Assessment of the diagnostic accuracy of bacteriological culture and the invA-gen-based PCR for the detection of Salmonella organisms from caecal content from slaughtered pigs through Bayesian approaches

Abstract

The goal of this study was to determine the accuracy of a culture technique and the invA-genbased PCR, for the detection of Salmonella spp from caecal samples from slaughtered pigs. For this purpose a Bayesian approach was used. Two hundred and three pigs were used. Animals were grouped into 2 populations: 96 from small farms and 1 07 from large farms. Sensitivity was 56% (95% Credible Interval: 40-76) for culture and 91% (95%CI : 81-97) for PCR. The specificity of the PCR was 88% (95%CI: 80-95). According to these estimates. the percentage of p1gs with Salmonella organisms in the1r faeces at slaughter in this population was at least 25.5%. It IS concluded that bacteriology on caecal samples alone is a poor diagnostic method to carry out studies on the prevalence of salmonellosis in pigs, and that the sensittvity of th1s technique would be probably lower if the procedure is simplified or 1s carried out on non-stressed pig populations. PCR was considered a reliable screening method for the diagnosis of pig salmonellosis but prone to some misclassifications that should be considered if this technique is used.