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have decoded the DNA of E. coli O157:H7 (E. Coli). By
documenting the complete genetic code of E. coli O157:H7,
scientists have laid the groundwork for a possible
vaccine that might prevent the disease in cattle, and,
hence, humans. Read about it here.
O157:H7 (E. Coli)
Escherichia coli O157:H7 is an emerging cause of
foodborne illness. An estimated 10,000 to 20,000 cases of
infection 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
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
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.
Drinking unpasteurized milk and swimming in or drinking
sewage-contaminated water can also cause infection.
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.
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
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.
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
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
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
What can you do
to prevent E. coli O157:H7 infection?
Cook all ground beef or hamburger thoroughly. Make sure
that the cooked meat is gray or brown throughout (not
pink), any juices run clear, and the inside is hot.
If you are served an undercooked hamburger in a
restaurant, send it back for further cooking.
Consume only pasteurized milk and milk products. Avoid
Make sure that infected persons,
especially children, wash their hands carefully and
frequently with soap to reduce the risk of spreading the
Drink municipal water that has been treated with adequate
levels of chlorine or other effective disinfectants.
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