E. coli 0157:H7 in drinking water -- US EPA
E. coli in drinking water
One of hundreds of strains of the bacterium
Escherichia coli, E. coli
O157:H7 is an emerging cause of foodborne and waterborne illness.
Although most strains of E. coli
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 during an outbreak in 1982
traced to contaminated hamburgers. Since then, most infections are
believed to have come from eating undercooked ground beef.
However, some have been waterborne. In 1999, people became sick
after drinking contaminated water in Washington County, New York and
swimming in contaminated water in Clark County, Washington.
Information about the health effects of
E. coli O157:H7, and actions
you can take to protect yourself and your family from
E. coli infection is provided
below. You can also read
the Centers for Disease Control and Prevention fact sheet on E.
coli and the Food and
Drug Administration Bad Bug Book.
What is E. coli and where does it come from?
E. coli is a type of fecal
coliform bacteria commonly found in the intestines of animals and
humans. E. coli is short for
Escherichia coli. The presence
of E. coli in water is a strong
indication of recent sewage or animal waste contamination. Sewage
may contain many types of disease-causing organisms.
What are fecal coliforms?
Fecal coliforms are bacteria that are associated with human or
animal wastes. They usually live in human or animal intestinal
tracts, and their presence in drinking water is a strong indication
of recent sewage or animal waste contamination.
How does E. coli or other fecal coliforms get in the water?
E. coli comes from human and
animal wastes. During rainfalls, snow melts, or other types of
precipitation, E. coli may be
washed into creeks, rivers, streams, lakes, or groundwater. When
these waters are used as sources of drinking water and the water is
not treated or inadequately treated, E. coli may end up in drinking water.
What are the health effects of E. coli O157:H7?
E. coli O157:H7 is one of
hundreds of strains of the bacterium E. 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. Infection often causes
severe bloody diarrhea and abdominal cramps; sometimes the infection
causes non-bloody diarrhea. Frequently, no fever is present. It
should be noted that these symptoms are common to a variety of
diseases, and may be caused by sources other than contaminated
In some people, 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. 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%.
How long does it take for these symptoms of E. coli O157:H7 infection to occur?
Symptoms usually appear within 2 to 4 days, but can take up to 8
days. Most people 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.
What should I do if I have any of the above symptoms?
Consult with your physician. 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.
Are there groups of people who are at greater risk of getting any of the symptoms?
Children under the age of five, the elderly, and people whose
health is weakened (i.e., people who have long-term illnesses such
as cancer or AIDS) are at greater risk of severe illness.
What should these people who are at greater risk do? Are there any additional precautions they should take?
People who are at greater risk should consult with their doctor
or health care provider and follow the instructions provided.
How will I know if my water is safe?
If you get your water from a public water system, then your water
system is required by law to notify you if your water is not safe.
If you are interested in obtaining information about your drinking
water, consult the water quality report that you should receive
annually from your local water system, or call your local water
system directly. Information on local water systems is also
available on EPA's web site at
How is water treated to protect me from E. coli?
The water can be treated using chlorine, ultra-violet light, or
ozone, all of which act to kill or inactivateE.
coli. Systems using surface water sources are required to
disinfect to ensure that all bacterial contamination is inactivated,
such as E. coli. Systems using
ground water sources are not required to disinfect, although many of
If I have a private well, how can I have it tested for E. coli?
If you have a private well, you should have your water tested
periodically. Contact your State laboratory certification officer
to find out which laboratories have been certified for conducting
total coliform analyses. (You may contact the Safe Drinking Water
Hotline at 1-800-426-4791 for the address and phone number of this
individual.) Then contact a certified lab near you and get
instructions on how to send them a water sample. Typically, the lab
will first test for total coliforms, which is a group of related
organisms that is common in both the environment and in the gut of
animals. If the sample is positive for total coliforms, the lab
will determine whether E. coli is also present.
E. coli is a type of total
coliform that is closely associated with recent fecal
contamination. Few E. coli strains cause disease. However,
the presence of any E. coli in
a water sample suggests that disease-causing organisms, are also
likely to be present.
One of the strains of E. coli
that causes disease is E. coli
O157:H7. EPA does not believe it necessary for an owner of a
private well to test specifically for this organism under normal
circumstances. If E. coli
O157:H7 is present in your well, it is highly likely that other
strains of E. coli are also
present. If a well is E. coli-positive,
regardless of strain, you should not drink the water unless it is
disinfected. Several tests are available for determining whether
E. coli O157:H7 is present, but
they are somewhat more expensive than the standard E. coli
tests and many labs may not have the expertise or supplies to
perform these tests. Your state's laboratory certification officer
should be able to tell you which laboratories can perform these
tests, or you can contact the lab directly.
If my well is contaminated with E. coli, what can I do to protect myself?
If your well tests positive for E.
coli, do not drink the water unless you boil it for at least
one minute at a rolling boil, longer if you live at high altitudes.
You may also disinfect the well according to procedures recommended
by your local health department. Monitor your water periodically
after disinfection to make certain that the problem does not recur.
If the contamination is a recurring problem, you should investigate
the feasibility of drilling a new well or install a point-of-entry
disinfection unit, which can use chlorine, ultraviolet light, or
How does the U.S. Environmental Protection Agency regulate E. coli?
According to EPA regulations, a system that operates at least 60
days per year, and serves 25 people or more or has 15 or more
service connections, is regulated as a public water system under the
Safe Drinking Water Act. If a system is not a public water system
as defined by EPA's regulations, it is not regulated under the Safe
Drinking Water Act, although it may be regulated by state or local
Under the Safe Drinking Water Act, EPA requires public water
systems to monitor for coliform bacteria. Systems analyze first for
total coliform, because this test is faster to produce results. Any
time that a sample is positive for total coliform, the same sample
must be analyzed for either fecal coliform or
E. coli. Both are indicators
of contamination with animal waste or human sewage.
The largest public water systems (serving millions of people)
must take at least 480 samples per month. Smaller systems must take
at least five samples a month unless the state has conducted a
sanitary survey – a survey in which a state inspector examines
system components and ensures they will protect public health – at
the system within the last five years.
Systems serving 25 to 1,000 people typically take one sample per
month. Some states reduce this frequency to quarterly for ground
water systems if a recent sanitary survey shows that the system is
free of sanitary defects. Some types of systems can qualify for
Systems using surface water, rather than ground water, are
required to take extra steps to protect against bacterial
contamination because surface water sources are more vulnerable to
such contamination. At a minimum, all systems using surface waters
must disinfect. Disinfection will kill E. coli O157:H7.
What can I do to protect myself from E. coli O157:H7 in drinking water?
Approximately 89 percent of Americans are receiving water from
community water systems that meet all health-based standards. Your
public water system is required to notify you if, for any reason,
your drinking water is not safe. If you wish to take extra
precautions, you can boil your water for one minute at a rolling
boil, longer at higher altitudes. To find out more information
about your water, see the Consumer Confidence Report from your local
water supplier or contact your local water supplier directly. You
can also obtain information about your local water system on EPA's
web site at
If you draw water from a private well, you can contact your state
health department to obtain information on how to have your well
tested for total coliforms and E. coli
contamination. If your well tests positive for
E. coli, there are several
steps that you should take: (1) begin boiling all water intended for
consumption, (2) disinfect the well according to procedures
recommended by your local health department, and (3) monitor your
water quality to make certain that the problem does not recur. If
the contamination is a recurring problem, you should investigate the
feasibility of drilling a new well or install a point-of-entry
disinfection unit, which can use chlorine, ultraviolet light, or
The Centers for Disease Control and Prevention (CDC) suggests other actions that you may take to prevent
E. coli infection. These include:
- Avoid swallowing lake or pool water while swimming.
- Thoroughly cook ground beef and avoid unpasteurized milk.
- 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 others.
- 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 160º 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 being investigated.
Will a water filter work to keep E. coli out of my water?
Most in-home filters will not. EPA recommends that you boil your
water if you are concerned about its safety.