Risk Analysis, Vol. 00, No. 0, 2014 DOI: 10.1111/risa.12332 Farm to Fork Quantitative Risk Assessment of Listeria monocytogenes Contamination in Raw and Pasteurized Milk Cheese in Ireland Uma Tiwari, 1 Enda Cummins, 2 Antonio Valero, 3 Des Walsh, 1 Marion Dalmasso, 4 Kieran Jordan, 4 and Geraldine Duffy 1,* The objective of this study was to model and quantify the level of Listeria monocytogenes in raw milk cheese (RMc) and pasteurized milk cheese (PMc) from farm to fork using a Bayesian inference approach combined with a quantitative risk assessment. The modeling approach included a prediction of contamination arising from the farm environment as well from cross-contamination within the cheese-processing facility through storage and subse- quent human exposure. The model predicted a high concentration of L. monocytogenes in contaminated RMc (mean 2.19 log 10 CFU/g) compared to PMc (mean -1.73 log 10 CFU/g). The mean probability of illness (P 1 for low-risk population, LR) and (P 2 for high-risk popu- lation, HR, e.g., immunocompromised) adult Irish consumers following exposure to contam- inated cheese was 7 × 10 -8 (P 1 ) and 9 × 10 -4 (P 2 ) for RMc and 7 × 10 -10 (P 1 ) and 8 × 10 -6 (P 2 ) for PMc, respectively. In addition, the model was used to evaluate performance objec- tives at various stages, namely, the cheese making and ripening stages, and to set a food safety objective at the time of consumption. A scenario analysis predicted various probabilities of L. monocytogenes contamination along the cheese-processing chain for both RMc and PMc. The sensitivity analysis showed the critical factors for both cheeses were the serving size of the cheese, storage time, and temperature at the distribution stage. The developed model will allow food processors and policymakers to identify the possible routes of contamination along the cheese-processing chain and to reduce the risk posed to human health. KEY WORDS: Bayesian inference; dose response; L. monocytogenes; pasteurized milk cheese; raw milk cheese; risk assessment 1. INTRODUCTION The presence of Listeria monocytogenes in the dairy-processing chain is a persistent challenge for 1 Teagasc Food Research Food Centre, Ashtown, Dublin, Ireland. 2 School of Biosystems Engineering, University College Dublin, Dublin, Ireland. 3 Department of Food Science and Technology, University of Cor- doba, Cordoba, Spain. 4 Teagasc Food Research Centre, Moorepark, Fermoy, Co. Cork, Ireland. ∗ Address correspondence to Geraldine Duffy, Teagasc Food Research Food Centre, Ashtown, Dublin 15, Ireland; Geral- dine.duffy@teagasc.ie. dairy food safety. (1) Outbreaks of listeriosis in humans related to the consumption of contami- nated dairy products have been reported in many countries, (2,3) including listeriosis outbreaks in Eu- ropean countries linked to cheese made from raw milk. (4,5) In some of these listeriosis cases, postpas- teurization contamination had occurred. For exam- ple, an outbreak of listeriosis in Germany related to contaminated pasteurized milk cheese (PMc) af- fected 189 people between October 2006 and Febru- ary 2007. (6) There is potential for contamination of raw milk with L. monocytogenes in the dairy farm environment. (6–8) Sources of such contamination may 1 0272-4332/14/0100-0001$22.00/1 C  2015 Society for Risk Analysis