Escherichia coli (abbreviated as E. coli) are a large and diverse group of bacteria. Although most strains of E. coli are harmless, others can make you sick. Some kinds of E. coli can cause diarrhea, while others cause urinary tract infections, respiratory illness and pneumonia, and other illnesses. Still other kinds of E. coli are used as markers for water contamination—so you might hear about E. coli being found in drinking water, which are not themselves harmful, but indicate the water is contaminated.
Some kinds of E. coli cause disease by making a toxin called Shiga toxin. The bacteria that make these toxins are called "Shiga toxin-producing" E. coli, or STEC for short. You might hear these bacteria called verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC); these all refer generally to the same group of bacteria. The strain of Shiga toxin-producing E. coli O104:H4 that caused a large outbreak in Europe in 2011 was frequently referred to as EHEC. The most commonly identified STEC in North America is E. coli O157:H7 (often shortened to E. coli O157 or even just "O157"). When you hear news reports about outbreaks of "E. coli" infections, they are usually talking about E. coli O157.
Most of what we know about STEC comes from outbreak investigations and studies of E. coli O157 infection, which was first identified as a pathogen in 1982. The non-O157 STEC are not nearly as well understood, partly because outbreaks due to them are rarely identified. As a whole, the non-O157 serogroup is less likely to cause severe illness than E. coli O157; however, some non-O157 STEC serogroups can cause the most severe manifestations of STEC illness.
Symptoms of E. coli O157:H7 include watery or bloody diarrhea, fever, abdominal cramps, nausea, and vomiting. Illness may be mild or severe. Usually little or no fever is present, and the illness resolves in 5 to 10 days.
Young children are more likely to have severe symptoms, including kidney failure.
Most people recover without antibiotics or other specific treatment in 5-10 days. There is no evidence that antibiotics improve the course of disease, and it is thought that treatment with some antibiotics may cause kidney complications. Antidiarrheal agents, such as loperamide (Imodium®), is usually avoided. If you think you may be infected see your provider and discuss your options.
Most illness has been associated with eating undercooked, contaminated ground beef. Contaminated meat may look and smell normal.
Person-to-person contact in families and childcare centers is also an important mode of transmission.
Other possible sources of infection are unwashed vegetables, salami, unpasteurized milk and juice, and swimming in or drinking sewage-contaminated water.
Because there are so many possible sources, for most people we can only guess. If your infection happens to be part of the about 20% of cases that are part of a recognized outbreak, the health department might identify the source.
People can help prevent E. coli O157:H7 infection by thoroughly cooking ground beef, washing their hands, avoiding unpasteurized milk, and washing fruits and vegetables.
Because the organism lives in the intestines of healthy cattle, preventive measures on cattle farms and during meat processing are being investigated.