Escherichia coli (E. coli) infections
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
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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 Shiga toxin-producing” E.
coli 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 Shiga toxin-producing” E. coli
cause disease. These other kinds are sometimes called “non-O157 Shiga toxin-producing” E.
coli.” 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 Shiga toxin-producing”
E. coli?
Most of what we know about Shiga toxin-producing” E. coli comes from outbreak investigations
and studies of E. coli O157 infection, which was first identified as a pathogen in 1982. The non-
O157 Shiga toxin-producing” E. coli 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 Shiga toxin-producing” E. coli
serogroups can cause the most severe manifestations of Shiga toxin-producing” E. coli illness.

Who gets Shiga toxin-producing” E. coli 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 Shiga toxin-producing” E. coli infections?
The symptoms of Shiga toxin-producing” E. coli 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 Shiga toxin-producing” E. coli infections?
Around 5–10% of those who are diagnosed with Shiga toxin-producing” E. coli 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 Shiga toxin-producing” E. coli 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 Shiga toxin-producing” E. coli come from?
Shiga toxin-producing” E. coli live in the guts of ruminant animals, including cattle, goats, sheep,
deer, and elk. The major source for human illnesses is cattle. Shiga toxin-producing” E. coli that
cause human illness generally do not make animals sick. Other kinds of animals, including pigs
and birds, sometimes pick up Shiga toxin-producing” E. coli from the environment and may
spread it.

How are these infections spread?
Infections start when you swallow Shiga toxin-producing” E. coli—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

How are Shiga toxin-producing” E. coli infections diagnosed?
Shiga toxin-producing” E. coli infections are usually diagnosed through lab testing of stool
specimens (feces). Identifying the specific strain of Shiga toxin-producing” E. coli involved is very
important for public health purposes, such as finding outbreaks. Most labs can determine if an
SShiga toxin-producing” E. coli is present and can identify E. coli O157. To determine the O
group of non-O157 Shiga toxin-producing” E. coli, strains must be sent to a State Public Health

How long can an infected person carry Shiga toxin-producing” E. coli (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 Shiga toxin-producing” E. coli (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.

How can STEC infections be prevented?
1. 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
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.

Reference A1 E. Coli Path Shows Flaws in Beef Inspection New York Times, October 3, 2009
Meat companies and grocers have been barred from selling ground beef tainted by the virulent strain of E. coli known as O157:H7 since
1994. However, many people are still sickened annually by this pathogen. Michael Moss from New York Times explains ground beef is
usually not simply a chunk of meat run through a grinder. Instead, the hamburger meat is a mix of various grades of meat from different
parts of cows and from different slaughterhouses. In a case, a patient ate frozen hamburgers made by Cargill - labelled "American Chef's
Selection Angus Beef Patties" and now she is paralyzed due to a severe strain of E-coli bacteria in a hamburger she ate at her mother's
house in 2007. The ingredients came from four different slaughterhouses. Those low-grade ingredients are cut from areas of the cow that
are more likely to have had contact with feces, which carries E. coli. [A1]