E. coli O157:H7 was identified for the first time at the CDC in 1975, but it was not until seven years later, in 1982, that E. coli O157:H7 was conclusively determined to be a cause of enteric disease. Following outbreaks of foodborne illness that involved several cases of bloody diarrhea, E. coli O157:H7 was firmly associated with hemorrhagic colitis.
The Centers for Disease Control and Prevention (CDC) estimated in 1999 that 73,000 cases of E. coli O157:H7 occur each year in the United States. Approximately 2,000 people are hospitalized, and 60 people die as a direct result of E. coli O157:H7 infections and complications. The majority of infections are thought to be foodborne-related, although E.coli O157:H7 accounts for less than 1% of all foodborne illness.
E. coli O157:H7 bacteria are believed to mostly live in the intestines of cattle but have also been found in the intestines of chickens, deer, sheep, goats, and pigs. E. coli O157:H7 does not make the animals that carry it ill; the animals are merely the reservoir for the bacteria.
While the majority of foodborne illness outbreaks associated with E. coli O157:H7 have involved ground beef, such outbreaks have also involved unpasteurized apple and orange juice, unpasteurized milk, alfalfa sprouts, and water. An outbreak can also be caused by person-to-person transmission of the bacteria in homes and in settings like daycare centers, hospitals, and nursing homes.
Symptoms of E. coli O157:H7 Infection
E. coli O157:H7 infection is characterized by the sudden onset of abdominal pain and severe cramps, followed within 24 hours by diarrhea. As the disease progresses, the diarrhea becomes watery and then may become grossly bloody – bloody to naked eye. Vomiting can also occur, but there is usually no fever. The incubation period for the disease (the period from ingestion of the bacteria to the start of symptoms) is typically 3 to 9 days, although shorter and longer periods are not that unusual. An incubation period of less than 24 hours would be unusual, however. In most infected individuals, the intestinal illness lasts about a week and resolves without any long-term problems.
Hemolytic Uremic Syndrome (HUS) is a severe, life-threatening complication of an E. coli O157:H7 bacterial infection. Although most people recover from an E. coli O157:H7 infection, about 5-10% of infected individuals goes on to develop HUS. E. coli O157:H7 is responsible for over 90% of the cases of HUS that develop in North America. Some organs appear more susceptible than others to the damage caused by these toxins, possibly due to the presence of increased numbers of toxin-receptors. These organs include the kidney, pancreas, and brain. Visit the Marler Clark sponsored Web site about Hemolytic Uremic Syndrome for more information.
Thrombotic Thrombocytopenic Purpura (TTP) is a clinical syndrome defined by the presence of thrombocytopenia (low blood platelet counts) and microangiopathic hemolytic anemia. This has generally been recognized as “adult HUS.” There are many possible causes, including E. coli O157:H7, all of which act through the common mechanism of inducing endothelial cell damage. The damage triggers a cascade of biochemical events that ultimately leads to the characteristic feature of TTP – widespread dissemination of hyaline thrombi, composed predominantly of platelets and fibrin, which block the terminal arterioles and capillaries (microcirculation) of most of the major body organs, commonly, the heart, brain, kidneys, pancreas and adrenals. Other organs are involved to a lesser degree. The pathophysiology of this disease results in multisystem abnormalities and the clinical manifestations of the syndrome.
Detection and treatment of E. coli O157:H7
Infection with E. coli O157:H7 is usually confirmed by detecting the bacteria in the stool of the infected individual. Antibiotics do not improve the illness, and some medical researchers believe that medications can increase the risk of complications. Therefore, apart from good supportive care, such as close attention to hydration and nutrition, there is no specific therapy for E. coli O157:H7 infection. The recent finding that a toxin produced by E. coli O157:H7 initially greatly speeds up blood coagulation may lead to medical therapies in the future that could forestall the most serious consequences. Most individuals recover within two weeks.
Preventing E. coli O157:H7 Infection
Eating undercooked ground beef is the most important risk factor for acquiring E. coli O157:H7. Cook all ground beef and hamburger thoroughly. Because ground beef can turn brown before disease causing bacteria are killed, use a digital instant read meat thermometer to ensure thorough cooking. Hamburgers should be cooked until a thermometer inserted into several parts of the patty, including the thickest part, reads at least 160? F. Persons who cook ground beef without using a thermometer can decrease their risk of illness by not eating ground beef patties that are still pink in the middle. If you are served an undercooked hamburger or other ground beef product in a restaurant, send it back for further cooking.
Avoid spreading harmful bacteria in your kitchen. Keep raw meat separate from ready-to-eat foods. Wash hands, counters, and utensils with hot soapy water after they touch raw meat. Never place cooked hamburgers or ground beef on the unwashed plate that held raw patties. Wash meat thermometers in between tests of patties that require further cooking.
Drink only pasteurized milk, juice, or cider. Commercial juice with an extended shelf life that is sold at room temperature (such as juice in cardboard boxes or vacuum-sealed juice in glass containers) has been pasteurized, although this is generally not indicated on the label. Most juice concentrates are also heated sufficiently to kill pathogens.
Wash fruits and vegetables thoroughly, especially those that will not be cooked. Children younger than 5 years of age, immunocompromised persons, and the elderly should avoid eating alfalfa sprouts until their safety can be assured. Methods to decontaminate alfalfa seeds and sprouts are being investigated.
Drink municipal water that has been treated with chlorine or other effective disinfectants, or bottled water that has be sterilized with ozone or reverse osmosis (almost all major brands use one or the other method).
Avoid swallowing lake or pool water while swimming, especially pool water in public swimming facilities.
Avoid petting zoos and other animal exhibits unless there are good hand washing facilities available and other sanitation measures have been taken. Wash your hands and your children’s hands after handling animals.
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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