In this review, the major steps used in the formulation of a health risk 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 foods, namely, hazard identification, hazard characterization, exposure assessment and risk characterization, were examined. For hazard characterization, 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, pâté and soft cheese, both high-risk foods in terms of listeriosis infection, were used as prototypes in some of the models that were used. Using disappearance data for cheese and 100 g as a typical serving, the data suggested an average of 102 servings per capita, per year in Canada. As a rough approximation, for L. monocytogenes, reference ID10 and ID90 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 susceptibility and less host/pathogen heterogeneity for the higher risk group. The range of doses between the ID10 and ID90 reference values corresponded roughly to levels associated with cases of listeriosis. In the risk characterization stage, dose response data was combined with some predictive growth modeling data of L. monocytogenes on pâté, assuming an initial exposure of a single cell for food stored at 4 degrees and 8 degrees C. Storage of pâté at 4 degrees C for more than 35 days resulted in a rapidly increasing risk for the high risk population, while 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 cheese consumption, was formulated. Computations derived from this equation indicated a substantial level consistency between reported data and assumptions of the risk assessment model. An important part of risk characterization or possibly risk management is characterizing the economic and social consequences of estimated risks. The total annual estimated cost of listeriosis illnesses and deaths in Canada was estimated to be between 11.1 and 12.6 million dollars.
The present situation regarding Listeria monocytogenes and ready-to-eat (RTE) seafood is discussed. An updated regulatory policy on L. monocytogenes directs inspection and compliance action to those RTE foods capable of supporting growth of the organism and is based on a combination of inspection, environmental sampling and product testing. The incidence of L. monocytogenes in imported seafood products in 1996-1997 and 1997-1998 was 0.88 and 0.3%, respectively. With respect to domestic products, an analysis of 347 RTE foods in 1997-1998 and 1998-1999, at one of the large fish inspection labs in the Maritimes, revealed an absence of L. monocytogenes. The only seafood product linked to suspect cases of listeriosis in Canada was imported.