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 causing
disease be 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 diarrhea stools
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 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 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 led 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 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. It has been proven, however
that Anti-Microbes and Microcide kill E.coli and many other pathogens.
It can be used to treat drinking water, on meat or poultry before
cooking, to wash fruits and vegetables, or to treat a condition.
