Escherichia coli (E. coli) is a type of bacteria that normally lives in the intestines of humans and animals. Most strains of E. coli are harmless, but some can cause illness. The main causes of E. coli infections are:
- Contaminated food: E. coli can contaminate food during processing, handling, or storage.
- Raw or under-cooked meat. Eating under-cooked or raw meat, especially ground beef, is a common cause of E. coli infections. When cattle are slaughtered and processed, E. coli bacteria in their intestines can get on the meat.
- 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.
- Contaminated water: E. coli can contaminate water sources, such as lakes and streams, and can survive in water for several months. Drinking untreated or contaminated water can cause E. coli infections.
- Person-to-person contact: E. coli can be spread from person to person through contact with fecal matter, especially in settings such as daycare centers and nursing homes.
- Contact with animals: E. coli can be transmitted from animals, especially cattle, to humans through contact with their feces or by consuming contaminated meat or dairy products. Outbreaks have also occurred among children visiting petting zoos and in animal barns at county fairs.
Risk factors
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 from 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 stomach acid, such as esomeprazole (Nexium), pantoprazole (Protonix), lansoprazole (Prevacid) and omeprazole (Prilosec), you may increase your risk of an E. coli infection.
Complications
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.
It’s important to note that not all strains of E. coli cause illness, and even the ones that do can vary in their severity. In general, taking precautions such as cooking meat thoroughly, washing fruits and vegetables, and practicing good hygiene can help reduce the risk of E. coli infections.