UK E. coli O157 outbreak associated with soil on vegetables
30 September 2011
Consumers are reminded to thoroughly wash vegetables and observe good kitchen hygiene following an investigation into 250 cases of gastrointestinal illness caused by an unusual strain of E. coli O157. The investigation into the outbreak, which is now over, revealed an association between illness and handling certain loose raw vegetables in the home, which, although safe to eat, could have had soil on them containing harmful bacteria. Handling raw vegetables in the home explained many, but not all, of the cases
Dr Bob Adak, a gastrointestinal disease expert at the HPA and head of the multi-agency Outbreak Control Team said, "Our study showed a statistically significant association with raw loose leeks and potatoes from sacks but these vegetables may not be the only source of contamination. We also want to stress that it is safe to eat these vegetables as long as they have been stored correctly, thoroughly washed before cooking and good kitchen hygiene practices are followed.
"In this outbreak, which is now over, the vegetables could have carried traces of contaminated soil. It is possible people caught the infection from cross contamination in storage, inadequate washing of loose vegetables, insufficient hand washing after handling the vegetables or by failing to thoroughly clean kitchen equipment, utensils or surfaces after preparing the vegetables."
Between December 2010 and July 2011, the Health Protection Agency (HPA), Health Protection Scotland and Public Health Wales received reports of 250 cases of infection with a particular subtype of E. coli.O157 known as Phage Type 8 (PT8) distributed across England, Scotland and Wales. The majority of these cases were mild to moderate but 74 people were assessed in hospital. Four developed Haemolytic Uraemic Syndrome (HUS) and one patient with underlying health problems died. No cases were reported in Northern Ireland and the outbreak is now over.
This outbreak was not related to the outbreaks in Germany or France earlier this year which were caused by a different strain of E. coli called O104.
Extensive investigations conducted by the multi-agency Outbreak Control Team found that people who were ill with this particular strain of E. coli O157 infection were statistically more likely to have lived in a household where leeks sold loose (i.e. not prepacked) and potatoes bought in or sold from sacks had been handled, than those who had not. There was no evidence to suggest any particular retail source or variety of the produce was responsible for people becoming ill. Illness appears to have been caused by traces of soil carrying the E. coli O157 bacteria present on the vegetables.
Dr Andrew Wadge, Chief Scientist at the Food Standards Agency said: "It's sadly a myth that a little bit of dirt doesn't do you any harm; soil can sometimes carry harmful bacteria and, although food producers have good systems in place to clean vegetables, the risk can never be entirely eliminated. Control of infection from E. coli O157 relies on an awareness of all potential sources of the bacteria and high standards of hygiene where it may be present.
"This outbreak is a timely reminder that it is essential to wash all fruits and vegetables, including salad, before you eat them, unless they are labelled 'ready to eat', to ensure that they are clean. It is also important to wash hands thoroughly as well as clean chopping boards, knives and other utensils after preparing vegetables to prevent cross contamination."
Dr Adak from HPA, added: "It's important to remember that the risk of contracting E. coli O157 in these circumstances is very small compared with the huge benefit of eating plenty of vegetables. But E. coli O157 is a serious infection that can cause significant harm, and the public can protect themselves by taking simple but essential precautions such as preparing raw vegetables safely.
"As soon as the HPA, Health Protection Scotland and Public Health Wales saw an increase in this type of E. coli O157 we began an investigation to find the cause of the outbreak. The multi-agency Outbreak Control Team, which included colleagues at the Food Standards Agency, worked together to find out how people were becoming infected so that action could be taken.
"Now that we have established a statistically significant association with the handling of certain loose vegetables, it warrants us sharing these findings with the public, to enable them to take the necessary steps to minimise their risk of food poisoning.
"Eating five portions of fruit or vegetables daily is a crucial part of a healthy balanced diet, which leads to a longer and healthier life. The HPA and the other agencies involved in this outbreak investigation are committed to encouraging the uptake of five portions of fruit and vegetables a day to help people maintain a healthy weight and lower their risk of serious health problems."
The following Food Standards Agency advice applies to all food preparation and will also help reduce the risk of infection:
- Remove any loose soil before storing vegetables and salads to avoid cross contamination of clean items.
- Thoroughly wash all vegetables (including salads) that will be eaten raw unless they have been pre-prepared and are specifically labelled 'ready to eat'.
- Do not prepare raw vegetables with utensils that have also been used for raw meat.
- Keep raw meat and unwashed vegetables away from ready-to-eat foods during storage and preparation.
- Use different chopping boards, knives and utensils for raw and ready-to-eat foods, or ensure they are washed thoroughly between uses.
- Wash your hands thoroughly after handling raw food - including meat and unwashed vegetables. Always wash your hands thoroughly before preparing food, particularly after using the toilet (or helping others including changing nappies), before meals, and after contact with animals or their environments.
- Cook all minced meat products (i.e. burgers, meatloaf, meat balls etc.) thoroughly, until steaming hot throughout and no pinkness or red meat is visible when you cut into them.
- Ensure that refrigerators are working correctly - bacteria grow more quickly at temperatures over 4oC.
- Only leave cooked foods, meat and dairy products out at room temperature for a short time.
- Store uncooked meats below cooked meats, salad, fruit or vegetables that might be eaten raw to avoid dripping meat juices onto ready to eat food.
- Store uncooked and cooked meats on different plates. Avoid all contact between raw and cooked meats.
- Children and the elderly, who are particularly susceptible to the severe effects of food poisoning, should avoid eating or drinking unpasteurised milk or dairy products.
- People who have been ill should not prepare food for others for at least 48 hours after they have recovered.
Notes to Editors:
- The fact that there was an outbreak of undetermined cause has been in the public domain since February, when an article was published in our weekly Health Protection Report and in subsequent monthly references to case numbers (see http://www.hpa.org.uk/hpr/archives/2011/news0611.htm#vtec). In addition the outbreak was referred to in reports to the public sessions of the HPA Board in March and May this year as well as in a number of Health Protection Scotland's weekly reports. All of this information is publicly available on the HPA and Health Protection Scotland websites.
- People usually become unwell with E. coli O157 infection after eating food or drinking water that is contaminated with the faeces from infected animals, or from contact with farm animals or their environments. E. coli is a common bacterium that can live harmlessly in the gut of animals and people. However, some E. coli bacteria produce toxins that are harmful to people and one of these is a group called vero cytotoxin-producing E. coli or VTEC. The type seen in this outbreak (which is now over), VTEC O157 PT8, is a subset of this group. For more information on E. coli, visit: <>http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/EscherichiaColi/
- The cause of this outbreak was not immediately obvious and over the first six months of this year a series of comprehensive investigations have been carried out by the HPA, Health Protection Scotland and Public Health Wales in an effort to discover how the disease was spread. This involved preliminary interviews with every identified case, followed by further in-depth interviews (of two hours or more) in the homes of a number of cases. Complete histories were taken from each of these patients to find out if the affected people could be linked by common shopping, eating, cooking, recreational or working habits or practices.
- Statistical analysis of information from 30 cases and 62 controls (healthy people who were not ill with this infection) was undertaken and the final analysis indicated that people who were unwell were forty times more likely to have been in a household where people handled leeks sold loose (i.e. not prepacked) than the control group and were twelve times more likely to have been in a household where people handled potatoes bought in or sold from sacks.
- The number of E. coli O157 PT8 cases in this outbreak compares with an average of 81 cases of this type seen across the UK in each of the previous three years.
- Of the 250 cases reported in this outbreak across the UK, 193 were reported in England (and distributed across all regions), 44 cases were reported in Scotland and 14 in Wales. Forty per cent of cases are under 16 and 69 per cent are female.
- Vegetables and salad items might have soil on them. Contaminated soil from one item may also cross-contaminate another item during storage. This is why the public are being advised to wash all vegetables and salad thoroughly prior to cooking or eating. Although the chances are small that any soil on this produce may be contaminated with E. coli O157, this advice is being issued because the organism has the potential to cause serious illness, which can be prevented if these simple steps are taken.
- More information on food safety can be found on the NHS Choices website: http://www.nhs.uk/Livewell/homehygiene/Pages/Foodhygiene.aspx
- The Health Protection Agency is an independent UK organisation that was set up by the government in 2003 to protect the public from threats to their health from infectious diseases and environmental hazards. In April 2013, subject to the usual approvals procedures for establishing new bodies, the Health Protection Agency will become part of a new organisation called Public Health England, an executive agency of the Department of Health. To find out more, visit our website: www.hpa.org.uk
- For more information please contact the national HPA press office at Colindale on 0208 327 7901 or email firstname.lastname@example.org. Out of hours the duty press officer can be contacted on 0208 200 4400.
Updated 03 Oct 2011 to add link to Health Protection Report.
Last reviewed: 18 October 2011