Profiling E. coli O157:H7 and Other STECs

Escherichia coli O157:H7 and other shiga toxin producing E. coli (STEC) can be found in meat and in a number of different fruits and vegetables, and may cause potentially deadly infections, especially in children and in the elderly. STEC also are referred to as verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC)

Some history

Many decades ago, a run-of-the-mill strain of E. coli acquired the ability to produce a toxin known as stx2 – probably courtesy of a bacteriophage that transported it from a random Shigella microbe. After undergoing mutations that changed its antigenic structure and its ability to ferment certain carbohydrates, our E. coli acquired the capacity to produce a second toxin – stx1 – and shiga toxin-producing E. coli O157:H7 was born.

E. coli O157:H7 was isolated for the first time in 1970, from an Irish piglet that had developed enteritis. Five years later, the microbe was found in the stool of a California woman who was suffering from bloody diarrhea. The first confirmed foodborne disease outbreaks caused by E. coli O157:H7 took place in 1982, among patrons of McDonalds – the first on in Oregon, the second in Michigan.

E. coli O157:H7 is just one of several shiga toxin-producing E. coli strains, known collectively as STEC. Other strains include O104:H4 (the cause of a massive sprout-related outbreak in Germany in 2011), as well as O26, O45, O103, O111, O121, and O145.

What are shiga toxin-producing E. coli (STECs) and what is their natural habitat?

E. coli O157:H7 and other STECs are members of the family Enterobacteriaceae. They are motile, rod-shaped bacteria that are capable of growing either with or without oxygen. STECs are found in the large intestines of many animals, especially in ruminants such as cattle. They are introduced into the soil and surface water through contaminated feces or the use of raw manure as fertilizer.

How is STEC transmitted? What is the incubation period of the infection?

STEC food poisoning results when an individual eats food that is contaminated with the microbe. The infection also can be transmitted secondarily by contact with stool from an infected individual. It takes only 100-200 STEC microbes to cause an infection.The incubation period varies from one to eight days, depending on the dose, and on the susceptibility of the victim.

What are the symptoms of an infection with STEC? How long do they last?

Symptoms of STEC infections include severe – often bloody – diarrhea, abdominal pain, and vomiting. Unless complications arise, symptoms typically last for 5 to 10 days.

What is the prognosis?

STEC infections are self-limiting in most cases involving healthy adults. Young children and some elderly victims are at risk of developing hemolytic uremic syndrome (HUS), a severe and sometimes fatal complication. HUS strikes approximately 5-10% of STEC-infected children under the age of 10 years, affecting the function of the kidneys, digestive system and other organs. HUS is fatal in 3 to 5% of cases; 12-30% of HUS victims continue to suffer long-term consequences of their illness, including hypertension or impaired kidney function.

What foods carry STEC?

E. coli O157:H7 and other STEC bacteria can be found most commonly in raw beef, unpasteurized dairy products, and raw produce.

How can people protect themselves from STEC?

People acquire STEC infections by person-to-person transmission; by ingesting contaminated food, milk or water; by coming into contact with infected animals (for example at petting zoos); or by swimming or playing in contaminated water.

The US Centers for Disease Control and Prevention offer these suggestions for avoiding STEC infections:

  1. WASH YOUR HANDS thoroughly after using the bathroom or changing diapers and before preparing or eating food.
  2. WASH YOUR HANDS after contact with animals or their environments (at farms, petting zoos, fairs, even your own backyard).
  3. COOK meats thoroughly. Ground beef and meat that has been needle-tenderized should be cooked to a temperature of at least 160°F/70˚C. It’s best to use a thermometer, as color is not a very reliable indicator of “doneness.”
  4. AVOID raw milk, unpasteurized dairy products, and unpasteurized juices (like fresh apple cider).
  5. AVOID swallowing water when swimming or playing in lakes, ponds, streams, swimming pools, and backyard “kiddie” pools.
  6. PREVENT cross contamination in food preparation areas by thoroughly washing hands, counters, cutting boards, and utensils after they touch raw meat.

Additionally, always pay attention to recall notices, and return any recalled item to the store, or discard it in a sealed bag.

For more information on STECs and other food-borne pathogens, visit the CDC website or read Food Safety: Old Habits, New Perspectives.

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