Escherichia coli O157:H7
Escherichia coli O157:H7 is an emerging
cause of foodborne illness. An estimated 73,000 cases of infection
and 61 deaths occur in the United States each year. Infection often
leads to bloody diarrhea, and occasionally to kidney failure. Most
illness has been associated with eating undercooked, contaminated
ground beef. Person-to-person contact in families and child care
centers is also an important 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 washing hands
carefully.
Because the organism lives in the intestines of healthy cattle,
preventive measures on cattle farms and during meat processing are
beinginvestigated.
What is Escherichia coli
O157:H7?
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.
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 known sources of infection are consumption of 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.
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.
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. 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.
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 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%.
What are the long-term consequences of
infection?
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.
What can be done to prevent the infection?
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.
What can you do to 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 meat 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
160º 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. 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 thoroughly, especially
those that will not be cooked. Children under 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.
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.
For more information about reducing your risk
of foodborne illness, visit the US Department of Agriculture’s
Food Safety and Inspection Service website at: http://www.fsis.usda.gov
or the Partnership for Food Safety Education at: For more advice
on cooking ground beef, visit the U.S. Department of Agriculture
web site at: http://www.fsis.usda.gov/OA/topics/gb.htm
Content Source
Centers for Disease Control and Prevention
http://www.cdc.gov/
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