S. Newport infections was detected among hospitalized large animal patients using ongoing, standardized surveillance techniques. Patient and environmental microbiologic data were analyzed to identify temporal and spatial relationships affecting the spread of a single S. Newport strain among patients and within the hospital environment. Data were also summarized relative to standardized and special mitigation efforts that were employed during the outbreak. The genetic relatedness of the S. Newport isolates obtained from patients and environmental samples was investigated using pulsed-field gel electrophoresis (PFGE). Results – Of 145 large animal patients sampled, 8 (5.6%) were found to be infected with the strain of S. Newport that was associated with this outbreak. This strain was isolated from 1 of 32 samples obtained from previously-occupied stalls after disinfection. However, this strain was isolated from 14.2% (42/295) of environmental samples obtained from hand-contact, floor, or composite hand-contact and floor surfaces outside of patient stalls, indicating that widespread environmental contamination occurred during the outbreak. These data were used to guide patient isolation, disinfection, and other mitigation efforts. Through PFGE analysis, multiple isolates of S. Newport obtained from infected inpatients and the environment showed a high degree of genetic relatedness, confirming clonal dissemination. Conclusions and Clinical Relevance – Extensive patient and environmental surveillance and persistent mitigation efforts can be used to control a nosocomial Salmonella outbreak without resorting to hospital closure.