Escherichia coli (E. coli) is an intestinal bacterium that occurs in humans and animals. It is generally harmless and even beneficial. However, some specimens can cause particular illnesses in humans, such as diarrhea or diseases outside the digestive system (e.g. urinary tract infections). Young children, people with immune deficiency and elderly people are particularly prone to infections caused by such pathogenic E. coli.
E. coli is a diverse group of bacteria. Pathogenic variants of E. coli are divided into several types, the so-called pathotypes, on the basis of their virulence factors (in other words, substances secreted by microorganisms that cause disease in humans and/or animals). Six pathotypes are associated with diarrhea and are together referred to as the diarrhea-causing E. coli. These are:
A number of E. coli cause disease in humans through the production of so-called Shiga toxins. These variants are referred to as ‘Shiga toxin-producing E. coli’ or STEC. This pathotype is most often mentioned in connection with food-related infections. Enterohemorrhagic E. coli (EHEC) is an STEC subgroup and can cause mild diarrhea as well as bloody diarrhea.
Infections with the E. coli STEC pathotype frequently involve E. coli O157. A large number of other STEC variants (known as serogroups or seropathotypes) also cause disease in humans. These other serogroups are often collectively referred to as ‘non-O157 STEC’.
The ‘top 5’ serogroups that are often linked to disease are E. coli O157, O26, O103, O111 and O145. Furthermore, a number of other specific specific serogroups (especially E. coli O104, O45, O121 and 0174) appear to have a strong link with serious disorders such as hemolytic uremic syndrome (HUS).
The E. coli types that cause diarrhea in humans are transmitted by contact with contaminated water or food, or by contact with animals or people. It is mainly ruminants like cattle, goats, sheep and deer that are (asymptomatic) carriers of pathogenic E. coli. Infection through direct contact with animals can happen on farms, for example. The risk is particularly high at petting zoos on account of children being prone to such infections. Good hand hygiene is therefore important. In addition, products made from raw milk, as well as raw or undercooked meat products and raw vegetables also present a risk. Surface water can likewise be a source of infection. Human-to-human transmission is a major source of infection in families and children’s nurseries. The infectious dose is very low. It is estimated that just 1 to 10 bacteria are sufficient. So, it is not surprising that these infections can spread quickly.
People of all ages can contract an infection. Very young children and the elderly, as well as people with an immunity deficiency can develop serious signs of illness and also hemolytic uremic syndrome (HUS) more quickly than others. However, people who do not belong to these more susceptible groups can also become seriously ill.
Although pathogenic E. coli usually cause mild diarrhea or urinary tract infections in humans, the level of illness can also be serious in some cases. Apart from mild diarrhea, enterohemorrhagic E. coli (EHEC), a subgroup of STEC, can, for example, also give rise to bloody diarrhea in humans. Complications occur in 2-10% of cases, such as hemolytic uremic syndrome (HUS), which sometimes necessitates kidney dialysis.
The severity of an infection caused by STEC depends on the type of pathogenic substances (virulence factors) that the concerned E. coli variant produces. The main ones are the Shiga toxins (Stx1 en Stx2) and, for example, intimin (eae).
The hemolytic uremic syndrome (HUS) is a complication that can occur with STEC infections. It is caused by the effect of the Shiga toxin on the kidneys, which stops them from working. Most people recover after a few weeks, but others can incur permanent kidney damage or even die from the consequences.
Guidelines for preventing STEC infections:
