Identification and quantification of risk factors regarding Salmonella spp. on pork carcasses

The main elements of a descriptive epidemiological model for Salmonella spp. in Dutch pig slaughterlines, and the subsequent quantification of risk factors regarding the contamination of carcasses, are described. There is a strong correlation between the number of live animals that carry Salmonella spp. in their faeces and the number of contaminated carcasses at the end of the slaughterline. Live animals that carry Salmonella spp. are 3-4 times more likely to end up as a positive carcass than Salmonella-free animals. Currently, about 70% of all carcass contamination results from the animals themselves being carriers, and 30% because other animals were carriers (i.e. cross contamination). Furthermore, it is estimated that in general between 5-30% of the carcasses produced may contain Salmonella spp. With respect to carcass contamination with Enterobacteriaceae and Salmonella spp., inadequately cleaned polishing machines (odds ratio, OR, 6) and 'inapt procedures during evisceration' (OR 11), i.e. faulty evisceration and hygiene practices, are the most important risk factors. An estimated 5-15% of all carcass contamination with Salmonella spp. occurs during polishing after singeing. The remainder is the result of current evisceration practices (55-90%) and, to a lesser extent, further processing (5-35%), i.e dressing, splitting and meat inspection. Less likely Salmonella spp. already present on the skin of the live animals survive scalding and singeing. However, because pigs are the only important source for the Salmonella contamination of the line and the carcasses produced, it can also be concluded that if Salmonella-free pigs were produced, consumers could be provided with virtually Salmonella-free pork. As long as Salmonella-positive animals enter abattoirs, there will always be transmission of Salmonella spp. to consumers, even if the process is carried out according to stringent codes of good manufacturing practices (GMP). EU regulations should, therefore, allow for the decontamination of caracasses with a safe substance, e.g. lactic acid, on the condition that the slaughterhouse strictly adhers to GMP principles.