Monday, May 30, 2011


The ubiquitous Escherichia coli (E.coli) had never posed any danger to humans until new strains were discovered a few years ago with potential to be dangerous to consumers. Interestingly this bug was routinely being tested as a marker for testing foods for possible contamination with fecal matters during production and handling. The group of E.coli coming under the Enterohaemorrhagic (EHEC) category can cause serious food poisoning, if the food is not properly processed to kill them and it is known to cause even death if not immediately treated. One of the most virulent strains under EHEC is the notorious 0157:P7 which was found to be a major culprit in almost all food poisoning cases in the West.

E. coli belongs to bacterial species and it has been found commonly in the gut of humans and warm-blooded animals. Historically most strains of E. coli are harmless. Enterohaemorrhagic E. coli is an exception in that it can cause severe food borne disease. It is transmitted to humans primarily through consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk. Its significance as a public health problem was recognized in 1982, following an outbreak in the United States of America. EHEC produces toxins, known as verotoxins or Shiga-like toxins because of their similarity to the toxins produced by Shigella dysenteriae. EHEC has the amazing capacity to grow in a wide range of temperatures from from 7°C to 50°C, with the optimum temperature being 37°C. Some EHEC can grow in even in acidic foods, with pH as low as 4.4 and in foods with a minimum water activity (Aw) of 0.95. It can be destroyed completely by adequate cooking of foods to ensure that all parts reach a temperature of 70°C or higher. E. coli O157:H7 is the most important EHEC serotype in relation to public health, though other serotypes are also emerging causing occasional outbreaks.

Symptoms of the diseases caused by EHEC may include abdominal cramps, diarrhea, fever and vomitting. It may take any where from three to eight days for the bacteria to be fully incubated and act in human body though most cases can be diagnosed within three to four days. When properly treated the affected person can recover within 7-10 days, though in a few cases, especially when young children and old people are affected the infection can be life-threatening. Haemolytic uraemic syndrome (HUS) one of the diseases caused by this bug is characterized by acute renal failure, haemolytic anaemia and thrombocytopenia. It is believed that up to 10% of patients with EHEC infection may develop HUS, with a fatality rate ranging from 3% to 5%. It can cause neurological complications including seizure, stroke and coma in about 25% of HUS patients and chronic renal sequelae in around 50% of survivors. Some of the outbreaks due to EHEC have involved a high number of cases, such as in Japan in 1996, where an outbreak linked to contaminated radish sprouts in school lunches affected thousands of children. Data on the situation in most developing countries are limited, as surveillance for this pathogen is not done routinely and documentation practices are not in vogue.

Why is that EHEC infection is reported more commonly in Western countries and other affluent populations where hygiene and sanitation awareness is very high? Why is that this infection does not affect people in countries like India where food crops are cultivated in rural areas where open defecation is practiced with high probability of the crop getting contaminate? Probably because Indians consume almost all their foods in overcooked conditions while the salad eating practice based on raw vegetables is prevalent in the West.The serotype O157:H7 which has been studied extensively, is easily differentiated biochemically from other E. coli strains. Interestingly this bug is present in great numbers in cattle and other ruminants such as camels and is transmitted to humans primarily through consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk.

Fecal contamination of water and other foods, as well as cross-contamination during food preparation containing beef and other meat products, contaminated surfaces and kitchen utensils, will also lead to infection. Examples of foods implicated in outbreaks of E. coli O157:H7 include undercooked hamburgers, dried cured salami, unpasteurized fresh-pressed apple cider, yogurt, cheese and milk. What is worrying the food safety experts is that increasing number of outbreaks are now being associated with the consumption of fresh horticultural produce like sprouts, lettuce, coleslaw, tomato, cucumbers, salad etc, which are eaten raw without thermal processing. Possibly these fresh produce materials are contaminated due to contact with feces from domestic or wild animals at some stage during cultivation, handling and storage.

EHEC has also been isolated from bodies of water (ponds, streams), wells and water troughs, and has been found to survive for months in manure and water-trough sediments. Waterborne transmission has been reported, both from contaminated drinking-water and from recreational waters. Organic foods which are produced using natural manure can be most vulnerable to infection by EHEC. Person-to-person contact is an important mode of transmission through the oral-fecal route. There are also instances where infected individuals show no clinical signs of disease but pass on the infection to others. The duration of excretion of EHEC from the body is about one week or less in adults, but can be longer in children. Visiting farms and other venues where the general public might come into direct contact with farm animals has also been identified as an important risk factor for EHEC infection.

The most recent episode of EHEC food poisoning comes from Austria where many consumers were infected by consuming organically grown vegetables from Spain and that country's food safety agency has cautioned the consumers about the dangers of consuming these tainted fresh produce, advising them further to destroy such dangerous bacteria containing products. Some of the vegetables under the scanner include cucumbers, tomatoes and aubergines. There are reported to be 10 casualties in Germany due to this episode and other member countries of EU are gearing up to tackle this contingency without causing major damage to their citizens. The classical belief that only animal products are contaminated by EHEC needs to be reexamined in the context of such episodes involving fruits and vegetables. Probably predominantly meat consuming countries are vulnerable because of improper management of production farms due to shortage of personnel and over mechanization of many operations. Though meat products are segregated during storage, distribution and retailing there can be cross contamination from these foods affecting fresh produce like fruits and vegetables.


No comments: