Statistical process control methods used to evaluate the serologic responses of pigs infected with three Salmonella serovars

Abstract

Objectives: To confirm that the mix-ELISA detects antibody against Salmonella serovars Typhimurium, Infantis, and Choleraesuis; to demonstrate that statistical process control (SPC) methods can be used to validate the mix-ELISA; and to demonstrate how SPC can be used to assess the Salmonella serologic status of swine. Methods: Three groups of pigs were inoculated with Salmonella Typhimurium, Salmonella Choleraesuis, or Salmonella Infantis (one serovar per group). Serologic responses were measured with the mix-ELISA and compared to responses of a group of uninfected pigs. Mix-ELISA results were evaluated using SPC methods to calculate a positive-negative cutoff value and to determine assay diagnostic sensitivity and specificity. The SPC results were compared to results of receiver operator characteristic (ROC) curve analysis. Results: Three cutoffs were determined from the SPC methods: group average (optical density [OD]% > 7.239), group range (OD% range ≥ 12.61), and individual (OD% ≥ 12). ROC curve analysis also showed optimized sensitivity (0.845) and specificity (1.00) when the individual cutoff was OD% ≥ 12.5. The OD% values were highest in pigs infected with Salmonella Typhimurium. Implications: The mix-ELISA detects antibody in pigs infected with Salmonella serovars, including Choleraesuis. Statistical process control methods can be used with mix-ELISA results to determine diagnostic cutoff values for assessing Salmonella serologic status. The degree of Salmonella exposure in swine can be assessed using SPC methods.