Listeria spp. in food processing, non-food and domestic environments

The occurrence of Listeria spp. was investigated in 17 food factories (representing six different product groups), 35 Dutch households and in a sawmill. The aim of this study was to assess their distribution in these environments, possible measures for their control and the likelihood of human exposure to these organisms from sources other than foods or faeces. In food factories, listerias were found in drains, floors, standing water, residues and food-contact surfaces in descending order of frequency. In two dry culinary food units, no samples were found to be contaminated. These results indicate that dry conditions and the restriction of food residues contribute to the control of these organisms. From kitchens in 35 households chosen at random, seven (20%) were found to be contaminated with listerias. They were isolated from refrigerators (one swab), dish cloths (six from seven samples) and from two dustbins. It seems that dish cloths could be an important source of these organisms in the home. In the environment of the sawmill, L. ivanovii was isolated more frequently than any other species. This was interpreted in terms of the availability of xylose, a wood breakdown product, in such environments. Although listeriosis outbreaks have been associated with foods, most cases are of unknown origin. This study indicates that listerias are common in many environments and that epidemiological studies should concentrate on these as well as foods. In view of the large number of sources of listerias in the natural environment, the domestic environment and in raw foods prepared in the home, human beings are exposed to these organisms on a regular basis. Scrupulous personal and domestic hygiene to diminish cross-contamination could be an important factor in the prevention of human listeriosis.