Symptoms of infection
The symptoms associated with EHEC begin 3 to 8 days after infection. They include abdominal pain and diarrhea, which may develop into bloody diarrhea (hemorrhagic colitis). Vomiting and fever may also occur.
At the same time, the toxins produced by EHEC (known as Shiga toxins because they resemble those produced by Shigella dysenteriae or Shiga bacillus) destroy the lining of blood vessels and cause blood clotting problems and high blood pressure. In 10% of infected individuals, the spread of Shiga toxins results in hemolytic uremic syndrome (HUS), which is fatal in 3 to 5% of cases. HUS is characterized by impaired kidney function and a drop in blood cell levels (red blood cells and platelets). A quarter of people with HUS also develop neurological complications that can lead to coma.
EHEC can be responsible for severe cases of foodborne infection. The first epidemiological data were recorded in 1982, when the first strain of EHEC was isolated during an outbreak of food poisoning in the United States. The outbreak was caused by hamburgers containing undercooked meat patties. EHEC has since given rise to several other outbreaks and currently represents a major public health issue. One of the serotypes most frequently responsible for infection is O157:H7.
In 1996, Japan experienced a major outbreak of food poisoning caused by serotype O157:H7. A total of 9,578 cases were reported in individuals who had eaten radish sprouts. In 2011, a strain of EHEC belonging to serotype O104:H4 caused a similar episode in Europe. By the end of the outbreak, which originally began in Germany, European health authorities had recorded several thousand cases of food poisoning and 47 deaths. An inquiry revealed that fenugreek sprouts imported from Egypt were the source of the outbreak.
The incidence of infection with EHEC varies depending on age. It is highest in children under the age of three. However, during the European outbreak that occurred in 2011, 70% of those affected were female adults. This unusual distribution of cases among the population can largely be attributed to different eating habits: women tend to eat more raw vegetables and salad than men, so the impact of the outbreak on women was greater.
The largest recorded outbreak in France occurred in 2005 as a result of frozen hamburgers. The health authorities reported 69 cases, 57 of which were in children under the age of 13.
EHEC pathogens are mainly transmitted through the consumption of contaminated food, usually raw or undercooked meat, raw (unpasteurized) dairy products, and occasionally raw vegetable products. Since the natural reservoir of EHEC is mainly the digestive tract of cattle, contamination may also occur when milking or slaughtering these animals. Fecal matter from ruminants in the earth, in manure or in water (ponds and streams) is another potential source of contamination.
Human-to-human transmission of EHEC is also possible, but it is rare. In most cases, it occurs from children to adults, for example when changing or washing an infant.
Most antibiotics are not recommended for treating EHEC infections. By destroying bacteria, antibiotics trigger the release of Shiga toxins in the body, which can worsen HUS. To avoid this situation, the preferred therapeutic strategy involves repairing the damage caused by Shiga toxins (a fall in red blood cell and platelet count, renal impairment) by transfusion, dialysis and plasma exchange.
Episodes of diarrhea are treated symptomatically: patients are rehydrated but are not given anti-diarrheal drugs to ensure that they eliminate the bacterium and its toxins in stools.
Prevention and recommendations
We do not yet have the knowledge needed to reduce the incidence of EHEC in cattle populations. But tests can be performed to determine whether a given animal carries the bacterium. If necessary, meat can be given bactericidal treatment, which involves heating or irradiation. Although these techniques are useful, they do not systematically guarantee the absence of EHEC in food. Effective prevention of EHEC infection requires the application of strict hygiene practices throughout the entire food chain, from producer to consumer.
People involved in producing and preparing raw vegetable and animal products must be given training in best hygiene practices.
Consumers and cooks can avoid most EHEC infections by adhering to the following recommendations:
- make sure minced beef is cooked right through, especially for children under the age of 5;
- young children and the elderly should avoid raw (unpasteurized) cheeses;
- wash fruit, vegetables and herbs, especially if they are eaten raw;
- wash your hands before preparing meals and as often as necessary;
- make sure cooking implements are kept clean, especially if they have come into contact with raw meat, to avoid cross-contamination;
- keep cooked and raw food separate;
- do not allow very young children (under the age of 5) to come into contact with farm animals, especially cattle, sheep and their environment;
- do not drink water that has not undergone microbiological testing (from a well or spring).
At the Institut Pasteur
The Institut Pasteur houses the National Reference Center (CNR) for Escherichia coli, Shigella and Salmonella. The CNR is hosted by the Enteric Bacterial Pathogens Unit, directed by Dr. François-Xavier Weill.
The CNR is involved in monitoring EHEC infections. Each year, it analyzes, records and classifies the samples it receives from French laboratories (both medical test and hospital laboratories).
The CNR plays a leading role in the event of an outbreak. It alerts the French General Directorate of Health and the National Public Health Agency (Santé publique France) of any reported cases. It contributes to epidemiological investigations by analyzing samples, carrying out molecular typing of bacterial strains and developing new molecular tools to improve monitoring of bacterial strains.
When the EHEC O104:H4 outbreak occurred in Europe in May 2011 as a result of contaminated sprouts, the CNR played a key role in detecting the first cases of infection in France and developing a rapid diagnostic test for infections caused by this serotype.
Surveillance and public health : National Reference Center (CNR) for Escherichia coli, Shigella and Salmonella led by François-Xavier Weill