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Escherichia coli O157:H7 in Arizona


E. coli O157:H7 is one of several strains of enterohemorrhagic E. coli. Approximately 30-40 cases of E. coli O157:H7 are reported in Arizona each year. Historical data for E. coli infections can be found in the Reports links to the left. In 2006, testing for E. coli changed to include all enterohemorrhagic E. coli, not just O157:H7.  This may have resulted in a small increase in numbers of confirmed cases in 2006.

Recent Outbreaks

E. coli O157 and Ground Beef (October 2007)

In October, 2007, certain frozen ground beef patties were recalled because of possible contamination with E. coli O157:H7.  Testing at state laboratories and CDC identified several cases with similar molecular patterns thought to be associated with the contaminated product.  By the end of the outbreak, 45 cases were identified nationally, with 14 hospitalizations and no known deaths.  Arizona had one case, who was not hospitalized and survived.

E. coli O157 and Spinach (September 2006)

During the fall of 2006, a national outbreak of E. coli O157:H7 in fresh spinach was identified. Eight Arizona cases were involved in the outbreak. The affected product was recalled at that time.

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 ground beef to 160°F to kill E. coli and most other bacteria. Test the meat by putting a food thermometer in the thickest part of the meat. Do not eat ground beef that is still pink in the middle. Keep raw meat separate from ready-to-eat foods.  Color is not a reliable indicator that ground beef patties have been cooked to a temperature high enough to kill harmful bacteria such as E. coli O157:H7. For more information go to
  • 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.
  • To keep your food safe, remember to Clean, Separate, Cook, and Chill. For more food safety information visit and direct questions to and Meat and Poultry Hotline at 1-888-MPHotline (674-6854).

What if I have recalled ground beef in my freezer?

  • Consumers can call the store where the beef was purchased to see if it can be returned OR
  • Discard the ground beef

If you think you are sick with E. coli O157, see your health care provider!

Additional Resources