Among 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 ingest this strain of bacteria. Potential sources of exposure include contaminated food or water, and person-to-person contact.

Contaminated food

The most common way to acquire an E. coli infection is by eating contaminated food, such as:

  • 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.
  • 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.
  • Restaurant meals. Cooks or servers who don't wash their hands after using the bathroom can transmit E. coli bacteria to food.

Contaminated water

Human and animal feces may pollute ground and surface water, including streams, rivers, lakes and water used to irrigate crops. 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 also 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. Outbreaks have also occurred among children visiting petting zoos and in animal barns at county fairs.

Jul. 28, 2011

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