Incidence and control of Listeria monocytogenes in foods in Denmark

The Danish regulatory policy on Listeria monocytogenes in foods is based on the principles of HACCP and was developed using a health risk assessment approach. The Danish policy focuses examinations and criteria for L. monocytogenes in ready-to-eat foods and is based on a combination of inspection and product-testing. Based on current epidemiological information from several countries, a concentration of L. monocytogenes not exceeding 100 cfu/g of food at the time of consumption, seems to be of low risk to the consumers. In Denmark, ready-to-eat foods have been placed into six categories where absence of L. monocytogenes in 25 g is required in foods heat treated in the final package and in heat-treated as well as preserved, non heat-treated foods which can support growth within the shelf life. This level is necessary in foods capable of supporting growth, in order not to exceed 100 L. monocytogenes per g at the point of consumption. In heat-treated and preserved foods, which are not supportive of growth within the shelf-life and for raw, ready to eat foods, a level below 10 L. monocytogenes per g is regarded acceptable. A level between 10 and 100 L. monocytogenes per g is not satisfactory and a level above 100/g is not acceptable. Data on the qualitative and quantitative occurrence of L. monocytogenes in foods in Denmark are presented and discussed. In 1997 and 1998, greater than 15,000 samples from different categories of food were examined (semi-quantitatively) for the presence of L. monocytogenes. A significant difference could be seen in the number of samples containing more than 100 L. monocytogenes per g, between different categories of foods (1997, P = 0.001; 1998, P = 0.016). In 1997, preserved meat products and preserved fish products and to a lesser extent vegetables and meat or vegetable mayonnaise were more likely to contain high numbers (i.e. above 100 cfu/g) of L. monocytogenes than other food categories. In 1998, preserved meat products, but also heat-treated meat products, vegetables and meat or vegetable mayonnaise had the highest frequency of samples with > 100 L. monocytogenes per g. In a survey performed in 1994 and 1995, 1.3% of ready-to-eat food samples (heat-treated meat products, preserved meat and fish products) were found to be contaminated with L. monocytogenes at a level above 100 cfu/g. The samples included in this survey were primarily products produced by authorized companies and were comprised mainly of vacuum packed products or products packed in modified atmosphere and with long shelf lives, typically above several weeks. The corresponding percentages of positive samples primarily processed in the retail outlets (heat-treated meat products, preserved meat and fish products) in 1997 and 1998 were 0.3% and 0.6%, respectively. The results suggest that ready-to-eat meat and fish products with extended shelf-lives produced by authorized companies are more likely to contain high numbers (> 100 cfu/g) of L. monocytogenes than products processed in the retail sector which often have a shorter shelf life.