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Update on Shiga toxin-producing Escherichia coli (STEC) bacteria

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News of 08/06/2011

8 June 2011

An abnormal increase in cases of haemorrhagic diarrhoea and haemolytic uraemic syndrome (HUS) has been observed in Germany and in certain other European countries. A foodborne bacterium could be the source of these cases. ANSES provides an update below on the current state of knowledge regarding these bacteria and the general precautions to be taken.

STEC or Shiga toxin-producing Escherichia coli (E. coli), are bacteria found in the digestive tract of most warm-blooded animals, including humans. They are also called VTECs (Verotoxin-producing E. coli) because they synthesise a toxin called verotoxin.
This family of bacteria, considered to be emerging pathogens, has been implicated in many foodborne outbreaks since the 1980s. However, not all STEC are pathogenic to humans. Their pathogenicity involves a mosaic of virulence genes that have not yet all been discovered. In addition, not all population groups exhibit the same susceptibility to these bacteria (host susceptibility). Certain population groups, such as the elderly, children and immunosuppressed individuals, for example, are therefore more vulnerable to these bacteria.
Among the STEC, a sub-group called EHEC (enterohaemorrhagic E. coli) are bacteria isolated from humans. The symptoms they cause can vary, depending on the individual, and range from simple diarrhoea to death, as well as haemorrhagic diarrhoea and/or severe kidney damage from a complication known as haemolytic uraemic syndrome (HUS).

Poisoning by STEC

In humans, just a few bacteria may be sufficient to trigger the infection. Three main pathways of exposure are responsible for infection in humans:

  • Ingestion of contaminated foods (animal products as well as raw vegetables). This is the primary route of infection,
  • Consumption of contaminated water,
  • Transmission either through contact with an infected animal or its faeces, or person-to-person.

Various clinical signs can be associated with infection by EHEC: bloody diarrhoea, haemolytic uraemic syndrome (HUS) in children (in approximately 10% of cases) and thrombotic thrombocytopenic purpura (TTP) in adults.
HUS, the leading cause of kidney failure in infants, is responsible for serious renal sequelae in one third of cases and can potentially result in death. Since 1995, in France around a hundred cases of HUS, mainly associated with STEC, have been documented annually in children under the age of 15. The people who are the most prone to infection by these bacteria are usually children under five years of age and elderly people aged over 65.

How can food become contaminated?

A variety of wild animals or livestock can be asymptomatic carriers of STEC and thus contribute to contaminating the environment and in some cases market garden crops. However, the main reservoirs of these bacteria are cattle and sheep.
Contamination of foods of animal origin occurs mainly in the slaughterhouse (during skinning or evisceration of the animals), or when milking livestock in places where standard rules of hygiene are not observed.
Fruit and vegetables may become contaminated during spreading of manure from ruminants in areas near the plants, or when using contaminated irrigation water.
Finally, contamination can occur during food preparation, either by contact with tainted food, or because of poor hygiene with respect to hands or utensils used by the person preparing the meal.

How to guard against these bacteria

Raw vegetables should be washed very thoroughly and raw (i.e. unpasteurised) milk should be boiled before being given to very young children (under age 5).
STEC are also temperature sensitive. Cooking is thus likely to partially or totally destroy any STEC contained in food. Various health and safety authorities recommend maintaining a core temperature of 70°C for two minutes when cooking steak and minced beef. It is therefore recommended that hamburgers, especially those served to young children, be cooked until well-done.

Observing general hygiene practices in the kitchen is essential for preventing cross-contamination between raw and cooked foods. For example, washing hands after handling raw meat or vegetables, washing work surfaces in contact with raw foods, washing a dish that contained raw meat before using it again for cooked meat (which frequently occurs when preparing a barbecue, since the cooked meat is often returned directly to the same dish used to marinate the raw meat).

How is ANSES dealing with these bacteria?

Risk assessment
In 2003, ANSES completed an initial report summarising the knowledge to date about these bacteria. Since that time, the Agency has issued several opinions specifically concerning the definition of pathogenic STEC, particularly the subfamily of EHECs, and methods for detecting these bacteria. It has worked on the quantitative evaluation of risks associated with these pathogens specifically by identifying the data to be collected as a priority in order to improve risk assessment and control of these pathogens in the food chain.
ANSES addressed this theme in the context of an opinion on microbial contamination of meat at the slaughterhouse, providing practical recommendations to operators for controlling bacterial hazards, including STEC.
In France, reuse of treated wastewater (RTW) for the irrigation of crops is regulated by the order dated 2 August 2010. Within this context, the Agency examined the food risk related to use of water having undergone urban wastewater sewage treatment for the irrigation of crops, and is currently extending its examination to the overhead irrigation of treated wastewater. It has also given its opinion on the assessment of risks related to effluents from category 1, 2 and 3 animal by-product processing plants for reuse in the irrigation of food and feed crops.
In addition, the Agency regularly provides expertise regarding guides for good hygiene practice and the application of HACCP principles (food safety and hygiene). These guides (GGHPs) are reference documents that are designed by professionals in their given sectors, continually updated, and to which compliance is voluntary. They aim to help professionals with food safety management and compliance to regulatory obligations. In this context, the Agency provides its opinion on which hazards to select and the effectiveness of given measures for achieving the objectives set down in the regulations.

Screening and detection methods
ANSES's Maisons-Alfort Laboratory for Food Safety is has been studying these bacteria for many years and seeking to identify the genetic factors (especially virulence factors) allowing them to be detected and characterised. On this basis, it is developing molecular biology screening methods for the rapid identification of foodborne bacteria that may be harmful to humans.
The work being done in this laboratory, in support of the investigation that is underway on the current outbreak in Germany, was recently taken up by the Istituto Superiore di Sanità, the European Union Reference Laboratory in Rome, in order to offer a protocol as a matter of urgency for detection of the serogroup incriminated in this outbreak (Serogroup O 104), in food.
Finally, within the framework of inter-agency collaboration, ANSES has also drafted for the European health authorities note to accompany its Opinion of 27 May 2010, in light of the investigations currently underway to determine the vector of the recent outbreak.

Find out more

> Note of 6 june 2011 from ANSES and VetAgro Sup (French Reference Laboratory for STEC) accompanying the Agency Opinion of 27 May 2010, in the framework of the current outbreak observed in Germany (PDF)
> Opinion of 27 May 2010 on the advisability of revising the definition of pathogenic STEC, specified in the Opinion of 15 July 2008
> The microbial hazard data sheet: enterohaemorrhagic Escherichia coli (PDF)
> Avis du 11 janvier 2011 sur la révision de la définition des EHEC majeurs typiques et sur l'appréciation quantitative des risques [Opinion of 11 January 2011 on the revised definition of primary types of EHECs and quantitative risk assessment]
> Opinion of 19 May 2010 on the risk assessment of effluents from processing plants of Category 1, 2 and 3 animal byproducts intended to be reused for the irrigation of food and feed crops
> Avis du 1er décembre 2008 sur les techniques de détection [Opinion of 1 December 2008 on detection techniques]
> Rapport de 2008 « Réutilisation des eaux usées traitées pour l'arrosage et l'irrigation » [2008 report on Reuse of wastewater for watering and irrigation]
> Analyse quantitative du risque d'octobre 2007 sur l'Appréciation quantitative des risques liés à Escherichia coli O157:H7 dans les steaks hachés surgelés consommés en restauration familiale en France par les enfants de moins de 16 ans [Quantitative risk assessment of October 2007 on Quantitative assessment of the risks associated with Escherichia coli O157:H7 in frozen beef burgers consumed at home in France by children under 16 years of age]
> Report: Bilan des connaissances relatives aux Escherichia coli producteurs de shigatoxines (STEC) - [Summary of knowledge about Shiga toxin-producing Escherichia coli] April 2003 (PDF)
> French Institute for Public Health Surveillance (InVS)
> National Centre of Reference for Escherichia coli and Shigella: Pasteur Institute and Laboratory affiliated with the National Centre of Reference (NCR): Department of Microbiology, Robert Debré University Hospital