Escherichia coli (E. coli) O157:H7 is a leading cause of food poisoning (or "foodborne illness"). Based on estimates from the Centers for Disease Control and Prevention (CDC), 73,000 cases of infection and 61 deaths occur in the U.S. each year.

E. coli infection often leads to bloody diarrhea, and occasionally to kidney failure. People can become infected with E. coli O157:H7 in a variety of ways. Though most illnesses have been associated with eating undercooked, contaminated ground beef, people have also become ill after eating contaminated bean sprouts or fresh leafy vegetables such as lettuce and spinach. Person-to-person contact in families and child care centers is also a known mode of transmission. Infection can also occur after drinking raw milk and after swimming in or drinking sewage-contaminated water.

Consumers can prevent E. coli O157:H7 infection by thoroughly cooking ground beef, avoiding unpasteurized milk, and by washing hands carefully before preparing or eating food. Fruits and vegetables should be washed well, but washing may not remove all contamination. Public service announcements on television, radio, or in the newspapers will advise you which foods to avoid in the event of an outbreak.

What is Escherichia coli O157:H7?

Escherichia coli (E. coli) O157:H7 is one of hundreds of strains of the bacterium E. coli. Although most strains are harmless, E. coli O157:H7 produces a powerful toxin that can cause severe illness. E. coli O157:H7 has been found in the intestines of healthy cattle, deer, goats, and sheep.

E. coli O157:H7 was first recognized as a cause of illness in 1982. The outbreak was traced to contaminated hamburgers. The combination of letters and numbers in the name of E. coli O157:H7 refers to the specific markers found on its surface that distinguishes it from other types of E. coli.

How is E. coli O157:H7 spread?

E. coli O157:H7 can be found on most cattle farms, as well as petting zoos. E. coli O157:H7 can live in the intestines of healthy cattle, deer, goats, and sheep. Meat can become contaminated during slaughter, and organisms can be accidentally mixed into meat when it is ground. Bacteria present on the cow's udders or on equipment may get into raw milk. In a petting zoo, E. coli O157:H7 can contaminate the ground, railings, feed bins, and fur of the animals.

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. The number of organisms required to cause disease is very small.

Consumption of contaminated sprouts, lettuce, spinach, salami, drinking unpasteurized milk and juice, and swimming in or drinking sewage-contaminated water can also cause infection.

Bacteria in loose stool 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 E. coli O157:H7 in their feces for a week or two after their illness resolves. Older children and adults rarely carry the organism without symptoms.

What illness does E. coli O157:H7 cause?

People generally become ill from E. coli O157:H7 2 to 8 days (average of 3 to 4) after being exposed to the bacteria. E. coli O157:H7 infection often causes severe bloody diarrhea and abdominal cramps. Sometimes it causes non-bloody diarrhea or no symptoms at all. Usually little or no fever is present, and illness resolves in 5 to 10 days.

In children under 5 years of age and in the elderly, the infection can cause a complication called hemolytic uremic syndrome (HUS), in which red blood cells are destroyed and the kidneys fail. Most cases of HUS are caused by E. coli O157:H7.

Diagnosing E. coli O157:H7

Infection with E. coli O157:H7 is diagnosed by detecting the bacterium in the stool. All diarrhea with blood should get their stool tested for E. coli O157:H7.

Treating Illnesses caused by E. coli O157:H7

Most people recover without antibiotics or other specific treatment within 5 to 10 days. Antibiotics should not be used to treat this infection. There is no evidence that antibiotics improve the course of disease, and it is thought that treatment with some antibiotics could lead to kidney complications. Antidiarrheal agents, such as Ioperamide (Imodium), should also be avoided.

If a person contracts HUS because of an E. coli O157:H7 infection, treatment in an intensive care unit is required, often along with blood transfusions and kidney dialysis.

Long Term Consequences of E. coli O157:H7 Infection

People who only have diarrhea usually recover completely. A small proportion of people with HUS have immediate complications with lifelong implications, such as blindness, paralysis, persistent kidney failure, and the effects of having part of their bowel removed. Many persons with HUS have mild abnormalities in kidney function many years later.

Preventing E. coli O157:H7 Infection

You can take the following steps to help prevent E. coli O157:H7 infection:

• Cook all ground beef and hamburger thoroughly. Because ground beef can turn brown before disease-causing bacteria are killed, use a digital instant-read thermometer to ensure thorough cooking. Ground beef should be cooked until a thermometer inserted into several parts of the patty, including the thickest part, reads at least 160F. 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. You may want to ask for a new bun and a clean plate, too.

• 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 (e.g. juice in cardboard boxes, vacuum sealed juice in glass containers) has been pasteurized, although this is generally not indicated on the label. Juice concentrates are also heated sufficiently to kill pathogens.

• Wash fruits and vegetables under running water, especially those that will not be cooked. Be aware that bacteria are sticky, so even thorough washing may not remove all contamination. Remove the outer leaves of leafy vegetables. Children under 5 years of age, immunocompromised persons, and the elderly should avoid eating alfalfa sprouts until their safety can be assured. Persons at high risk of complications from foodborne illness may choose to consume cooked vegetables and peeled fruits.

• Drink municipal water that has been treated with chlorine or another effective disinfectant.

• Avoid swallowing lake or pool water while swimming. (For more information, see the CDC Healthy Swimming website.)

• 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.