This document is based on the conclusions of a study carried out by experts on microbiological risks from the European Food Safety Authority (EFSA) and published in April 2020. The need to carry it out arose from an outbreak of Listeria monocytogenesST6, between the years 2015 and 2018, which affected several countries and caused 53 people sickened and 10 died. The source of infection was some frozen vegetables. Its processing included a previous bleaching in freezing. Bleaching is a procedure that is carried out with hot water or steam in order to stop the enzymatic activity that causes changes in the color, flavor and texture of the food. Environmental contamination from a freezing plant was the origin and reason for the persistence of the strain that caused the outbreak from 2015 to 2018.
EFSA already published in the summer of 2018 recommendations on sampling and microbiological methods to maximize the sensitivity of detection of L. monocytogenes in the processing water and in the environment of the premises that produce frozen fruits, vegetables or herbs. Recommendations were also made on the identification of critical sampling sites to carry out monitoring of the environment of these establishments (ME).
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