What is Escherichia coli O157:H7?

How is E. coli O157:H7 spread?

What illness does E. coli O157:H7 cause?

How is E. coli O157:H7 infection diagnosed?

How is the illness treated?

What are the long-term consequences of infection?

What can be done to prevent E. coli O157:H7 infection?

What is Escherichia coli O157:H7?
Escherichia coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless and live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness.

E. coli O157:H7 was first recognized as a cause of illness in 1982 during an outbreak of severe bloody diarrhea; the outbreak was traced to contaminated hamburgers. Since then, most infections have come from eating undercooked ground beef.

The combination of letters and numbers in the name of the bacterium refers to the specific markers found on its surface and distinguishes it from other types of E. coli.

How is E. coli O157:H7 spread?
The organism can be found on a small number of cattle farms and can live in the intestines of healthy cattle. Meat can become contaminated during slaughter, and organisms can be thoroughly mixed into beef when it is ground. Bacteria present on the cow's udders or on equipment may get into raw milk.

Eating meat, especially ground beef, that has not been cooked sufficiently to kill E. coli O157:H7 can cause infection. Contaminated meat looks and smells normal. Although the number of organisms required to cause disease is not known, it is suspected to be very small.

Among other occasional sources of infection are sprouts, lettuce, salami, unpasteurized milk and juice, and swimming in or drinking sewage-contaminated water.

Bacteria in diarrheal stools of infected persons can be passed from one person to another if hygiene or handwashing habits are inadequate.  This is particularly likely among toddlers who are not toilet trained. Family members and playmates of these children are at high risk of becoming infected.

What illness does E. coli O157:H7 cause?
E. coli O157:H7 infection often causes severe bloody diarrhea and abdominal cramps; sometimes the infection causes nonbloody diarrhea or no symptoms. Usually little or no fever is present, and the illness resolves in 5 to 10 days.

In some persons, particularly children under 5 years of age and the elderly, the infection can also cause a complication called hemolytic uremic syndrome, in which the red blood cells are destroyed and the kidneys fail. About 2%-7% of infections lead to this complication. In the United States, hemolytic uremic syndrome is the principal cause of acute kidney failure in children, and most cases of hemolytic uremic syndrome are caused by E. coli O157:H7.

How is E. coli O157:H7 infection diagnosed?
Infection with E. coli O157:H7 is diagnosed by detecting the bacterium in the stool. All persons who suddenly have diarrhea with blood should get their stool tested for E. coli O157:H7.

How is the illness treated?
Most persons recover without antibiotics or other specific treatment in 5-10 days. There is no evidence that antibiotics improve the course of disease, and there is a concern that treatment with antibiotics may lead to kidney complications. Antidiarrheal agents, such as loperamide (Imodium), should also be avoided.

Hemolytic uremic syndrome is a potentially life-threatening. Blood transfusions and kidney dialysis are often required. With intensive care, the death rate for hemolytic uremic syndrome is 3%-5%.

What are the long-term consequences of infection?
Persons who only have diarrhea without HUS usually recover completely.  Patients with HUS can develop to high blood pressure or chronic renal failure. Lethality: The overall mortality rate for E. coli O157:H7 is <1%.  For those who develop HUS, the death rate is between 3-5%.  

What can be done to prevent E. coli O157:H7 infection?

There are several things you can do to reduce your risk of infection:

• Cook all ground beef and hamburger thoroughly.

• Keep raw meat separate from ready-to-eat foods.

• Wash hands, counter tops, and utensils with hot soapy water after they touch raw meat.

• Drink only pasteurized milk, juice, or cider.

• Wash fruits and vegetables thoroughly, especially those that will not be cooked.

• Drink municipal water that has been treated with chlorine or other effective disinfectants.

• Avoid swallowing lake or pool water while swimming.

• Make sure that persons with diarrhea, especially children, wash their hands carefully with soap after bowel movements to reduce the risk of spreading infection, and that persons wash hands after changing soiled diapers.

• Anyone with a diarrheal illness should avoid swimming in public pools or lakes, sharing baths with others, and preparing food for others.

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