Closing gaps for performing a risk assessment on Listeria monocytogenes in ready-to-eat (RTE) foods: activity 1, an extensive literature search and study selection with data extraction on L. monocytogenes in a wide range of RTE food

Abstract

The objective of this work is to describe the occurrence and levels of contamination of Listeria monocytogenes in ready-to-eat (RTE) foods (review question 1) and the risk factors of the L. monocytogenes contamination in different RTE foods (review question 2) using an extensive literature search. Literature searches covering the 1990-2015 period resulted in 308 eligible records. Data extraction was carried out using a Distiller SR questionnaire including general information about the study, RTE product (population) and analytical methodology, risk factors (exposure and comparators) and results (outcome) about prevalence and concentration of L. monocytogenes. Up to 778 data were extracted regarding the outcome “prevalence”, mostly from dairy products (N=276), meat products (N=173) and seafood (N=151). Semi-quantitative (N=244) and quantitative (N=14) data on L. monocytogenes concentration was less available. The number of studies not detecting the pathogen was considerable, i.e. the 25th percentile equalled zero in case of meat, dairy, produce and other RTE food categories. For produce, the median value was also zero. In almost all sub-categories, a wide range of prevalence values were recorded. The distribution of the prevalence was asymmetric, with outliers as well as extreme values. The median of the prevalence was below 10% for almost all sub-categories, except for fermented sausages (10%), cold smoked fish (13%), smoked fish (12%) and cured/salted fish (12%). The serotypes 1/2a, 1/2b, 1/2c and 4b were the most reported in the reviewed studies for all food categories, except for produce. The impact of some of the (risk) factors considered in this review was hard to assess, as only few studies dealt with the impact of an intervention on the L. monocytogenes prevalence in naturally exposed RTE foods. Among them, an eradication programme caused a drastic reduction of L. monocytogenes prevalence in the environment and in the RTE product (smoked rainbow trout).