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Escherichia coli Infections

(E. coli Infections)

By Larry M. Bush, MD, Affiliate Professor of Clinical Biomedical Sciences;Affiliate Associate Professor of Medicine, Charles E. Schmidt College of Medicine, Florida Atlantic University;University of Miami-Miller School of Medicine

Escherichia coli (E. coli) is a group of gram-negative bacteria that normally reside in the intestine of healthy people, but some strains can cause infection.

  • People develop intestinal E. coli infections by eating contaminated food, touching infected animals, or swallowing contaminated water in a pool.

  • Intestinal infections can cause diarrhea, sometimes severe or bloody, and abdominal pain.

  • Antibiotics can effectively treat E. coli infections outside the digestive tract and most intestinal infections but are not used to treat intestinal infections by one strain of these bacteria.

Some strains of E. coli normally inhabit the digestive tract of healthy people. However, some strains of E. coli have acquired genes that enable them to cause infection in the digestive tract and in other parts of the body, most commonly the urinary tract. E. coli is the most common cause of bladder infection in women.

These bacteria can also cause infection of the prostate gland (prostatitis), gallbladder infection, infections that develop after appendicitis and diverticulitis, wound infections (including wounds made during surgery), infections in pressure sores, foot infections in people with diabetes, pneumonia, meningitis in newborns, and bloodstream infections. Many E. coli infections affecting areas outside the digestive tract develop in people who are debilitated, who are staying in a health care facility, or who have taken antibiotics.

These bacteria can also cause infections outside the intestine if the intestine is torn or damaged—for example, by an injury or a disorder, such as inflammatory bowel disease. Then, the bacteria may leave the intestine and spread to nearby structures that have no defenses against them or they may enter the bloodstream.

One strain produces a toxin that causes brief watery diarrhea. This disorder (called traveler’s diarrhea) usually occurs in travelers who consume contaminated food or water in areas where water is not adequately purified.

E. coli O157:H7 infection

Certain strains of E. coli produce a toxin that damages the colon and causes severe inflammation (colitis). In North America, E. coli O157:H7 is the most common of these strains, but there are over 100 others. These strains are sometimes collectively referred to as enterohemorrhagic E. coli (entero means intestinal, and hemorrhagic means bleeding).

People are usually infected with these strains by doing the following:

  • Eating contaminated ground beef that is not cooked thoroughly (one of the most common sources)

  • Going to a petting zoo and touching animals that carry the bacteria in their digestive tract

  • Eating ready-to-eat food (such as produce at salad bars) that was washed with contaminated water or contaminated by cattle manure

  • Swallowing inadequately chlorinated water that has been contaminated by the stool of infected people in swimming or wading pools

Inadequate hygiene, particularly common among young children in diapers, can easily spread the bacteria from person to person.


E. coli symptoms depend on the part of the body affected and the strain of E. coli causing the infection.

Did You Know...

  • E. coli is the most common cause of bladder infection in women.

Traveler's diarrhea

People with traveler’s diarrhea have abdominal cramping and watery diarrhea and sometimes nausea and vomiting. Symptoms are usually mild and resolve in 3 to 5 days.

E. coli O157:H7

In infections due to E. coli O157:H7 and other enterohemorrhagic E. coli, symptoms begin about 3 days after exposure. People have severe abdominal cramps and watery diarrhea, which may become bloody within 24 hours. (This disease is sometimes called hemorrhagic colitis.) People usually have severe abdominal pain and diarrhea many times a day. They also often feel an urge to defecate but may not be able to. Most people do not have a fever.

Because the infection is easily spread, people must often be hospitalized and isolated.

The diarrhea resolves on its own in 85% of people, usually in 1 to 8 days.

However, hemolytic-uremic syndrome develops in about 5% to10% of people (mainly children under 5 years and adults over 60 years) about 1 week after symptoms begin. In this syndrome, red blood cells are destroyed (called hemolysis), and kidney failure occurs, causing toxic substances to build up in the blood (called uremia). This complication is a common cause of chronic kidney disease in children.

E. coli O157:H7 infection may result in death, especially in older people, whether hemolytic-uremic syndrome develops or not.


  • Culture of samples of infected tissue

Samples of blood, stool, sometimes urine, or other infected material are taken and sent to a laboratory to grow (culture) the bacteria. Identifying the bacteria in the sample confirms the diagnosis.

If the bacteria are identified, they may be tested to see which antibiotics are effective (a process called susceptibility testing).

If E. coli O157:H7 is detected, blood tests must be done frequently to check for hemolytic-uremic syndrome.


  • Various treatments depending on the infection

  • For traveler's diarrhea, loperamide and sometimes antibiotics

  • For diarrhea due to E. coli O157:H7, fluids

  • For many other infections, antibiotics

Treatment varies depending on

  • Where the infection is

  • How severe it is

  • Which type of E. coli is causing it

For example, if infections have caused an abscess, surgery may be done to drain the pus.

Traveler's diarrhea

People with traveler’s diarrhea should drink plenty of fluids.

Loperamide can be given to slow movement of food through the intestine and thus help control diarrhea. This drug is not used if people have a fever, have bloody stools, or are under 2 years old.

If diarrhea is moderate to severe, antibiotics (such as azithromycin, ciprofloxacin, or rifaximin) are usually given to end symptoms more quickly. Antibiotics are usually not needed for mild diarrhea.

If diarrhea is accompanied by a fever or is bloody, travelers should see a doctor.

Diarrhea due to E. coli O157:H7

Many people with diarrhea due to E. coli O157:H7 need to be given fluids containing salts intravenously.

This infection is not treated with loperamide or antibiotics. Antibiotics may make diarrhea worse and increase the risk of hemolytic-uremic syndrome.

If hemolytic-uremic syndrome develops, people are admitted to an intensive care unit and may require hemodialysis.

Other E. coli infections

Many other E. coli infections, usually bladder or other urinary tract infections, are treated with antibiotics, such as trimethoprim/sulfamethoxazole or a fluoroquinolone. However, many bacteria, particularly those acquired in a health care facility, are resistant to some antibiotics. To increase the chances that antibiotics will be effective, doctors may use several antibiotics together until they get the test results indicating which antibiotics are likely to be effective. After they get the results, they change the antibiotic used if needed.

For more serious infections, antibiotics that are effective against many different bacteria (broad-spectrum antibiotics) may be used.

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