Enterohaemorrhagic Escherichia coli (EHEC)

Understanding this bacterium to avoid food poisoning

The bacterium Escherichia coli (E. coli) is naturally present in the digestive microflora of humans and warm-blooded animals. Some strains of E. coli are pathogenic, including enterohaemorrhagic E. coli (EHEC).  In humans, EHEC are responsible for various disorders ranging from mild diarrhoea to more severe illnesses such as haemorrhagic diarrhoea or haemolytic-uraemic syndrome, a severe kidney disorder which occurs mainly in young children. Below is a presentation of this bacterium and of the role ANSES has played in understanding and effectivel fighting it.

Most Escherichia coli strains are harmless to humans. However, some strains are pathogenic because they have acquired virulence genes that confer it with specific properties.  

The infections caused by EHEC are a major public health concern due to the severity of the symptoms that they can generate, with haemolytic-uraemic syndrome being the most common cause of kidney failure in children under three.

Characteristics of EHEC infection

In humans, EHEC are responsible for various conditions ranging from mild diarrhoea to more severe illnesses such as haemorrhagic diarrhoea and two severe kidney disorders: haemolytic uraemic syndrome (HUC), mainly found in young children, and thrombotic microangiopathy (TMA), found in adults.

Just a few of these bacteria may be enough to trigger infection.  EHEC colonise the patient’s digestive tract, producing toxins (Shigatoxins) that cause vascular lesions in the intestine, kidney and brain, manifesting as various clinical signs and renal and neurological complications.

Children under 15 (especially those under 5), as well as the elderly, have a higher probability than average of developing symptomatic or severe forms of the disease.

How are EHEC transmitted?

  • consumption of contaminated foods. The main foods implicated worldwide in outbreaks of EHEC infection are: undercooked ground beef, unpasteurised dairy products, raw vegetables (lettuce, white radish sprouts, sprouted seeds in general), as well as unpasteurised fruit or vegetable juices, and contaminated drinking water;
  • direct contact with infected animals or their droppings;
  • person-to-person transmission.

How can food become contaminated?

The main reservoirs of these bacteria are cattle and sheep. Since these animals may be asymptomatic carriers, they contribute to contamination of the environment through the bacteria in their faeces. 

Contamination of foods of animal origin occurs in meat mainly at the slaughterhouse (during skinning or evisceration), and in milk on dairy farms during milking.

For fresh produce, contamination can occur when manure or effluent from ruminant farms is spread on the soil in which crops are grown, or when contaminated water is used for irrigation.

Drinking water may be contaminated accidentally or if the water purification process is faulty.

Finally, contamination can occur during food preparation, either by contact with contaminated food or due to poor hygiene of food preparers' hands or of the utensils used by them.

What are the best ways to guard against EHEC bacteria?

  • compliance with general good hygiene practices in the kitchen is paramount. It is important to insist on thorough washing of hands after using the toilet, as well as before preparing and eating meals. To prevent cross-contamination between raw and cooked foods, hands should be washed after handling raw meat or vegetables, work surfaces in contact with raw foods should be washed, and cooked meat should not be placed in a dish that previously contained raw meat without first washing the dish (as is frequently the case when preparing a barbecue);
  • thoroughly cook all minced meat or products containing meat consumed by young children and the elderly. Beef burgers should be cooked to an internal temperature of 70°C;
  • raw milk and raw milk cheeses should not be consumed by children under 3 years;
  • vegetables, as well as fruit and herbs, especially those that will be eaten raw, should be thoroughly washed - and peeled if possible - before preparation and consumption.

ANSES’s work on EHEC

Risk assessment

In 2003, the Agency issued its first report summarizing existing knowledge on these bacteria. Since then, it has issued several opinions which describe these highly pathogenic strains and provided a quantitative assessment of the risks of EHEC in minced beef. The Agency has also assessed the impact of prevention and control measures used throughout the food production, distribution and consumption chain (hygiene rules, self-monitoring, consumer practices) on reducing the risk of HUC.

In May and June of 2011, epidemics due to the consumption of sprouted seeds contaminated with E. coli O104:H4 occurred in Germany and France. ANSES issued two opinions which summarize the currently available knowledge on the bacteria responsible for these epidemics, as well as the pertinent epidemiological data and recommendations for investigations into them.

In May 2016, ANSES was also asked by the General Directorate for Food (DGAL) to update the definitions of the EHEC strains most often responsible for severe forms of food poisoning and to assess the effectiveness of the various sampling plans that could be implemented by manufacturers for the self-monitoring of minced beef batches to be placed on the market.

In its opinion of 18 May 2017, the Agency published the following information, conclusions and recommendations:

  • the list of the five most important EHEC serotypes to be monitored in foods remains valid (O157:H7, O26:H11, O103:H2, O145:H28, and O111:H8);
  • ANSES also stressed that O80:H2 is an emergent serotype in France, and recommends that investigations into its source be continued.;
  • modelling studies conducted for this opinion demonstrated that testing for the five major serotypes in all minced beef products on the market, regardless of the sampling plan under consideration, would make it possible to reduce the risk of haemolytic uraemic syndrome through minced beef consumption by a factor of at least ten;
  • these self-monitoring plans should be integrated into the prevention and control of EHEC bacteria throughout the entire food production and distribution chain;
  • finally, it recommends cooking minced beef burgers for young children to an internal temperature of 70° C, as this would significantly reduce risk of EHEC illness.

Detection and screening methods

The Maisons-Alfort Laboratory for Food Safety has been studying these bacteria for many years and is seeking to identify the genetic factors (virulence factors in particular) that allow them to be detected and characterised. On this basis, it has developed molecular biology methods to rapidly detect bacteria in food that are potentially harmful to humans. With regard to the outbreak that occurred in spring 2011, the work conducted in the ANSES Laboratory for Food Safety, and adopted by the European Union Reference Laboratory, led to an emergency protocol being provided for detecting the variant of the EHEC bacterium responsible for this epidemic.