Running head : Exposure assessment of L . monocytogenes in goat - cheese 1 Retrospective analysis of a Listeria monocytogenes contamination episode in 2 raw milk goat cheese using quantitative microbial risk assessment tools

24 In 2005, the Belgian authorities reported a Listeria monocytogenes contamination episode in 25 cheese made from raw goat’s milk. The presence of an asymptomatic shedder goat in the herd 26 caused this contamination. On the basis of data collected at the time of the episode, a 27 retrospective study was performed using an exposure assessment model covering the 28 production chain from the milking of goats up to delivery of cheese to the market. Predictive 29 microbiology models were used to simulate the growth of L. monocytogenes during the 30 cheese process in relation with temperature, pH and water activity. The model showed 31 significant growth of L. monocytogenes during chilling and storage of the milk collected the 32 day before the cheese production (median increase of 2.2 log CFU/ml) and during adjunction 33 of starter and rennet to milk (median increase of 1.2 log CFU/ml). The L. monocytogenes 34 concentration in the fresh unripened cheese was estimated to be 3.8 log CFU/g (median). This 35 result is consistent with the number of L. monocytogenes in the fresh cheese (3.6 log CFU/g) 36 reported during the cheese contamination episode. A variance-based method sensitivity 37 analysis identified the most important factors impacting the cheese contamination, and a 38 scenario analysis then evaluated several options for risk mitigation. Thus, by using 39 Quantitative Microbial Risk Assessment (QMRA) tools, this study provides reliable 40 information to identify and control critical steps in a local production chain of cheese made 41 from raw goat’s milk. 42 43