Opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) on defining pathogenic strains of Shiga toxin‐producing Escherichia coli

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ABSTRACT Shiga toxin‐producing Escherichia coli (STEC) are pathogenic E. coli strains that have been associated with a wide range of human clinical illness ranging from mild diarrhoea to bloody diarrhoea (BD) and haemolytic uremic syndrome (HUS). In its opinion of 18 May 2017, the French Agency for Food, Environmental and Occupational Health and Safety (ANSES) defined the pathogenic STEC strains according to genetic criteria (presence of stx1 and/or stx2, eae or (aaiC and aggR) genes) and serotyping. The list of high risk strains included those belonging to the following serotypes: O157:H7, O26:H11, O145:H28, O103:H2, O111:H8, O104:H4, O80:H2). In 2018, an FAO/WHO expert group proposed to classify STEC strains according to their potential risk of causing severe illness into five risk levels based on virulence gene combinations. In 2020, the EFSA BIOHAZ Panel concluded that all STEC strains are pathogenic to humans, capable of causing at least diarrhoea and that all STEC subtypes may be associated with severe illness. The French Directorate‐General for Food requested ANSES to review the definition of STEC pathogenic strains proposed in the May 2017 opinion in the light of the EFSA BIOHAZ Panel opinion, the FAO/WHO report and recent French and European epidemiological data. A literature review was conducted to collect scientific publications, reports and official documents published between 2017 and 2021. The following data were considered: French data on human cases (incidence, microbiological characteristics of the strains associated with human cases), data from the European surveillance system (ECDC TESSy database), data on the occurrence of STEC in foods. The classifications of STEC strains proposed by ANSES in 2017 and FAO/WHO in 2018 were compared with French microbiological and epidemiological surveillance data (2017‐2021), to assess their predictive potential. As the existing classifications were not fully consistent with the French surveillance data (2017‐2021), a new classification of STEC strains according to their virulence potential was proposed. This classification takes into account the association of strains with severe forms of infection (mainly HUS, followed by BD). The criterion used to rank and classify strains is the positive predictive value (PPV; i.e. the probability of the strain to cause illness) for HUS, then the PPV for BD in case of equivalence. STEC strains with the stx2a and/or stx2d subtypes have the highest potential to cause HUS, particularly in the presence of the eae adhesion gene (group I). eae‐negative strains with the stx2a and/or stx2d variants (group II) also have a high potential to cause HUS, especially in adults (22% of HUS cases in adults compared to 1% in children under 15 years of age). STEC strains with other subtypes of the stx gene (groups III and IV) are less frequently associated with HUS cases and are mainly found in cases of bloody diarrhoea and diarrhoea. Serogroup is no longer used to classify strains. However, serogroup information is still useful in human and food epidemiosurveillance. This classification can be used to define management measures (surveillance, management of contaminated batches) corresponding to the level of protection previously defined by risk managers.

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