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E. 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.
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.
Drinking unpasteurized milk and swimming in or drinking sewage-contaminated water can also cause infection.
Bacteria in diarrhea stools of infected persons can be passed from one person to another if hygiene or hand washing 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.
Young children typically shed the organism in their feces for a week or two after their illness resolves. Older children rarely carry the organism without symptoms.
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.
Infection with E. coli O157:H7 is diagnosed by detecting the bacterium in the stool. Most laboratories that culture stool do not test for E. coli O157:H7, so it is important to request that the stool specimen be tested on sorbitol-MacConkey (SMAC) agar for this organism. All persons who suddenly have diarrhea with blood should get their stool tested for E. coli O157:H7.
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 it is thought that treatment with some antibiotics may precipitate kidney complications. Antidiarrheal agents, such as loperamide (Imodium), should also be avoided.
Hemolytic uremic syndrome is a life-threatening condition usually treated in an intensive care unit. Blood transfusions and kidney dialysis are often required. With intensive care, the death rate for hemolytic uremic syndrome is 3%-5%.
Persons who only have diarrhea usually recover completely.
About one-third of persons with hemolytic uremic syndrome have abnormal kidney function many years later, and a few require long-term dialysis. Another 8% of persons with hemolytic uremic syndrome have other lifelong complications, such as high blood pressure, seizures, blindness, paralysis, and the effects of having part of their bowel removed.
E. coli O157:H7 will continue to be an important public health concern as long as it contaminates meat. Preventive measures may reduce the number of cattle that carry it and the contamination of meat during slaughter and grinding. Research into such prevention measures is just beginning.
Consumers should only eat ground beef patties that have been cooked to a safe temperature of 160 degrees F, says Bill Schafer, food safety expert with the University of Minnesota Extension Service. Schafer cites information from the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS).
When a ground beef patty is cooked to 160 degrees F throughout, it can be safe and juicy, regardless of color. "Use an accurate thermometer--don't go by the color of the meat," Schafer advises.
The only way to be sure a ground beef patty is cooked to a high enough temperature to kill harmful bacteria that might be present is to use an accurate, digital, instant-read thermometer.
Color isn't a reliable indicator that ground beef patties have been cooked to a temperature high enough to kill harmful bacteria such as E. coli 0157.H7. Eating a pink or red ground beef patty without first verifying a safe temperature of 160 degrees F brings a significant risk factor for food-borne illness.
Thermometer use to ensure proper cooking temperature is especially important for those who cook or serve ground beef patties to people most at risk for food-borne illness. For at-risk people, E. coli 0157:H7, if present, can lead to serious illness or even death. Those most at risk include young children, the elderly and those with compromised immune systems.
--Prevent leaking from any raw meat juices from getting on other foods, either in the grocery cart or at home in the refrigerator.
--Store ground beef in the refrigerator at 40 F or below; cook within 1-2 days or freeze.
--Wash your hands with soap and hot water before and after handling ground beef to make sure you don't spread bacteria.
--Don't reuse any packaging materials.
--Use soap and hot water to wash utensils and surfaces that have come into contact with the raw meat.
--Don't put cooked hamburgers on the same platter that held the raw patties.
Last Updated: Monday, January 26, 2015 12:20 PM