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What
is Escherichia coli?
Escherichia coli
(abbreviated as E. coli) are a large and diverse group
of bacteria. Although most strains of E. coli are harmless,
others can make you sick. Some kinds of E. coli can cause
diarrhea, while others cause urinary tract infections, respiratory
illness and pneumonia, and other illnesses. Still other kinds
of E. coli are used as markers for water contamination—so
you might hear about E. coli being found in drinking
water, which are not themselves harmful, but indicate the water
is contaminated. It does get a bit confusing—even to microbiologists.
What
are Shiga toxin-producing E. coli?
Some kinds of E.
coli cause disease by making a toxin called Shiga toxin.
The bacteria that make these toxins are called “Shiga toxin-producing”
E. coli, or STEC for short. You might hear them called
verocytotoxic E. coli (VTEC) or enterohemorrhagic E.
coli (EHEC); these all refer generally to the same group
of bacteria. The most commonly identified STEC in North America
is E. coli O157:H7 (often shortened to E. coli
O157 or even just “O157”). When you hear news reports
about outbreaks of “E. coli” infections,
they are usually talking about E. coli O157.
In addition to E.
coli O157, many other kinds (called serogroups) of STEC cause
disease. These other kinds are sometimes called “non-O157
STEC.” E. coli serogroups O26, O111, and O103 are
the non-O157 serogroups that most often cause illness in people
in the United States.
Are
there important differences between E. coli O157 and other
STEC?
Most of what we know
about STEC comes from outbreak investigations and studies of E.
coli O157 infection, which was first identified as a pathogen
in 1982. The non-O157 STEC are not nearly as well understood,
partly because outbreaks due to them are rarely identified. As
a whole, the non-O157 serogroup is less likely to cause severe
illness than E. coli O157; however, some non-O157 STEC
serogroups can cause the most severe manifestations of STEC illness.
Who
gets STEC infections?
People of any age can
become infected. Very young children and the elderly are more
likely to develop severe illness and hemolytic uremic syndrome
(HUS) than others, but even healthy older children and young adults
can become seriously ill.
What
are the symptoms of STEC infections?
The symptoms of STEC
infections vary for each person but often include severe stomach
cramps, diarrhea (often bloody), and vomiting. If there is fever,
it usually is not very high (less than 101˚F/less than 38.5˚C).
Most people get better within 5–7 days. Some infections
are very mild, but others are severe or even life-threatening.
What
are the complications of STEC infections?
Around 5–10%
of those who are diagnosed with STEC infection develop a potentially
life-threatening complication known as hemolytic uremic syndrome
(HUS). Clues that a person is developing HUS include decreased
frequency of urination, feeling very tired, and losing pink color
in cheeks and inside the lower eyelids. Persons with HUS should
be hospitalized because their kidneys may stop working and they
may develop other serious problems. Most persons with HUS recover
within a few weeks, but some suffer permanent damage or die.
How
soon do symptoms appear after exposure?
The time between ingesting
the STEC bacteria and feeling sick is called the “incubation
period.” The incubation period is usually 3-4 days after
the exposure, but may be as short as 1 day or as long as 10 days.
The symptoms often begin slowly with mild belly pain or non-bloody
diarrhea that worsens over several days. HUS, if it occurs, develops
an average 7 days after the first symptoms, when the diarrhea
is improving.
Where
do STEC come from?
STEC live in the guts
of ruminant animals, including cattle, goats, sheep, deer, and
elk. The major source for human illnesses is cattle. STEC that
cause human illness generally do not make animals sick. Other
kinds of animals, including pigs and birds, sometimes pick up
STEC from the environment and may spread it.
How
are these infections spread?
Infections start when
you swallow STEC—in other words, when you get tiny (usually
invisible) amounts of human or animal feces in your mouth. Unfortunately,
this happens more often than we would like to think about. Exposures
that result in illness include consumption of contaminated food,
consumption of unpasteurized (raw) milk, consumption of water
that has not been disinfected, contact with cattle, or contact
with the feces of infected people. Some foods are considered to
carry such a high risk of infection with E. coli O157
or another germ that health officials recommend that people avoid
them completely. These foods include unpasteurized (raw) milk,
unpasteurized apple cider, and soft cheeses made from raw milk.
Sometimes the contact is pretty obvious (working with cows at
a dairy or changing diapers, for example), but sometimes it is
not (like eating an undercooked hamburger or a contaminated piece
of lettuce). People have gotten infected by swallowing lake water
while swimming, touching the environment in petting zoos and other
animal exhibits, and by eating food prepared by people who did
not wash their hands well after using the toilet. Almost everyone
has some risk of infection.
Where
did my infection come from?
Because there are so
many possible sources, for most people we can only guess. If your
infection happens to be part of the about 20% of cases that are
part of a recognized outbreak, the health department might identify
the source.
How
common are STEC infections?
Experts think that
there may be about 70,000 infections with E. coli O157
each year in the United States. We can only estimate because we
know that many infected people do not seek medical care,many do
not submit a stool specimen for testing, and many labs do not
test for STEC. We think that a similar number of persons have
diarrhea caused by non-O157 STEC. Many labs do not identify non-O157
STEC infection because it takes even more work than identifying
E. coli O157.
How
are STEC infections diagnosed?
STEC infections are
usually diagnosed through lab testing of stool specimens (feces).
Identifying the specific strain of STEC involved is very important
for public health purposes, such as finding outbreaks. Most labs
can determine if an STEC is present and can identify E. coli
O157. To determine the O group of non-O157 STEC, strains must
be sent to a State Public Health laboratory.
How
long can an infected person carry STEC?
STEC typically disappear
from the feces by the time the illiness is resolved, but may be
shed for several weeks, even after symptoms go away. Young children
tend to carry STEC longer than adults. A few people keep shedding
these bacteria for several months. Good hand-washing is always
a smart idea to protect yourself, your family, and other persons.
What
is the best treatment for STEC infection?
Non-specific supportive
therapy, including hydration, is important. Antibiotics should
not be used to treat this infection. There is no evidence that
treatment with antibiotics is helpful, and taking antibiotics
may increase the risk of HUS. Antidiarrheal agents like Imodium®
may also increase that risk.
Should
an infected person be excluded from school or work?
School and work exclusion
policies differ by local jurisdiction. Check with your local or
state health department to learn more about the laws where you
live. In any case, good hand-washing after changing diapers, after
using the toilet, and before preparing food is essential to prevent
the spread of these and many other infections.
How
can STEC infections be prevented?
- WASH YOUR HANDS thoroughly
after using the bathroom or changing diapers and before preparing
or eating food. WASH YOUR HANDS after contact with animals or
their environments (at farms, petting zoos, fairs, even your own
backyard)
- COOK meats thoroughly.
Ground beef and meat that has been needle-tenderized should be
cooked to a temperature of at least 160°F/70˚C. It’s
best to use a thermometer, as color is not a very reliable indicator
of “doneness.”
- AVOID raw milk, unpasteurized
dairy products, and unpasteurized juices (like fresh apple cider).
- AVOID swallowing water
when swimming or playing in lakes, ponds, streams, swimming pools,
and backyard “kiddie” pools.
PREVENT cross contamination
in food preparation areas by thoroughly washing hands, counters,
cutting boards, and utensils after they touch raw meat.
Department
of Health and Human Services
Centers for Disease Control and Prevention
http://www.cdc.gov/
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