22/08/2014

 A European Union-wide baseline survey on Listeria monocytogenes was carried out in 2010 and 2011. Packaged (not frozen) hot or cold smoked or gravad fish, soft or semi-soft cheeses (excluding fresh cheeses) and packaged heat-treated meat products were sampled in 26 European Union Member States and in one country not belonging to the European Union. Multiple-factor analysis (Generalized Estimating Equations) was used to investigate the statistical association between several factors on which information was gathered during the baseline survey, and two outcomes: prevalence of Listeria monocytogenes and proportion of samples with counts exceeding 100 cfu/g, in the surveyed fish and meat products (no analysis is presented for cheese samples, owing to the small number of contaminated samples). Sparseness issues led to instability of the effect estimates for some of the factors. For fish samples, factors that exhibited a stable association with at least one of the two outcomes were ‗Subtype of the fish product‘ (factor related to the type of processing), ‗Number of antimicrobial preservatives and/or acidity regulators‘ and ‗Possible slicing‘. For meat products, the corresponding factors were ‗Type of the meat product‘, ‗Animal species of the origin of the meat product‘, ‗Possible slicing‘ and ‗Remaining shelf-life‘ (days between sampling and ‗Use by date‘). Furthermore, a statistical model was developed that allowed the use of estimates of the proportion of samples with an L. monocytogenes count > 100 cfu/g obtained from a single-unit sample survey of a population of RTE foods, in order to estimate the probability that if a five-unit sample had been taken from the same population, no individual unit, out of n = 5 units constituting the sample, would have exceeded the level of 100 cfu/g. The model was applied using data from the baseline survey for fish, cheese and meat products, at the end of shelf-life.