Evaluation model of microbial contamination for pork production


<p>The Risk Assessment Unit of the Finnish Food Safety Authority Evira has developed a mathematical evaluation model, which can be utilised in general for the evaluation of the prevalence of microbes that endanger the purity of food. The model is based on the results of tests of different types performed separately on a sample of production animals at different stages of production.</p>

The production of domestic pork was used as an application example in the model. The material was gathered through monitoring of specific tagged pigs at the farm, in the slaughterhouse and ultimately in the form of meat samples. The test results and the model make it possible to evaluate the actual prevalence of microbes and any changes in it from one stage of the production chain to the next. The model makes allowance for the fact that microbes, although present, may not be detected in differently targeted samples taken at different points of the production chain , and that some observations may also be missing. The model can also be used to evaluate the effectiveness of microbe eradication action on the purity of food as well as other background variables that affect this risk. The output of the model is obtained in the form of a probability distribution, which describes the remaining uncertainty after data were included in the model. The magnitude of the microbial risk is measured by calculating probabilities and the results are then utilised in risk informed decision-making.

The application example consisted of a joint study on three adverse bacteria; Listeria monocytogenes, Yersinia enterocolitica and Yersinia pseudotuberculosis. The estimated prevalence of one or more of these bacteria in pork is 1-11 %. Through suitable action taken in the slaughterhouse, the prevalence level can be reduced to 0-2 %. The output of the model can be utilised in determining the ideal monitoring point for microbes and in planning risk control action for the production chain.

The model has been published in scientific journal Statistical Modelling 2010:69-97 (pdf, 578 kb)
Ranta, J., Siekkinen, K.-M., Nuotio, L., Laukkanen, R., Hellström, S., Korkeala, H., Maijala, R.
Causal hidden variable model of pathogenic contamination from pig to pork.

The model was developed within the framework of a research project in which also the Department of Food Hygiene and Environmental Health of the University of Helsinki participated.

Read more about the activities and studies of the Risk Assessment Research Unit  at Evira

For more information, please contact:
Senior Researcher Jukka Ranta
tel. +358 (0) 40 489 3374, jukka.ranta at-merkki-kapea.gif evira.fi

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