 |  | Fact sheet No 125: Escherichia Coli O157:H7 - July 1996 (WHO, 1996, 4 p.) | ||
 |  | Escherichia Coli O157:H7 | ||
|  | 1. What is Escherichia coli O157:H7? | ||
| | 2. What illnesses does E. coli O157:H7 cause? | ||
| | 3. Sources of infection | ||
| | 4. Control and Prevention Methods | ||
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Escherichia coli is a bacterium that is a common inhabitant of the gut of warm blooded animals, including man. Most strains of E.coli are harmless, however, some strains, such as E. coli O157:H7, can cause severe foodborne disease and are referred to as enterohaemorrhagic E .coli (EHEC). This pathogen produces toxins, known as verotoxins or Shiga-like toxins because of their similarity to the toxins produced by Shigella dysenteriae. The organism can grow from around 7-10C to 50C, with an optimum temperature of 37C. Some EHEC can grow in acidic foods, down to a pH of 4.4, and in foods with a minimum water activity (Aw) of 0.95. It is destroyed by thorough cooking of foods until all parts reach a temperature of 70C or higher. The designation “O157:H7” in the name of this bacterium refers to specific chemical compounds that are found on its surface that distinguishes it from other strains of E. coli.
Symptoms of the illness caused by E.coli O157:H7 include abdominal cramps and watery diarrhoea that can develop into bloody diarrhoea (haemorrhagic colitis ). Fever and vomiting may also occur and most patients recover within 10 days. However, in a small proportion of patients, particularly young children and the elderly, the infection can result in life-threatening complications, such as haemolytic uraemic syndrome (HUS), for example.
HUS is characterized by acute renal failure, haemolytic anaemia and thrombocytopenia. It is estimated that up to 10% of patients with EHEC infection may develop HUS, with a case-fatality rate ranging from 3% to 5%. The incubation period for the illness can range from 3 to 8 days, with a median of 3-4 days.
The reservoir of this pathogen appears to be mainly cattle. It is transmitted to man principally through consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk. Faecal contamination of water and other foods, as well as cross-contamination during food preparation will also lead to infection. Examples of foods implicated in outbreaks of E. coli O157:H7 include hamburgers, fresh-pressed apple cider, yogurt, cheese, dried cured salami, and cooked maize. EHEC can survive and grow on salad vegetables.
Waterborne transmission has been reported, both from contaminated drinking water and from recreational waters. Person-to-person contact is an important mode of transmission through the oral-faecal route. An asymptomatic carrier state has been reported, where individuals show no clinical signs of disease but are capable of infecting others. The duration of excretion of EHEC is about one week or less in adults, but can be longer in children
The prevention of infection requires control measures at all stages of the food chain, from agricultural production on the farm, to processing, manufacturing and preparation of foods in both commercial establishments and the domestic environment.
There are insufficient data to recommend specific intervention methods on the farm in order to reduce the incidence of EHEC in cattle. Good hygienic slaughtering practices will reduce contamination of carcasses by faeces but will not guarantee the absence of EHEC from products. Education in hygienic handling of foods for abattoir workers and those involved in the production of raw meat is essential to keep microbiological contamination to a minimum. Similarly, prevention of contamination of raw milk on the farm is virtually not feasible but education of farm workers in principles of good hygienic practice is necessary in order to keep contamination to a minimum. The only effective method of eliminating EHEC from foods is to introduce a bactericidal treatment, such as heating (e.g. cooking or pasteurization) or irradiation.
Preventive measures for of E.coli O157:H7 infection are similar to other foodborne diseases. However, some of the measures may need to be reinforced for this infection, particularly because of the importance of EHEC infection in vulnerable groups such as children and elderly.
Recommendations to the public and travellers
· Make sure your food, particularly foods made with ground beef (e.g. hamburger) are properly cooked and are still hot when served;· Avoid raw milk and products made from raw milk. Drink only pasteurized or boiled milk;
· Wash hands thoroughly and frequently using soap, in particular after having been to the toilet, or after contact with farm animals;
· Wash fruits and vegetables carefully, particularly if they are eaten raw. If possible, vegetables and fruits should be peeled;
· When the safety of drinking water is doubtful, boil it or if this is not possible, disinfect it with a reliable, slow release disinfectant agent. These are usually available at pharmacies.
A WHO Guide on Safe Food for Travellers is available from the Sales and Distribution Office, Geneva, Switzerland, that gives practical advice for safeguarding health when travelling.
Recommendations to professional and domestic food handlers:
· As food handlers, you should be vigilant during the preparation of food and observe hygienic rules of food preparation (see the attached WHO Golden Rules for Safe Food Preparation).· Professional food handlers who suffer from a foodborne illness, including E.coli O157 infection, should report to their employer immediately.
More information for food handlers is given in the WHO Guide on Hygiene in Food Service and Mass Cartering Establishments.
Further information of Food Safety can be obtained at the WHO WWW Site (http:/www.who.ch/programmes/fnu/fos/gldnrls.htm) or E-mail at foodsafety@who.ch.
For further information please contact Valery Abramov, Health Communications and Public Relations, WHO, Geneva. Tel. (41 22) 791 2543, or Fax (41 22) 791 4858.
All WHO press releases, fact sheets and features are available on the Internet on the WHO Home Page http:www.who.ch/
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