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Escherichia coli Infections

by Matthew E. Levison, MD

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 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.

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

Another strain ( E. coli O157:H7) produces a toxin that damages the colon and causes inflammation (colitis). People are usually infected with this strain by doing the following:

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

  • Going to a petting 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.


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

In infections due to E. coli O157:H7, diarrhea begins about 3 days after exposure. Diarrhea becomes bloody about 1 to 3 days later. (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. However, in about 15% of children and fewer older people, red blood cells are destroyed and kidney failure occurs about 1 week after symptoms begin. This complication (called hemolytic-uremic syndrome—see Thrombotic thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS)) is a common cause of chronic kidney disease in children.

Did You Know...

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


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.


For traveler’s diarrhea, loperamide can be given to slow movement of food through the intestine and thus help control diarrhea. Antibiotics (such as azithromycin, ciprofloxacin, or rifaximin) can also be given to end symptoms more quickly.

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.

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 these antibiotics. For more serious infections, antibiotics that are effective against many different bacteria (broad-spectrum antibiotics) may be used. Several antibiotics may be used together until doctors get the test results indicating which antibiotics are likely to be effective.

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