They also suppress the growth of harmful bacteria in our intestines. E. coli?short for Escherichia coli?are known as "enteric" bacteria. "Enteric" comes from the Greek word for "intestine."

We provide a good place for them to hang out (our intestines), and they help us live by manufacturing vitamins necessary for our health. Note, however, that these helpful bacteria live only in areas of the body that are exposed to air: the intestines and respiratory tract. In a healthy person, E. coli is never found in the bloodstream or body tissues.

There are hundreds of strains of E. coli, and most of them are harmless. The strain E. coli 0157:H7, often shortened to just E. coli 0157, is entirely different from the strains that typically inhabit our intestines. E. coli 0157 produces a toxin that damages the walls of the intestine causing hemorrhaging, or loss of blood, in the intestines.

It is always found around animals, however, which is why children who have visited petting zoos may become ill if they don't wash their hands after petting the animals and before eating. Annually, 70,000 cases of E. coli 0157 infection and about 60 deaths are reported in the United States, according to the Centers for Disease Control and Prevention.

Cases that involve undercooked hamburger can be blamed on the strain of E. coli found in the intestines of cattle. It can contaminate the beef during slaughter. Hamburger meat is more susceptible to contamination because the bacteria are ground into the meat's interior, where temperatures don't get as high during cooking. Other contaminated foods include unpasteurized milk, salami, lettuce, alfalfa and radish sprouts, game meat, and cheese curds. The bacteria also can be spread from one person to another through families and child-care centers that don't practice good hygiene. Another mode of transmission is by swimming in or drinking water that has been contaminated with fecal material. This can include swimming pools, wading pools, unchlorinated water, and groundwater. It is thought that it takes only a small number of bacteria to cause an infection, maybe as few as 10 organisms.

The bacteria produce a toxin (Shiga toxin or verotoxin) that damages the cells that line the walls of the intestine. The illness is called hemorrhagic colitis and causes a loss of water, salts, and blood. A serious complication of this infection is hemolytic uremic syndrome (HUS), a rare condition affecting mostly children under age 10. In HUS, the toxin enters the bloodstream and destroys red blood cells and platelets and damages blood vessel walls. The damaged cells and other debris from the destruction can block small blood vessels in the kidney or damage the kidney itself. The kidneys stop working. In severe cases, the kidneys suffer permanent damage.

HUS, a complication of the infection, is fatal to about half the elderly adults who develop it, and up to 3 percent of young children.

The diarrhea becomes quite bloody. Other possible symptoms include nausea, vomiting, and low-grade fever.

Supportive therapy is the mainstay of treatment and includes fluids, electrolytes, blood transfusions, and dialysis. There is no evidence that antibiotics can help treat this illness, and they may make it worse, experts say. The disease usually resolves itself after five to 10 days, although children may need a significantly longer hospitalization. There is no treatment for HUS; supportive care, such as replacing lost fluids and salts and sometimes blood transfusions, can help.

When cooking hamburger, make sure the internal temperature has reached 160 F to ensure that all bacteria have been killed. Contaminated meat looks and smells normal; only a small amount of E. coli 0157 bacteria need be present to cause illness. Never place cooked meat on a plate that held raw meat unless the plate has been thoroughly washed. The same goes for utensils. In general, be sure to wash your hands thoroughly after using the toilet and before eating.