Estimation of Prevalence of Salmonella on Pig Carcasses and Pork Joints, Using a Quantitative Risk Assessment Model Aided by Meta-Analysis

Abstract

This risk assessment study aimed to estimate the prevalence of Salmonella on pig carcasses and pork joints produced in slaughterhouses, on the basis that within groups of slaughter there is a strong association between the proportion of Salmonella-positive animals entering the slaughter lines (x) and the resulting proportion of contaminated eviscerated pig carcasses (y). To this effect, the results of a number of published studies reporting estimates of x and y were assembled in order to model a stochastic weighted regression considering the sensitivities of the diverse Salmonella culture methods. Meta-analysis was used to assign weights to the regression and to estimate the overall effect of chilling on Salmonella incidence on pig carcasses. The model's ability to produce accurate estimates and the intrinsic effectiveness of the modeling capabilities of meta-analysis were appraised using Irish data for the input parameter of prevalence of Salmonella carrier slaughter pigs. The model approximated a Salmonella prevalence in pork joints from Irish boning halls of 4.0% (95% confidence interval, 0.3 to 12.0%) and was validated by the results of a large survey (n = 720) of Salmonella in pork joints (mean, 3.3%; 95% confidence interval, 2.0 to 4.6%) carried out in four commercial pork abattoirs as part of this research project. Sensitivity analysis reinforced the importance of final rinsing (r = −0.382) and chilling (r = −0.221) as stages that contribute to reducing considerably the occurrence of Salmonella on the final product, while hygiene practices during jointing seemed to moderate only marginally the amount of contaminated pork joints. Finally, the adequacy of meta-analysis for integrating different findings and producing distributions for use in stochastic modeling was demonstrated.