E. coli O157:H7

Frequently Asked Questions

E. coli bacteria, SEM

You hear about E. coli outbreaks in the news all the time, and maybe you’ve even gotten an E. coli infection sometime in the past. But what is E. coli? And why is it a problem?

What Is E. coli?

E. coli is short for Escherichia coli, which is a large, diverse group of bacteria. Most strains of E. coli are harmless and can be found as part of the normal gut flora in the large intestines of mammals, such as cows and sheep.

Since the 1950s, it has been used by scientists as a model for understanding the basic biology of bacteria, as well as a tool for laboratory studies.

Are All Strains of E. coli Bad for You?

Most strains of E. coli are harmless, but certain strains have acquired features that allow them to cause a variety of diseases, including diarrhea, urinary tract infections, respiratory diseases, meningitis and more.

What Is E. coli O157:H7?

E. coli O157:H7 is a strain of the enterohemorrhagic E. coli, also known as EHEC. It is the most common strain described in news reports of foodborne outbreaks of E. coli infections. The strain's name is based on two features of the bacteria: "O" refers to a molecule in the fatty surface of the organism, and "H" refers to the flagella ("haunch" in German means "flagella"), which is the tail-like part that helps the bacteria swim. The various strains of E. coli are classified based on these two molecules.

Since E. coli O157:H7 can grow in the intestines of cows, contamination in the meat-packing and milk industries can lead to foodborne diseases. Produce that has been fertilized with contaminated cow manure can also be a source of disease.

What Are the Symptoms of E. coli O157:H7 Infections?

Symptoms may vary, but include diarrhea (usually bloody), vomiting, and severe stomach cramps.

Fevers are usually absent or very mild. For most people, the infection resolves by around 8 days.

I Think I Have an E. coli infection. What Should I do?

Most cases of E. coli resolve by themselves without the need for medical treatment. However, contact your healthcare provider if you have any concerns about the severity of your disease.

Can I Take Antibiotics or Over-the-Counter Anti-Diarrheal Drug for an E. coli Infection?

No. Both antibiotics and anti-diarrheal drugs have been found to increase the risk for a condition called hemolytic uremic syndrome (HUS), a disease characterized by kidney failure and loss of red blood cells. Always contact your health care provider if you have questions about using over-the-counter drugs.

Where Do You Get E. coli Infections?

Food associated with E. coli have included raw or undercooked meats (e.g., ground beef), deli meats, unpasteurized fruit juices and dairy products, and produce. Other sources of infection have included petting zoos, lake water, and contaminated hands.

How Do You Prevent E. coli Infections?

Use good hygiene, frequent hand washing, and kitchen safety practices.


Escherichia coli. CDC Division of Foodborne, Bacterial and Mycotic Diseases.

Escherichia coli O157:H7. US FDA Bad Bug Book. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook.