Pathogen and transmission
Certain strains of the intestinal bacterium Escherichia coli (E. coli), known as enterohaemorrhagic E. coli (EHEC), produce a toxin known as verotoxin. These bacteria are also known as verotoxin-producing E. coli (VTEC). Since the verotoxin is similar to the Shiga toxin, they are sometimes also known as shigatoxin-producing E. coli (STEC).
The natural reservoirs for these bacteria are cattle and other ruminants (such as sheep, goats and deer). EHEC can be present in their intestines (and thus in their faeces) without making the animals sick. The bacteria are transmitted to humans primarily through the consumption of contaminated food (undercooked meat, vegetables, fruit or raw milk products) and drinking water.
The EHEC bacteria can also be transmitted to humans through swimming or bathing in contaminated water or through smear infection – direct contact with the faeces of infected animals or other persons. Among infected humans, the EHEC bacteria are typically excreted over five to 20 days, though this period can also be longer, especially for children. During this time, the infected person can also infect others.
Pathology
Three to four days (sometimes even two to ten days) after infection, diarrhoea and severe stomach cramps can occur. A small number of infected persons may develop a severe form of bloody diarrhoea, sometimes accompanied by fever. This is because the verotoxin produced by the bacteria is attacking the lining of the intestinal wall and the blood vessel walls. Some EHEC infections, however, may develop symptom-free. Infants, small children, older people and persons with weakened immune systems are particularly prone to more severe EHEC development.
One particularly serious form of this is haemolytic uremic syndrome (HUS), in which the kidneys, the blood vessels and the blood cells are attacked. HUS primarily affects children, but its occurrence is rare. Up to five per cent of HUS cases are fatal, despite intensive treatment, and up to 20 per cent of the persons affected can suffer lasting kidney damage.
Treating EHEC with antibiotics is not recommended, because these can make the disease’s progress worse. Thus, treatment is focused on easing the symptoms and their effects.
Distribution and frequency of occurrence
Cases of EHEC are seen and recorded in almost all industrialised countries, and are likely to occur worldwide. Any case of EHEC in Switzerland is subject to mandatory reporting. The Federal Office of Public Health receives up to 1,000 such reports a year.
Prevention
The best ways to avoid EHEC infection are to boil raw milk before consumption and to ensure that all meat is adequately cooked through. Further preventive actions include washing the hands thoroughly with soap and water after every visit to the toilet, before any work in the kitchen, after handling raw meat, before meals and after interacting with animals. The last of these will also help protect children, e.g. after a visit to a petting zoo. To avoid cross-contamination, raw meat and other raw food should not be prepared using the same kitchen utensils or work surfaces unless these are thoroughly cleaned between such uses.