Definition

Enterohemorrhagic E. coli is one of several intestinal types of E. coli that infect animals and humans. The O157:H7 strain is the member of the group most often associated with a particularly severe form of diarrhea. (The O indicates the somatic antigen, while the H denotes the flagellar antigen, both of which are found on the cell surface of the bacteria.) E. coli O157:H7 is also the most common cause of a unique syndrome, known as the Hemolytic-Uremic Syndrome (HUS), which causes kidney failure. The bacteria was discovered in 1977, and first reports of infections followed in 1982.

Description

The bacteria produces toxins that are very similar to those produced by Shigella, called Shiga toxins. These toxins are lethal for intestinal cells, and also damage the cells that line vessels (endothelial cells). It is believed that the damage to blood vessels results in the formation of clots, which eventually leads to the Hemolytic-Uremic Syndrome. HUS is a serious, often fatal, syndrome that has other causes in addition to E. coli O157:H7; it is characterized by the breaking up of red blood cells (hemolysis) and kidney failure (uremia). The syndrome occurs most often in the very young and very old.

Causes & symptoms

After an incubation period of 3-4 days on average, watery diarrhea begins, which rapidly progresses to bloody diarrhea in many victims, in which case the bowel movement may be mostly blood. Nausea, vomiting, and low-grade fever are also frequently present. Gastrointestinal symptoms last for about one week, and recovery is often spontaneous.

Complications

About 5-10% of individuals, usually at the extremes of age, develop HUS, and ultimately, kidney failure.

Neurological symptoms can also occur as part of HUS and consist of seizures, paralysis, and coma.

Diagnosis

This particular strain of E. coli is suspected when bloody diarrhea is present. Stool cultures are used to tentatively identify the bacteria. Further tests at specialized laboratories are usually needed, however, for confirmation of infection. Unfortunately, cultures are often negative or inconclusive if done after 48 hours of symptoms.

Treatment

Uncomplicated cases of the infection clear up within ten days. It is not certain that antibiotics are helpful in treating E. coli O157:H7 and there is some evidence that they may be harmful. Dehydration resulting from diarrhea must be treated with either Oral Rehydration Solution (ORS) or intravenous fluids. Anti-motility agents, which decrease the intestines ability to contract, should not be used in any patient with bloody diarrhea.

Treatment of HUS, if it develops, involves correction of clotting factors, plasma exchange, and kidney dialysis.

Prognosis

In most cases, symptoms last for about a week and recovery is often spontaneous. Ten percent of individuals with E. coli O157:H7 infection develop HUS; 5% of those will die of the disease. Some who recover from HUS will be left with some degree of kidney damage.

Prevention

Thorough cooking of all meat and poultry products and adhering to proper food preparation is the most effective way to avoid infection. Food irradiation methods are also being developed to sanitize food.

Key Terms

Antigen

A substance, usually a protein, that causes the formation of an antibody and reacts specifically with that antibody.

Anti-motility medications

Medications such as loperamide (Imodium), dephenoxylate (Lomotil), or medications containing Codeine or narcotics which decrease the ability of the intestine to contract. This can worsen the condition of a patient with dysentery or colitis.

Colitis

Inflammation of the colon or large intestine, usually causing diarrhea which may be bloody.

Food irradiation methods

A process using radiant energy to kill microogranisms in food, to extend the amount of time in which food can be sold and eaten safely.

Oral Rehydration Solution (ORS)

A liquid preparation developed by the World Health Organization that can decrease fluid loss in persons with diarrhea. Originally developed to be prepared with materials available in the home, commercial preparations have recently come into use.

Urea

Chemical formed during the body's metabolism of nitrogen and normally excreted by the kidney. Urea levels rise in the blood when kidney failure occurs.

Further Reading

For Your Information

Books

• Hamer, Davidson H., and Sherwood L. Gorbach. "Escherichia coli." In Sleisenger & Fordtran's Gastrointestinal and Liver Disease, edited by Mark Feldman, et al. Philadelphia: W.B. Saunders Company, 1997, pp.1600-1603.
• Thielman, Nathan M., and Richard L. Guerrant. "Food-Borne Illness." In Conn's Current Therapy, 1996, edited by Robert E. Rakel. Philadelphia: W.B. Saunders Company, 1996, pp.89-96.
• Wolfe, Martin S. "Acute Infectious Diarrhea." In Conn's Current Therapy, 1996, edited by Robert E. Rakel. Philadelphia: W.B. Saunders Company, 1996, pp.16-19.

  Periodicals

• Bender, Jeffery B., et. al. "Surveillance for Escherichia coli O157:H7 Infections in Minnesota by Molecular Subtyping." New England Journal of Medicine 337 (6)(1997): 388.
• Rondeau, Eric, and Marie-Noëlle Peraldi. "Escherichia coli and the Hemolytic-Uremic Syndrome." New England Journal of Medicine 335 (9)(1996): 660.
• "Traveler's Diarrhea: Don't Let It Ruin Your Trip." Mayo Clinic Health Letter (January 1997).

  Organizations

• Division of Bacterial and Mycotic Diseases. National Center for Infectious Diseases Centers for Disease Control and Prevention. 1600 Clifton Road, Mailstop C09 Atlanta, Georgia 30333. http://www.cdc.gov.

  Other

• Centers for Disease Control and Prevention, National Center for Infectious Diseases. "Preventing Foodborne Illness: Escherichia coli 0157:H7." (9 August 1996). http://www.cdc.gov/ncidod/diseases/foodborn/e_coli.htm.

Gale Encyclopedia of Medicine. Gale Research, 1999.