Comparison of two sampling and culture systems for detection of Salmonella enterica in the environment of a large animal hospital.

Abstract

REASONS FOR PERFORMING STUDY: Nosocomial salmonellosis is an important problem in veterinary hospitals that treat horses and other large animals. Detection and mitigation of outbreaks and prevention of healthcare-associated infections often require detection of Salmonella enterica in the hospital environment. OBJECTIVES: To compare 2 previously published methods for detecting environmental contamination with S.&#x2009;enterica in a large animal veterinary teaching hospital. STUDY DESIGN: Hospital-based comparison of environmental sampling techniques. METHODS: A total of 100 pairs of environmental samples were collected from stalls used to house large animal cases (horses, cows or New World camelids) that were confirmed to be shedding S.&#x2009;enterica by faecal culture. Stalls were cleaned and disinfected prior to sampling, and the same areas within each stall were sampled for the paired samples. One method of detection used sterile, premoistened sponges that were cultured using thioglycolate enrichment before plating on XLT-4 agar. The other method used electrostatic wipes that were cultured using buffered peptone water, tetrathionate and Rappaport-Vassiliadis R10 broths before plating on XLT-4 agar. RESULTS: Salmonella enterica was recovered from 14% of samples processed using the electrostatic wipe sampling and culture procedure, whereas S.&#x2009;enterica was recovered from only 4% of samples processed using the sponge sampling and culture procedure. There was test agreement for 85 pairs of culture-negative samples and 3 pairs of culture-positive samples. However, the remaining 12 pairs of samples with discordant results created significant disagreement between the 2 detection methods (P<0.01). CONCLUSIONS: Persistence of Salmonella in the environment of veterinary hospitals can occur even with rigorous cleaning and disinfection. Use of sensitive methods for detection of environmental contamination is critical when detecting and mitigating this problem in veterinary hospitals. These results suggest that the electrostatic wipe sampling and culture method was more sensitive than the sponge sampling and culture method.