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.

Prevalence, Enumeration, Serotypes, and Antimicrobial Resistance Phenotypes of Salmonella enterica Isolates from Carcasses at Two Large United States Pork Processing Plants

“…In particular, Salmonella occurrence on the skin of swine upon arrival in the abattoir and during the scalding/singeing/polishing process was identified as specific data gaps by the authors of a recent quantitative risk assessment model of the prevalence of Salmonella on swine carcasses (5). In the present study, samples were taken with sponges from three points along the pork processing line at two commercial U.S. pork processing facilities: the prescald carcass (postexsanguination), the preevisceration carcass (postscald, singe, and polish), and the chilled final carcass.…”

Salmonella enterica in Swine Production: Assessing the Association between Amplified Fragment Length Polymorphism and Epidemiological Units of Concern

“…Salmonella contamination of pork can be related to preharvest infection and postharvest cross-contamination (1,4). A recent quantitative risk assessment model aided by meta-analysis suggested that Salmonella-infected pigs entering the abattoir imparted a source of contamination during processing that explained 75% to 80% of the total contamination associated with carcasses (2). These proportions were estimated by construction of a linear regression model between the proportion of Salmonella carrier pigs entering the harvest lines and the proportion of contaminated eviscerated carcasses based on bootstrap simulation.…”

Meta-analysis of the incidence of foodborne pathogens in Portuguese meats and their products

“…Because Salmonella is primarily located in the gastrointestinal tract of sub-clinically infected pigs, they introduce the pathogen to the slaughterhouse through their internal organs, skin, faeces, and the cross-contamination of carcasses is basically a matter of redistributing Salmonella bacteria from positive pigs during the various slaughter processes. In a risk assessment model, Gonzales Barron et al (2009) underscored the need to target Salmonella contamination at swine production, calculating that on average 77% of the variability in the total contaminated carcasses at the point of evisceration is explained by the contamination from the carrier animals entering the slaughter lines. Thus, although in Portugal there is a national monitoring programme for Salmonella in pig meat based on sampling at slaughterhouse and meat cutting plants, the incidence of Salmonella in pork is still high, as its control requires rather a systematic approach from farm to fork with specific risk management strategies in place also at farm level.…”