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. Renal sequelae potentially resulting in chronic kidney failure several years after an HUS episode are also common.
EHEC can be responsible for severe cases of foodborne infection. The first EHEC strain was isolated during a foodborne outbreak in the United States in 1982. 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.
In 1996, Japan experienced a major foodborne outbreak 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 originated in Germany, European health authorities had recorded several thousand cases of food poisoning and 50 deaths . Fenugreek sprouts were the source of this European outbreak.
The incidence of infection with EHEC varies depending on age. It is highest in children under the age of three.
In France, national surveillance of these infections was initiated in 1996. It involves surveillance of HUS cases in children aged under 15, and relies on hospital pediatric departments reporting to Santé publique France . In 2019, 71% of these pediatric HUS cases were in children under the age of three. The incidence rate observed in this age bracket (5.8/100,000 population in 2019) was the highest it had been since surveillance was initiated in 1996. Regional disparities are evident in the annual incidence rate. In 2019, the highest regional incidence rates were observed in Corsica (3.9/100,000 population), Auvergne-Rhône-Alpes (3.3/100,000 population) and Occitanie (2.4/100,000 population).
The largest EHEC outbreak observed in France occurred in 2005. It was caused by frozen hamburgers contaminated with EHEC O157:H7. Sixty-nine cases, including 57 children under the age of 13, were identified. In 2018 and 2019, two minor outbreaks (14 to 17 cases) occurred in children under the age of five. Both these outbreaks were linked to consumption of raw (unpasteurized) cheeses contaminated with EHEC O26:H11 .
It is important to note that outbreaks in adults cannot be ruled out. During the European EHEC O104:H4 outbreak of 2011, female adults accounted for 70% of cases. This unusual distribution of cases may be attributed to the nature of the contaminated food (sprouts).
EHEC pathogens are mainly transmitted through the consumption of contaminated food. Since the natural reservoir of EHEC is mainly the digestive tract of cattle, raw or undercooked meat, raw (unpasteurized) dairy products, and occasionally raw vegetable products are the main food products affected. Contamination may also occur during milking or slaughter of such 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, though rare. In most cases, it is observed in a family environment or in the community (nurseries, etc.).
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. However, treatments based on certain antibiotics such as azithromycin, which avoid the release of these toxins, are currently being assessed. Pending these results, the HUS 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 on cattle farms. However, 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 these infections 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 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).