Qualitative and quantitative contamination of ready-to-eat food-stuffs with the pathogen Listeria monocytogenes was studied in 1586 samples collected from 103 supermarkets (n = 946) and 61 households (n = 640) in Vienna, Austria.
Seventeen groups of ready-to-eat foods were classified into three risk categories for contamination (CP1–CP3).
Three to four samples were randomly collected at the retail level from each CP.
Regarding the households, the sampling procedure was started with food items of CP1, and if not available, was continued with sampling of food items of CP2 and finally of CP3.
Additionally, 184 environmental samples (swabs from the kitchen area, dust samples from the vacuum cleaner) and faecal samples (household members and pet animals) were included.
One-hundred and twenty-four (13.1%) and 45 (4.8%) samples out of 946 food samples collected from food retailers tested positive for Listeria spp. and L. monocytogenes, respectively, with five smoked fish samples exceeding the tolerated limit of 100 CFU/g food.
Food-stuffs associated with the highest risk of contamination were twice as frequently contaminated with L. monocytogenes as food-stuffs associated with a medium risk of contamination.
Products showing the highest contamination rate were fish and seafood (19.4%), followed by raw meat sausages (6.3%), soft cheese (5.5%) and cooked meat products/patés (4.5%).
The overall contamination rate of foods collected at the household level was more than two times lower.
Only 5.6% and 1.7% of 640 food-stuffs analysed tested positive for Listeria spp. and L. monocytogenes, respectively.
However, CP1 foods were rarely collected.
Pulsed-field gel electrophoresis (PFGE) typing of the collected L. monocytogenes isolates revealed a high degree of diversity between the isolates, with some exceptions.
PFGE typing of isolates harvested from green-veined cheese revealed a match among strains, although the manufacturer seemed to be distinguishable.
Typing of household strains revealed an epidemiological link within one family.
In this case, food-stuffs and the kitchen environment were contaminated by an indistinguishable isolate.
In addition, the same isolate was collected from a pooled faecal sample of the household members suggesting that consumption of even low contaminated food items (<100 CFU/g) results in Listeria shedding after the passage through the gut.
Source: M. Wagner, B. Auer, C. Trittremmel, I. Hein, D. Schoder (2007): Survey on the Listeria Contamination of Ready-to-Eat Food Products and Household Environments in Vienna, Austria. In: Zoonoses and Public Health 54 (1), 16–22.
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