EFSA assesses prevalence and compliance of Listeria

Multiple-factor analysis (Generalized Estimating Equations) was used to investigate the statistical association between several factors used during a 2010-11 baseline survey, and prevalence of Listeria monocytogenes and proportion of samples with counts exceeding 100 cfu/g, in surveyed fish and meat products.

EFSA said using the survey‘s data for multiple-factor analysis created issues of sparseness, because of the large number of factors and small number of surveyed RTE food samples that were L. monocytogenes positive or that had a count exceeding 100 cfu/g.

The objective was to get valid EU-level estimates of prevalence and contamination levels in the surveyed RTE foods​, by collecting and using comparable data from Member States.

The survey on Listeria monocytogenes in 2010 and 2011 estimated the European Union-level prevalence in certain RTE foods at retail. EFSA published the first part of its analysis last year​.

Packaged (not frozen) hot or cold smoked or gravad fish, soft or semi-soft cheeses (excluding fresh) and packaged heat-treated meat products were sampled in 26 European Union Member States and Norway.

Two fish product samples from the same batch were analysed at the laboratory and at the end of shelf-life, the meat products and the cheese samples were analysed at the end of shelf-life.

Listeria presence​

The odds of Listeria monocytogenes presence were higher for ‘cold smoked fish‘  than for ‘hot smoked fish‘ and ‘unknown smoked fish‘, for ‘sliced‘ than for ‘not sliced‘ samples and for those with ‘two or more antimicrobial preservatives and/or acidity regulators‘, than for samples with ‘no reported antimicrobial preservatives and/or acidity regulators‘.

For packaged (not frozen) hot or cold smoked or gravad fish samples, the proportion of samples with Listeria monocytogenes counts exceeding 100 cfu/g was associated with ‘possible slicing‘; as ‘sliced‘ fish samples had higher odds of containing the pathogen in excess of 100 cfu/g than ‘not sliced‘ samples.

Higher odds of Listeria monocytogenes presence were found for ‘pâté‘ than for ‘cold, cooked meat products‘ and for ‘sliced‘ samples than for ‘not sliced‘ samples.

For packaged heat-treated meat products, the proportion of samples with counts exceeding 100 cfu/g was associated with the ‘animal species of the origin of the meat product‘ (higher odds for products made from meat from ‘avian species‘ and with ‘remaining shelf-life‘.

No analysis is presented for cheese samples due to the small number of contaminated samples.

Multiple-factor models were constructed for smoked or gravad fish samples at time of sampling and at the end of shelf-life and for packaged heat-treated meat products at the end of shelf-life.

It was not designed to examine the general exposure of EU consumers to L. monocytogenesin food, but targeted RTE food products shown to be at risk of contamination at levels considered to be a public health risk.

Listeria prevalence in RTE foods​

True prevalence of L. monocytogenes in RTE food products depends on the contamination level of the raw material, the processing conditions (i.e. smoking conditions) and the opportunities for cross-contamination (i.e. during slicing).

However, estimated prevalence at retail is indirectly affected by other factors which determine pathogen growth during storage, such as physicochemical characteristics of the product (i.e. pH, aw, presence and concentration of antimicrobials), packaging atmosphere, the storage temperature and storage time.

“Food business operators producing cold smoked fish, pâté or sliced ready-to-eat smoked or gravad fish and heat-treated meat products might actively reconsider food safety management systems and their ongoing verification, in particular with increased attention to environmental L. monocytogenes sampling in the area of the slicing process, in order to ensure effective control of L. monocytogenes in their products,”​ according to one recommendation from EFSA’s scientific report.