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Shiga toxin-producing Escherichia coli (STEC) - guide

05 July 2011
by EFSA -- last modified 05 July 2011

EFSA publishes report from its Task Force on the E. coli O104:H4 outbreaks in Germany and France in 2011 and makes further recommendations to protect consumers


1. What is E.coli? What is STEC?

All humans and animals carry the bacteria called Escherichia coli (E.coli) in their intestines – they are part of our normal flora and usually harmless. However, there are certain types of E. coli strains that are a risk to human health including those that are capable of producing toxins. These strains are called STEC/VTEC (shiga toxin or verotoxin-producing E. coli) or EHEC (enterohaemorrhagic E. coli), and their toxins have the potential to cause bloody diarrhoea and Haemolytic Uremic Syndrome (HUS), a serious complication that can be fatal. A virulent, very rare strain of STEC known as O104:H4 has been identified as the source of the current outbreaks in France and Germany.

2. What is Haemolytic Uremic Syndrome (HUS)?

Haemolytic uremic syndrome (HUS) is a serious medical complication that can develop in patients suffering from haemolytic anaemia (caused by the abnormal breakdown of red blood cells) and thrombocytopenia (reduction of platelets needed for blood clotting ) leading to severe, bloody diarrhoea. HUS is associated with severe acute renal failure, often requiring intensive care.

3. How do you become infected?

Transmission of STEC infection mainly occurs through eating or handling contaminated food and contact with infected animals. . A wide variety of food has previously been implicated in outbreaks as sources of infection, including undercooked beef and other meat, unpasteurized milk, a variety of fresh produce (e.g. sprouts, spinach and lettuce), unpasteurized juice and cheese. A very small number of STEC bacteria are sufficient to cause infection in humans. People who are infected can also contaminate food during food handling and preparation. Further person-to-person transmission is possible among close contacts (families, childcare centres, nursing homes, etc)

4. What should you do if you develop diarrhoeal symptoms?
If you develop any diarrhoeal symptoms, and you work in a kitchen that prepares food for the public, you should contact occupational health care and restrain from handling food.

If you develop bloody diarrhoea, you should seek medical care. If you have developed diarrhoeal symptoms, pay careful attention to your hand hygiene and wash your hands with soap and, if possible, warm water and rinse under running potable water immediately after toilet visits and avoid preparing or handling food.

Further information on human infections and treatment: European Centre for Disease Prevention and Control

5. Do we know which foods are responsible for the current outbreak?

The consumption of sprouts is suspected of being the cause of infection in the outbreaks in Germany and France, and identification of the E. coli O104:H4 strain in human cases in both countries supports the link between these two outbreaks. However, STEC E. coli contamination may be difficult to identify in some food products, including seeds, and it is possible that investigators will not find any conclusive microbiological evidence.

6. Which sprouted seeds are affected?

STEC Human cases in France reported having eaten sprouts (fenugreek, mustard and rucola) as part of several dishes offered at a social event on 8 June. Fenugreek seeds imported from Egypt either in 2009 and/or 2010 have been found to be epidemiologically implicated in both the German and the French outbreaks.

There is, however, still much uncertainty about whether this is truly the common cause of all the infections as there are currently no positive bacteriological results. Since seeds sold for sprouting are often sold as seed mixes, cross-contamination during re-packaging cannot be excluded. Therefore, consumers should be advised not to grow their own sprouts and to ensure that all types of sprouts are thoroughly cooked before consumption. This advice will be kept under regular review as more information becomes available from the continuing investigations.

7. What is fenugreek?

 Fenugreek is a legume crop believed to be native to the Mediterranean region but now grown for food and feed purposes in most parts of the world. In Asian cuisine the whole or ground seeds are used as spice, alone or in combination with other spices (for instance in curry). Fresh germinated seeds or sprouts are consumed in salads. The safe handling of seeds at harvest and post-harvest is critical with respect to preventing microbial contamination.

8. Do sprouts in general carry a risk of illness?

Sprouts can carry a risk of food-borne illness. Unlike other fresh produce, seeds and beans need warm and humid conditions to sprout and grow. These sprouting conditions are also ideal for the growth of bacteria such as E. coli.

In food-borne outbreaks associated with sprouts, the seed is typically the source of the bacteria. In mass production, there are a number of approved techniques to kill harmful bacteria that may be present on seeds and even microbiological tests for seeds during sprouting. However, no treatment is guaranteed to eliminate all harmful bacteria.

Based on their assessments, EFSA and ECDC strongly recommend advising consumers not to grow sprouts for their own consumption and not to eat sprouts or sprouted seeds unless they have been cooked thoroughly.

9. What is meant by "thorough cooking" of sprouts?

Avoid eating raw sprouts of any kind (arugula, alfalfa, mung beans/beansprouts, mustard and fenugreek) whether home-grown or commercially sold. Sprouted seeds should only be eaten if they have been cooked thoroughly. E. coli bacteria are killed at a cooking temperature of 70°C. Since it is difficult to measure the temperature of sprouting beans and seeds, it is recommended to cook them thoroughly until they are steaming hot throughout, not just warm.

10. Are home-grown sprouts safer?

No. If just a few harmful bacteria are present in or on the seed, the bacteria can grow to high levels during sprouting regardless of the environment in which they are grown. This is why EFSA and ECDC are also recommending avoiding eating home-grown sprouts.

11. Are certain people at a higher risk for infection?

Children, the elderly, pregnant women, and persons with weakened immune systems should avoid eating raw sprouts of any kind (including alfalfa, clover, radish, and mung bean sprouts). While HUS cases are usually observed in children under 5 years of age, in this outbreak over 85% are adults, with a clear predominance of women (about 70%).

12. What other precautions can be taken?

Sprouts should be consumed as soon as possible within a few days at most. Likewise, equipment that has been used for raw seed handling and sprouting seeds should be cleaned thoroughly after use, ideally at high temperatures. Those serving sprouts, either at home or in restaurants, should ensure that procedures to avoid cross-contamination are closely followed and people handling raw sprouted seeds should wash their hands thoroughly before and after contact with the sprouts.

13. How can the bacteria survive in seeds sold in 2009?

Bacteria can get into sprout seeds through cracks in the shell before the sprouts are grown. Once this occurs, these bacteria are nearly impossible to wash out. If the seeds are dry and completely free of moisture, the bacteria can lie dormant for years, particularly when seeds are stored at low temperatures. Later when the seeds are germinated, the conditions of increased moisture and temperature used by growers are ideal for the growth of bacteria.

14. Are the risks for E. coli contamination the same for sprouts as they are for shoots?

Based on current knowledge we do not know whether the risk of E. coli contamination from young plants, so-called shoots, is any different than from sprouts. Whether or not the plants can be contaminated depends on many factors such as where the plants are grown, how they are watered and fertilised and how they are handled during harvesting and further processing. For more information, see  EFSA's urgent advice on the public health risk of Shiga-toxin producing Escherichia coli in fresh vegetables.

15.How can you avoid getting ill from foods?

Despite the many measures in place, consumers can be exposed to infectious agents through contaminated food, in particular in raw or undercooked foodstuffs. However, there are some simple precautions that can be applied to reduce the risk of getting ill from potentially contaminated food items, animals or another ill person. Consumers can often reduce the risk of becoming ill in the home by following good hand hygiene and food handling practices.

16. What exactly is meant by "good personal hand hygiene"?

Wash your hands properly with soap and, if possible, warm water, rinse carefully and dry using disposable kitchen towel or a textile towel (to be washed regularly at 60°C).

    Before preparing, serving, or eating food
    After using the toilet or changing nappies (diapers)
    After handling raw vegetables, roots or meat
    After contact with farm animals or after visiting a farm
    After any contact with faeces from household pets.

17. How about "food handling practices"?

    Any person with diarrhoea or vomiting should refrain from handling food
    Thorough cooking of vegetables and meat destroys disease causing bacteria and viruses
    Meat, including minced meat, should be thoroughly cooked
    All fruits with skin should be peeled and then rinsed under running potable water
    All vegetables should be washed properly under running potable water, especially those that will not be cooked before consumption
    Peel all root vegetables and rinse them under running potable water
    Avoid cross contamination, i.e. spreading bacteria from a raw food item to a ready-to-eat or cooked food item, by for example, using separate cutting boards for raw meat and cooked meat or fresh vegetables and wash the cutting board with soap in between the handling of raw and ready-to-eat food.

Further information: World Health Organization's "Five keys to safer food"

18. Is it better to avoid eating vegetables until the outbreak is over?

Consumers should not avoid consumption of vegetables as they are important in the daily diet providing many nutritional benefits but as always during preparation, good food hygiene practices should be followed.

Source: European Food Safety Authority

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