Escherichia coli (E. coli) bacteria normally live in the intestines of healthy people and animals. Most varieties of E. coli are harmless or cause relatively brief diarrhea. But a few particularly nasty strains, such as E. coli O157:H7, can cause severe abdominal cramps, bloody diarrhea and vomiting.
You may be exposed to E. coli from contaminated water or food — especially raw vegetables and undercooked ground beef. Healthy adults usually recover from infection with E. coli O157:H7 within a week, but young children and older adults have a greater risk of developing a life-threatening form of kidney failure called hemolytic uremic syndrome.
Signs and symptoms of E. coli O157:H7 infection typically begin three or four days after exposure to the bacteria, though you may become ill as soon as one day after to more than a week later. Signs and symptoms include:
- Diarrhea, which may range from mild and watery to severe and bloody
- Abdominal cramping, pain or tenderness
- Nausea and vomiting, in some people
When to see a doctor
Contact your doctor if your diarrhea is persistent, severe or bloody.
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.
Unlike many other disease-causing bacteria, E. coli can cause an infection even if you ingest only small amounts. Because of this, you can be sickened by E. coli from eating a slightly undercooked hamburger or from swallowing a mouthful of contaminated pool water.
Potential sources of exposure include contaminated food or water and person-to-person contact.
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 cattle, 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. Certain vegetables, such as spinach and lettuce, are particularly vulnerable to this type of contamination.
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 because they don't often have any disinfecting system. Rural water supplies are the most likely to be contaminated. Some people also have been infected after swimming in pools or lakes contaminated with feces.
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.
E. coli can affect anyone who is exposed to the bacteria. But some people are more likely to develop problems than are others. Risk factors include:
- Age. Young children and older adults are at higher risk of experiencing illness caused by E. coli and more-serious complications from the infection.
- Weakened immune systems. People who have weakened immune systems — from AIDS or drugs to treat cancer or prevent the rejection of organ transplants — are more likely to become ill from ingesting E. coli.
- Eating certain types of food. Riskier foods include undercooked hamburger; unpasteurized milk, apple juice or cider; and soft cheeses made from raw milk.
- Time of year. Though it's not clear why, the majority of E. coli infections in the U.S. occur from June through September.
- Decreased stomach acid levels. Stomach acid offers some protection against E. coli. If you take medications to reduce your levels of stomach acid, such as esomeprazole (Nexium), pantoprazole (Protonix), lansoprazole (Prevacid) and omeprazole (Prilosec), you may increase your risk of an E. coli infection.
Most healthy adults recover from E. coli illness within a week. Some people — particularly young children and older adults — may develop a life-threatening form of kidney failure called hemolytic uremic syndrome.
No vaccine or medication can protect you from E. coli-based illness, though researchers are investigating potential vaccines. To reduce your chance of being exposed to E. coli, avoid risky foods and watch out for cross-contamination.
Cook hamburgers until they're 160 F. Hamburgers should be well-done, with no pink showing anywhere in the meat. But color isn't a reliable indicator of whether or not meat is done cooking. Meat — especially if grilled — can brown before it's completely cooked.
That's why it's important to use a meat thermometer to ensure that meat is heated to at least 160 F (71 C) at its thickest point.
- Drink pasteurized milk, juice and cider. Any boxed or bottled juice kept at room temperature is likely to be pasteurized, even if the label doesn't say so.
- Wash raw produce thoroughly. Washing produce won't necessarily get rid of all E. coli — especially in leafy greens, which provide many spots for the bacteria to attach themselves to. Careful rinsing can remove dirt and reduce the amount of bacteria that may be clinging to the produce.
- Wash utensils. Use hot soapy water on knives, countertops and cutting boards before and after they come into contact with fresh produce or raw meat.
- Keep raw foods separate. This includes using separate cutting boards for raw meat and foods, such as vegetables and fruits. Never put cooked hamburgers on the same plate you used for raw patties.
- Wash your hands. Wash your hands after preparing or eating food, using the toilet, or changing diapers. Make sure that children also wash their hands before eating, after using the bathroom and after contact with animals.
Mayo Clinic Minute: Avoiding summer E. coli infection
Cook this incorrectly, and you could end up with a case of E. coli.
"E. coli stands for Escherichia coli, which is a type of bacteria."
"Most commonly, we hear about it in raw or undercooked hamburger meat."
Dr. Nipunie Rajapakse says E. coli bacteria can create some stomach-turning symptoms, like abdominal pain and nausea. But it can get even worse.
"There’s a specific type of E. coli. It's called O157:H7, which can cause bloody diarrhea and has been associated with a condition that can cause kidney damage, especially in young children."
The elderly are also at higher risk for problems with E. coli, as are pregnant women, people with underlying digestive problems and those with weakened immune systems.
"If somebody were to be exposed to E. coli in something they ate or drank, they may have symptom onset within a couple of days to a few weeks after infection or exposure."
Dr. Rajapakse says the best way to avoid a bout with the bacteria is to wash your hands and thoroughly cook your hamburgers.
For the Mayo Clinic News Network, I'm Jeff Olsen.