HEALTH RISK ASSESSMENT OF LISTERIA-MONOCYTOGENES IN CANADA

In this review, the major steps used in the formulation of a health ri sk assessment for Listeria monocytogenes in foods are discussed. Data is given on the numbers of human listeriosis cases reported in Canada along with the current Canadian regulatory policy on L. monocytogenes. Four major steps in the health risk assessment of this organism in fo od namely, hazard identification, hazard characterization, exposure as sessment and risk characterization, were examined. For hazard characte rization since it is known that no direct human dose response data is available for L. monocytogenes, a flexible dose response model called the Weibull-Gamma model was evaluated. For the exposure assessment, pa te and soft cheese, both high-risk foods in terms of listeriosis infec tion were used as prototypes in some of the models that were used. Usi ng disappearance data for cheese and 100 g as a typical serving, the d ata suggested an average of 102 servings per capita, per year in Canad a. As a rough approximation for L. monocytogenes, reference ID10 and I D90 dose levels of response for both normal and high risk populations were given as 10(7) and 10(9) for normal individuals, and 10(5) and 10 (7) for high-risk people. The corresponding dose response models were graphically displayed. These models exhibited a higher degree of susce ptibility and less host/pathogen heterogeneity for the higher risk gro up. The range of doses between the ID10 and ID90 reference values corr esponded roughly to levels associated with cases of listeriosis. In th e risk characterization stage, dose response data was combined with so me predictive growth modeling data of L. monocytogenes, on pate, assum ing an initial exposure of a single cell for food stored at 4 degrees and 8 degrees C. Storage of pate at 4 degrees C for more than 35 days resulted in a rapidly increasing risk for the high risk population, wh ile storage at 8 degrees C produced a similar risk after about 13 days . In addition, an equation, used to calculate the average probability of acquiring human listeriosis in Canada from soft and semi-soft chees e consumption, was formulated. Computations derived from this equation indicated a substantial level of consistency between reported data an d assumptions of the risk assessment model. An important part of risk characterization or possibly risk management is characterizing the eco nomic and social consequences of estimated risks. The total annual est imated cost of listeriosis illnesses and deaths in Canada was estimate d to be between 11.1 and 12.6 million dollars.