Diagnostic performance and application of a real-time PCR assay for the detection of Salmonella in fecal samples collected from hospitalized horses with or without signs of gastrointestinal tract disease

• Evaluation of the diagnostic performance of a real-time PCR assay targeting the Salmonella invA gene.
• Evaluation in horses with or without signs of gastrointestinal (GI) disease.
• The PCR assay had a high (100%) negative predictive value.
• The PCR assay can be used as a screening test for detection of Salmonella in feces of horses.

The main objective of this study was to assess the diagnostic performance of a real-time polymerase chain reaction (PCR) assay for the detection of Salmonella in fecal samples collected from hospitalized horses with or without signs of gastrointestinal (GI) tract disease. The PCR assay used primers and a probe that targeted the invA gene of Salmonella. Assuming a sensitivity of 100% and a specificity of 96.6%, and a disease prevalence of 2%, 5%, and 10–15% in study horses, the PCR assay had a high (100%) negative predictive value, and a positive predictive value that ranged from 37% in horses without signs of GI disease that tested Salmonella culture-negative, to 60% in horses with signs of GI disease that tested Salmonella culture-negative, to 76–83% in horses with signs of GI disease that tested Salmonella culture-positive. This study provides evidence that the real-time PCR that targets the Salmonella invA gene can be used as a screening test for the detection of Salmonella in feces of hospitalized horses with signs of GI disease. Horses that test PCR-positive can be tested in series using bacteriologic culture to reduce false positive results or to provide additional data (e.g., antibiogram and serotyping data) that can be used to identify potential nosocomial Salmonella infections.