What is E. Coli?

Medically Reviewed by Carol DerSarkissian, MD on December 08, 2022
4 min read

E. coli (Escherichia coli), is a type of bacteria that normally lives in your intestines. It’s also found in the gut of some animals.

Most types of E. coli are harmless and even help keep your digestive tract healthy. But some strains can cause diarrhea if you eat contaminated food or drink fouled water.

While many of us associate E. coli with food poisoning, you can also get pneumonia and urinary tract infections from different types of the bacteria. In fact, 75% to 95% of urinary tract infections are caused by E. coli. E.coli is a normal resident of the bowel, which is how it makes it way to the urinary tract.

Some versions of E. coli make you sick by making a toxin called Shiga. This toxin damages the lining of your intestine. The strains of E. coli that make the toxin are sometimes called STEC, which is short for “Shiga toxin-producing E. coli.”

One especially bad strain, O157:H7, can make you very sick. It causes abdominal cramps, vomiting, and bloody diarrhea. It is the leading cause of acute kidney failure in children. It can also cause life-threatening symptoms such as:

You should get emergency help if you have any of these symptoms.

You can become infected when you swallow even a small amount of E. coli bacteria. Among the ways this can happen:

  • Ground meat: You eat ground meat that carries E. coli, and the meat wasn’t cooked enough to kill the bacteria. When meat is processed, sometimes bacteria from the animals’ intestines make their way into the meat. This happens more with ground meat because it comes from more than one animal.
  • Untreated milk: You drink unpasteurized milk, which hasn’t been heated to kill bacteria. E. coli can get into the milk from the cow’s udder or from milking equipment.
  • Vegetables and fruit: You might eat fresh vegetables or fruit that’s been tainted by water that has the bacteria. This happens most often when manure from nearby animals mixes with the water supply.
  • Other foods and beverages: You might also get E. coli from unpasteurized fruit juices and yogurt and cheese made from raw milk.
  • Water: You swallow water that contains E. coli, perhaps while swimming in a pool, lake, or pond.
  • Other people: You might get E. coli from another person who has it, such as a child. The bacteria can be passed to you if you clean up after an infected person and then don’t wash your hands really well before you touch your mouth.
  • Animals: It can be found at petting zoos or animal exhibits at fairs.

You can also contaminate food in your own kitchen if you allow a knife or cutting board that has touched uncooked meat (like chicken) to come into contact with food that will be eaten raw (like a salad).

You’ll probably start to feel ill 2 to 5 days after you’ve taken in the E. coli bacteria. The most common symptoms are:

  • Abdominal cramps
  • Diarrhea, which may be bloody
  • Nausea
  • Constant fatigue

You may not have a fever. If you do, it may be slight.

Healthy people infected with E. coli usually feel better within a week. But some people have a serious complication called hemolytic uremic syndrome, which affects the kidneys. This is more likely to happen to older people and children.

The only way your doctor can know for sure if you have an E. coli infection is to send a sample of your stool to a lab to be analyzed.

Fortunately, the infection usually goes away on its own.

For some types of E.coli associated with diarrhea, such as the watery travelers’ diarrhea, antibiotics can shorten the length of time you have symptoms and might be used in moderately severe cases.

But if you have fever or bloody diarrhea or if your doctor suspects Shiga toxin-producing E. coli, antibiotics should not be taken. They can actually increase the production of Shiga toxin and worsen your symptoms.

It’s important to rest and get plenty of fluids to replace what your body is losing through vomiting or diarrhea.

Don’t take over-the-counter medications that fight diarrhea. You don’t want to slow down your digestive system, because that will delay your body’s shedding of the infection.

When you start to feel better, stick to low-fiber foods at first such as:

  • Crackers
  • Toast
  • Eggs
  • Rice

Dairy products and foods that are high in fat or fiber can make your symptoms worse.

One of the most important things you can do to protect yourself and your family against E. coli is wash your hands, particularly in these situations:

  • Before you prepare food
  • Before preparing bottles or food for infants or toddlers
  • Before touching anything, such as a pacifier, that goes into a small child’s mouth.
  • After you’ve used the bathroom or changed a diaper
  • After you’ve had contact with animals, even your own pets
  • After handling raw meat

You can also prevent E. coli infections by being careful about the foods that carry the greatest chance of contamination:

  • Cook hamburgers until they’re 160 F inside.
  • Drink only pasteurized milk, juice, and cider.
  • Wash all of your produce before you eat it. Be especially careful to get dirt off leafy greens such as lettuce and spinach.

In your kitchen, a couple of simple rules will help keep you safe:

Wash: Clean knives, counters, and cutting boards with hot, soapy water after raw meat has touched them.

Keep raw and cooked separate: Use different cutting boards for food that you eat raw, such as vegetables and fruit. Don’t put cooked meat back on the same plate you used for raw meat without washing the plate first.

When you're swimming, try not to swallow the water, whether it's a pool, a lake, or the ocean. It may be tainted with E. coli from feces.