A meta-analysis study of the effect of chilling on prevalence of Salmonella on pig carcasses

In the field of food safety, meta-analysis can be used to combine results of prevalence studies of pathogens at critical stages within the food processing chain so that policy makers can access reliable and concise information on the effectiveness of interventions for controlling and preventing foodborne illnesses in humans. The objective of this work was to demonstrate the applicability of a parametric approach of meta-analysis to the specific case of determining the overall effect of chilling on Salmonella prevalence on pig carcasses. A meta-analysis was performed on each of two parameters measuring effect size for binary outcomes (relative risk and risk difference). Both meta-analyses confirmed that the chilling operation has a significant beneficial effect (P < 0.001) on the reduction of Salmonella prevalence on pig carcasses. Because risk difference is a parameter sensitive to the differences across studies in carcass swab areas and Salmonella detection methods, its meta-analysis highly reflected this heterogeneity (P < 0.001). However, parameterization of relative risk, not being biased by the above sources of variability, did not give rise to heterogeneity among studies and produced a fixed-effects meta-analysis solution, which is deemed more suitable for compilations based on a small number of individual studies (n = 9). Because of the systematic approach of meta-analysis (i.e., individual studies are weighed according to precision) and its reliance for actual data, the output distribution of the relative risk effect size (approximately eN(-0.868,0.166)) merits consideration for inclusion in the chilling stage of quantitative risk assessments modeling the prevalence of this pathogen along the pork production chain.