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Causes
By Mayo Clinic staffAmong the many strains of E. coli, only a few trigger diarrhea. One group of E. coli — which includes O157:H7 — produces a powerful toxin that damages the lining of the small intestine, which can cause bloody diarrhea.
You develop an E. coli infection when you accidentally ingest the bacteria. Potential sources of exposure include contaminated food or water, and person-to-person contact.
Contaminated food
- Ground beef. When cattle are slaughtered and processed, E. coli bacteria in their intestines can get on the meat. Ground beef combines meat from many different animals, increasing the risk of contamination. Contaminated ground beef often has bacteria spread throughout the mixture — not just on the surfaces (such as on a steak), where cooking is more likely to destroy bacteria.
- Unpasteurized milk. E. coli bacteria on a cow's udder or on milking equipment can get into raw milk.
- Fresh produce. Runoff from cattle farms can contaminate fields where fresh produce is grown. Vegetables such as spinach and lettuce are particularly vulnerable to this type of contamination.
Contaminated water
Human and animal feces may pollute ground and surface water, including streams, rivers, lakes and water used to irrigate crops. Drinking or inadvertently swallowing untreated water from lakes and streams can cause E. coli infection.
Although public water systems use chlorine, ultraviolet light or ozone to kill E. coli, some outbreaks have been linked to contaminated municipal water supplies. Private wells are a greater cause for concern. Some people have been infected after swimming in pools or lakes contaminated with feces.
Personal contact
E. coli bacteria can easily travel from person to person, especially when infected adults and children don't wash their hands properly. Family members of young children with E. coli infection are especially likely to acquire it themselves.
Restaurant workers who don't wash their hands after using the bathroom can transmit E. coli bacteria to food. Outbreaks have also occurred among children visiting petting zoos and in animal barns at county fairs.
- Escherichia coli. Centers for Disease Control and Prevention. http://www.cdc.gov/nczved/dfbmd/disease_listing/stec_gi.html. Accessed May 5, 2009.
- Steckelberg JM (expert opinion). Mayo Clinic, Rochester, Minn. May 12, 2009.
- Bitteman RA, et al. Acute gastroenteritis. In: Marx JA, et al. Rosen's Emergency Medicine: Concepts and Clinical Practice. 6th ed. Philadelphia, Pa.: Mosby Elsevier; 2006. http://www.mdconsult.com/das/book/body/135505615-6/837468548/1365/282.html#4-u1.0-B0-323-02845-4..50098-6--cesec40_4619. Accessed May 5, 2009.
- Calderwood SB. Microbiology, pathogenesis and epidemiology of enterohemorrhagic Escherichia coli. http://www.uptodate.com/home/index.html. Accessed May 5, 2009.
- Basic information about E. coli O157:H7 in drinking water. U.S. Environmental Protection Agency. http://www.epa.gov/safewater/contaminants/ecoli.html. Accessed May 5, 2009.
- Hemolytic uremic syndrome in children. National Institute of Diabetes and Digestive and Kidney Diseases. http://kidney.niddk.nih.gov/kudiseases/pubs/childkidneydiseases/hemolytic_uremic_syndrome/. Accessed May 5, 2009.
- Calderwood SB. Clinical manifestations, diagnosis, treatment and prevention of enterohemorrhagic Escherichia coli. http://www.uptodate.com/home/index.html. Accessed May 5, 2009.
