Enterohaemorrhagic Escherichia coli in Food
In May 2011, an unusually high number of cases of haemolytic uraemic syndrome (HUS) (A serious complication usually occurs in patients with abnormal breakdown of red blood cell and reduction in platelets for blood clotting. It is associated with severe acute renal failure) and bloody diarrhoea caused by Shiga toxin-producing E. coli (STEC) (also called verocytotoxin-producing E. coli (VTEC)) was observed in Germany , particularly the northern part. Some patients succumbed to the infection. E. coli strains causing these severe illnesses are also called Enterohaemorrhagic E. coli (EHEC). Laboratory investigations showed that the strains causing the outbreak are of serotype O104, but not the predominant serotype of EHEC, i.e. O157. Subsequently, the German authorities identified the same strain from raw sprouts from a household of patients with an EHEC infection. Follow-up investigation by European Centre for Disease Prevention and Control (ECDC) and the European Food Safety Authority (EFSA), showed that the outbreak of EHEC in Germany and France could have come from fenugreek seeds sourced from Egypt .
Shiga toxin-producing E. coli and Enterohaemorrhagic E. coli
- E. coli is part of the common flora found in intestines of animals and humans. Most of which are non-pathogenic, but some E. coli strains are able to cause gastrointestinal illness in humans. These include some strains of VTEC/STEC called EHEC.
- E. coli strains of VTEC are able to produce one or more verocytotoxins (VT) . These toxins are also similar to Shiga toxins of Shigella dysenteriae, a bacterium that causes bloody diarrhoea, and hence, this group of bacteria is also called STEC. Ruminants, especially cattle, are the natural reservoir for STEC. The STEC strains carried by animals are not necessarily pathogenic for humans, but some strains can cause severe infections.
- EHEC is a pathogenic subset of STEC that is able to cause attaching and effacing lesions in the intestinal mucosa and has the capacity to cause haemorrhagic colitis (bloody diarrhoea) and HUS in humans. HUS is a severe complication of EHEC infection and can be fatal after causing kidney damage.
- E. coli O157:H7 is the predominant and most virulent serotype among EHEC. Symptoms of infections caused by E. coli O157:H7 includes severe abdominal pain and watery or bloody diarrhoea. Some patients may also vomit or experience low-grade fever. The illness is usually self-limited and lasts for an average of eight days. Most people recover within seven to ten days, but up to 15% develop HUS. All people are susceptible to infections, but pregnant women, people with compromised immune systems, young children and the elderly are most at risk for developing serious complications.
- There are other non-O157 serogroups that have been associated with occasional outbreaks of human cases or sporadic cases. These include O26, O91, O103, O104, O111, O113, O117, O118, O121, O128 and O145.1
- Comparing to E. coli O157:H7, the non-O157 serogroups are less likely to cause severe illness. Yet, some non-O157 STEC can cause the most severe manifestations of STEC illness, e.g. E. coli O104:H4 outbreak in Germany . On the other hand, the infective dose for E. coli O157:H7 has been reported to be low and may be as few as 10 organisms, while the infective doses for non-O157 STEC are not well described.
- The serotype causing the outbreak in Germany is rarely associated with outbreak. In addition, the age and sex distribution of cases in this outbreak is highly unusual, in which most cases are adults (20 years or older) and mainly women are affected. The reason for these is unclear. However, further investigations of the strain revealed that it lacks some characteristic genes of EHEC, while contains genes of another pathogenic E. coli namely enteroaggregrative E. coli (EAEC). Hence, it is suggested that the strain is actually EAEC acquired the ability to produce Shiga toxins.2 This may explain or provide clues on the unusual epidemiological features and unexpectedly high level of virulence, but more studies on this are needed.
Sources of and Exposure to STEC
- EHEC and other STEC are transmitted through the faecal/oral route and eating contaminated food is a common vehicle of infection, often through contaminated raw or undercooked meat products and fresh produce. Undercooked or raw hamburger (ground beef) has been implicated in many of the documented outbreaks of E. coli O157:H7. Other implicated food in past E. coli O157:H7 outbreaks included alfalfa sprouts, unpasteurised fruit juices, dry-cured salami, lettuce, game meat, and cheese curds. On the other hand, the non-O157 serogroups have also been detected in beef, pork and lamb mince, and unpasteurised milk.
- According to EFSA, there is an increase in recognition of outbreaks of STEC associated with vegetables, in particular contaminated sprouting seeds and green leafy salad, as noted in the scientific literature.3 In some outbreaks, irrigation water and access of farm animals to the immediate environment of fresh-produce are the suspected origin of contamination. Yet, the origin was not identified in most outbreaks. In addition, the contamination can occur in different steps along the food chain.
- Apart from these food or food animals related sources, contact with lakes, ponds, paddling and swimming pools and direct contact with goats, sheep or other ruminants in petting zoos have also been reported as the sources of past E. coli outbreaks.
- Secondary transmission is possible where a person who has the infection can pass it on to someone else through poor hygiene, such as not washing hands after using the toilet and/or before handling food. Person-to-person spread has also been seen in previous outbreaks, for example in institutions.
Prevention of infections
- Measures to prevent EHEC infections are generally similar to those recommended for other food borne disease, including basic food-hygiene practice, as described in five keys to safer food. The main advice is to wash one’s hands after using the toilet and before consuming food; to wash food thoroughly with clean water, especially if it is consumed raw; and to avoid cross-contamination when preparing food.
- To minimise the risk of E. coli O157:H7, ground beef and hamburgers should be cooked thoroughly to the internal core reaching a temperature of 70°C or above for at least 2 minutes.
- Sprouts of any kind are kept in warm and humid conditions to sprout and grow. These conditions are also favourable for the growth of microorganisms, including pathogenic bacteria. Rinsing will not remove bacteria on raw sprouts and hence, it is recommended to cook them thoroughly before consumption.
Advice to the Trade
- Wash hands with soap and water before handling food and after using the toilet.
- Ground beef and hamburgers should be cooked thoroughly to the internal core reaching a temperature of 70°C or above for at least 2 minutes.
- Keep ready-to-eat fresh fruits and vegetables, especially those pre-cut fruits and fresh leafy vegetables for salads, at temperature at 4 ° C or below.
- Suspend from engaging in any food handling work when suffering or suspected to be suffering from an infectious disease or symptoms of illness such as diarrhoea, vomiting, and fever, etc.
Advice to the Consumers
- Wash fruits and vegetables thoroughly before they are used as salad ingredients. However, fresh leafy vegetable products labelled washed and ready-to-eat should not be rewashed.
- Scrub surface of firm produce, such as melons and cucumbers, with a clean produce brush.
- Do not eat undercooked hamburgers, ground beef and other meat products.
- At-risk populations such as children, the elderly, pregnant women, and persons with weakened immune systems, should avoid raw sprouts and unwashed fresh fruits and vegetables, including lettuce/salads.
Risk Assessment Section
Centre for Food Safety
Scheutz F, Moller Nielsen E, Frimodt-Moller J, Boisen N, Morabito S, Tozzoli R, Nataro JP, Caprioli A. Characteristics of the enteroaggregative Shiga toxin/verotoxin-producing
O104:H4 strain causing the outbreak of haemolytic uraemic syndrome in Germany, May to June 2011. Euro Surveill. 2011;16(24):pii=19889. Available online:
European Food Safety Authority; Urgent advice on the public health risk of Shiga-toxin producing Escherichia coli in fresh vegetables. EFSA Journal 2011; 9(6):2274. [50 pp.] doi:10.2903/j.efsa.2011.2274. Available online: