E. coli Infections: the Facts

Colorectal (Colon) Cancer Slideshow Digestive Disease Myths Slideshow Diverticulitis (Diverticulosis) Slideshow

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Barbara K. Hecht, PhD

Escherichia coli, or E. coli for short, is a very common bacterium. There are hundreds of different strains of E. coli. Some are harmless while others cause serious illness. Non-pathogenic strains of E. coli -- those that do not cause disease -- are normal inhabitants of the intestinal tract in humans and animals. But certain strains of E. coli can cause severe diarrhea and infect the genital and urinary tracts.

The most notorious type of pathogenic E. coli is known as E. coli 0157:H7. The name refers to the chemical compounds found on the surface of the bacterium. This strain was identified in 1982 following an outbreak of diarrhea resulting from the eating of undercooked beef. Outbreaks of E. coli 0157:H7-induced illness have been common in recent years.

Examples of outbreaks include:

• In September 2006, the U.S. Food and Drug Administration advised consumers not to buy or eat raw spinach from any source, citing a widespread outbreak of E. coli infection that led to over 100 cases of illness, including one death. The infections resulted from contamination of raw spinach by E. coli bacteria. It is not clear if the bacterial contamination occurred in the field or during processing of the spinach.



• In 2007, a number of ground beef products were recalled after contamination with E. coli was found, and outbreaks have continued. A restaurant in Effingham, Illinois, was identified as the source of an E. coli outbreak that resulted in at least six confirmed cases of E. coli 0157:H7 among customers in September 2007, and an outbreak also occurred among students at an Indiana elementary school.



• In June 2009, multiple E. coli 0157:H7 infections occurred in people who had consumed raw refrigerated cookie dough.

E. coli 0157:H7 produces toxins that damage the lining of the intestines. The result is severe, bloody diarrhea. Vomiting, abdominal cramps, and fever may also be present.

The main source of E. coli 0157:H7 is healthy cattle, but other domestic and wild mammals also can be sources. During the slaughter of cattle harboring this strain, meat can become contaminated, and the bacteria are mixed into the beef when it is ground. Most cases of E. coli 0157:H7 illnesses have occurred after eating undercooked ground beef. However, other products such as vegetables can become contaminated with the bacteria, for example, if cow manure is used as a fertilizer for produce that is often consumed raw, such as spinach. Sewage contamination of water used for irrigation can also result in contaminated produce. Disease-causing strains of E. coli have been previously identified on lettuce, on alfalfa sprouts, and in unpasteurized fruit juices. It is important to note that rinsing contaminated produce is not sufficient to eliminate the bacterial contamination, but cooking the produce will destroy the E. coli.

These bacteria may also be present on the cow's udders and contaminate the milk and milk products. That is one of the dangers of drinking unpasteurized milk and other raw dairy products. E. coli from the stool of infected people can be spread to others if hygiene is inadequate, which is particularly likely among young children. Swimming and wading pools and hot tubs can harbor live E. coli if the water is under-chlorinated. So can sewage-contaminated drinking water. (This is a concern after hurricanes and other natural disasters.)