Frequently Asked Questions
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
Consumers can prevent E. coli O157:H7 infection by thoroughly
cooking ground beef, avoiding unpasteurized milk, and washing
Because the organism lives in the intestines of healthy cattle,
preventive measures on cattle farms and during meat processing
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.
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
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.
illness does E. coli O157:H7 cause?
E. coli O157:H7 infection often causes severe bloody
diarrhea and abdominal cramps; sometimes the infection causes
non-bloody 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.
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.
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%.
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.
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.
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 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. 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
Drink municipal water
that has been treated with chlorine or other effective disinfectants.
Avoid swallowing lake or pool water while swimming. See
more information about this.
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 more information
about reducing your risk of foodborne illness, visit the US Department
of Agricultures Food Safety and Inspection Service website
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