Most Escherichia coli (E. coli) are common bacteria which normally inhabit the intestines of animals, including humans and are harmless. Normally these E. coli serve a useful function in the gut by suppressing the growth of other, harmful bacterial species and by synthesizing appreciable amounts of vitamins.
Certain subtypes of E. coli do however cause a range of infections which may affect the intestines or in other parts of the body such as the urinary tract and bloodstream.
One subtype of E. coli called Vero cytotoxin-producing E. coli produces potent toxins and can cause severe disease in man. The most important VTEC E. coli associated with human disease in the UK is the strain E. coli O157 (VTEC O157). This strain is not usually carried by humans, but its main reservoir is the intestines of healthy cattle, sheep or other animals in which it does not usually produce disease.
Please see the section on Escherichia coli (E. coli) for more information about general infections that can be caused by other strains of E. coli.
Who gets it and how serious is it?
Anyone can become infected with E. coli O157 (VTEC O157).
The infectious dose of E. coli O157 appears to be very low, probably less than 100 organisms and the incubation period (between exposure and the occurrence of symptoms) is usually between one and eight days (median 3-4 days), although periods as long as fourteen days have been suggested in certain outbreaks.
Humans become infected through the consumption of contaminated foods, particularly inadequately cooked minced beef (often in the form of beefburgers) and milk (unpasteurised and contaminated post pasteurisation). However, outbreaks have been associated, amongst other things, with yogurt, cooked meats, meat pies, cheese, dry cured salami, raw vegetables, salad vegetables, unpasteurised apple juice and water.
Infection may also be transmitted from person-to-person and from direct contact with animals or contaminated environments. There are risks, especially to children, who visit farm centres. In August and September 2009 an outbreak of Escherichia coli O157 led to severe illness in a number of visitors to Godstone Farm (a petting farm) in Surrey. The report of the independent investigation into the outbreak (The Griffin Report) is available from the investigation website at: www.griffininvestigation.org.uk.
The Health Protection Agency (HPA) updated a leaflet in April 2010 for the public on farm visits and how to reduce the risk of infection with E. coli O157 which is available from: http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1270122184581
The illness can range from mild diarrhoea to bloody diarrhoea (haemorrhagic colitis) and may be accompanied by severe stomach cramps. A severe complication of E. coli O157 infection is haemolytic-uraemic syndrome (HUS) which occurs in up to 10% of patients infected with VTEC O157. It particularly affects young children and the elderly and in a small number of cases, it can be fatal. More information about E. coli O157 (VTEC O157) is available from the HPA website.
Most patients with infections caused by E. coli O157 (VTEC O157) do not require specific treatment and make a full recovery, although the advice of a health professional should be sought in all cases of severe diarrhoea. Oral rehydration therapy maybe advised to prevent dehydration. Antibiotics are generally contra-indicated in the treatment of this infection.
It is estimated that about 30% of patients with E. coli O157 (VTEC O157) will require hospital admission. Patients who develop HUS will require intensive support in hospital.
How common is it?
In Wales during 2009, there were 77 cases reported of E. coli O157 infection. Sources of infection can include consumption of contaminated food or drink, contact with domesticated or farm animals and their faeces and travel abroad.
Large community outbreaks of E. coli O157 (VTEC O157) have been recorded in many countries including Wales. An outbreak of E. coli O157 occurred in September/October 2005 with cases recorded in 44 different schools in the South Wales valleys. In total 157 people, mainly children, fell ill and a five-year old child died.
More information about the surveillance of E. coli O157 infection in Wales is available from the Public Health Wales Health Protection microsite by following the link: rates and surveillance of E. coli O157 in Wales.
Adequate control measures and good hygiene practices are important in the prevention of infections due to E. coli O157, these include:
- Washing hands thoroughly before eating or preparing food, after using the toilet, changing nappies or cleaning up after others with diarrhoea.
- Ensuring meat, especially minced beef, is cooked thoroughly (meat can become contaminated during slaughter, and organisms can be accidentally mixed into meat when it is minced).
- Hygienic handling, preparation and storage of raw meat and other animal products and making sure that raw meats and the implements used to handle them do not come into contact with cooked meat or ready-to-eat food.
- Washing hands thoroughly after contact with domestic or farm animals or soil; this includes during visits to petting farms/zoos as E.coli O157 can contaminate the ground, railings, feed bins, and fur of the animals. Advice for farmers (including a supplement for teachers) on avoiding ill health at open farms has been published by the Health and Safety Executive (HSE) and is available at: http://www.hse.gov.uk/pubns/ais23.pdf
- Peeling raw fruit and vegetables and washing thoroughly before eating and avoiding unpasteurised milk (which can become contaminated from contact with cows udders) and unpasteurised fruit juices.
- Avoiding swallowing water when swimming in untreated or public water facilities.
A factsheet containing advice for people at home and in other environments where someone has E. coli O157 infection has been produced by the HPA and is available from: http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1254510413069
Minimising impact in Wales
Enhanced surveillance of E. coli O157 (VTEC O157) has been undertaken in Wales by Public Health Wales since February 1990. It is one of the most complete surveillance programmes of its type in the world.
This surveillance for E. coli VTEC O157 in Wales provides timely reporting of sporadic cases and enhances detection and containment of outbreaks. It also provides valuable information about E.coli VTEC O157 infections and demonstrates the wide range of associated clinical illness.
CDSC Wales has a downloadable questionnaire for completion by investigators. A copy of the questionnaire should be sent to Communicable Disease Surveillance Centre (CDSC) immediately on completion of the investigation.
Download the Escherichia coli (VTEC) O157 Questionnaire **Updated July 2009**