E. coli (aka Escherichia coli) are a large and diverse group of Gram-negative, bacilli bacteria that normally live in the intestines of people and animals. Most E. coli are harmless and actually are an important part of a healthy human intestinal tract.
However, some E. coli are pathogenic, meaning they can cause illness, either diarrhea or illness outside of the intestinal tract. Shiga toxin is a poison made by some kinds of E. coli bacteria that cause disease. The bacteria that make these toxins are referred to as “Shiga toxin-producing” E. coli or STEC (pronounced ess-tec) for short. Around 5–10% of those who are diagnosed with STEC infection develop a potentially life-threatening complication known as hemolytic uremic syndrome (HUS).
The most commonly identified STEC in North America is E. coli O157:H7 – often shortened to E. coli O157 or even just O157.
The organism can live in the intestines of healthy cattle. Meat can become contaminated during slaughter, and organisms can be thoroughly mixed into beef when it is ground. Bacteria present on the cow’s udders or on equipment may get into raw milk.
Eating meat, especially ground beef that has not been cooked sufficiently to kill E. coli O157:H7 can cause infection.
Contaminated meat looks and smells normal.
Although the number of organisms required to cause disease is not known, it is suspected to be very small. Among other known sources of infection is consumption of sprouts, lettuce, salami, unpasteurized milk (and milk products) and unpasteurized juice, and swimming in or drinking sewage-contaminated water.
Bacteria in diarrheal stools of infected persons can be passed from one person to another if hygiene or hand washing habits are inadequate. This is particularly likely among toddlers who are not toilet trained. Family members and playmates of these children are at high risk of becoming infected.
The time between ingesting the STEC bacteria and feeling sick is called the “incubation period.” The incubation period is usually 3-4 days after the exposure, but may be as short as 1 day or as long as 10 days. The symptoms often begin slowly with mild belly pain or non-bloody diarrhea that worsens over several days. HUS, if it occurs, develops an average 7 days after the first symptoms, when the diarrhea is improving.
Symptoms include bloody diarrhea, dehydration, and abdominal cramps 2-8 days (3-4 on average) after exposure to the organism. In the most severe cases, E.coli poisoning can cause kidney failure.
The very young, older adults and persons with compromised immune systems are the most susceptible to foodborne illness.
Symptoms of HUS may include fever, abdominal pain, pale skin tone, fatigue and irritability, small, unexplained bruises or bleeding from the nose and mouth, decreased urination, and swelling.
Many clinical laboratories do not test for non-O157 Shiga toxin-producing E. coli. STEC such as O26, O103, O45, O111, O121 or O145 are typically harder for clinical laboratories to identify.
Some victims, particularly the very young, can develop a very serious complication, Hemolytic Uremic Syndrome (HUS) which can lead to kidney failure and death. HUS, if it occurs, develops an average seven days after the first symptoms when the diarrhea is improving.
HUS can lead to lifelong complications. In an older population, Thrombotic Thrombocytopenic Purpura (TTP) may be seen. Neurologic symptoms may also be experienced, as well as pancreatitis, diabetes, and high blood pressure.
Non-specific supportive therapy, including hydration, is important.
There is no evidence that treatment with antibiotics is helpful, and taking antibiotics may increase the risk of HUS. Antidiarrheal agents like Imodium® may also increase that risk.
Treatment often just consists of supportive care, with close monitoring of kidney (renal) functioning, hemoglobin, and platelet counts.
Infections start when you swallow STEC—in other words, when you get tiny (usually invisible) amounts of human or animal feces in your mouth. Unfortunately, this happens more often than we would like to think about.
Exposures that result in illness include consumption of contaminated food, consumption of unpasteurized (raw) milk, consumption of water that has not been disinfected, contact with cattle, or contact with the feces of infected people.
Some foods are considered to carry such a high risk of infection with E. coli O157 or another germ that health officials recommend that people avoid them completely.
These foods include unpasteurized (raw) milk, soft cheeses made from raw milk, and unpasteurized apple cider.
Sometimes the contact is pretty obvious (working with cows at a dairy or changing diapers, for example), but sometimes it is not (like eating an undercooked hamburger or a contaminated piece of lettuce).
People have gotten infected by swallowing lake water while swimming, touching the environment in petting zoos and other animal exhibits, and by eating food prepared by people who did not wash their hands well after using the toilet. Almost everyone has some risk of infection.
People of any age can become infected.
Very young children and the elderly are more likely to develop severe illness and hemolytic uremic syndrome (HUS) than others, but even healthy older children and young adults can become seriously ill.
An estimated 265,000 STEC infections occur each year in the United States.
STEC O157 causes about 36% of these infections, and non-O157 STEC cause the rest.
Public health experts rely on estimates rather than actual numbers of infections because not all STEC infections are diagnosed, for several reasons.
However, this situation is changing as more labs have begun using newer, simpler tests that can help detect non-O157 STEC.
Different types of E. coli tend to contaminate different types of foods and water. Previous US outbreaks of pathogenic E. coli have included leafy greens, sprouts, raw milk and cheeses, and raw beef and poultry.
Shiga toxin-producing E. coli (STEC), including E. coli O157:H7, can be particularly dangerous. The primary sources of STEC outbreaks are raw or undercooked ground meat products, raw milk and raw milk cheeses, and contaminated vegetables and sprouts.
STEC infections are usually diagnosed through laboratory testing of stool specimens (feces).
Identifying the specific strain of STEC is essential for public health purposes, such as finding outbreaks. Many labs can determine if STEC are present, and most can identify E. coli O157. Labs that test for the presence of Shiga toxins in stool can detect non-O157 STEC infections.
Contact your healthcare provider if you have diarrhea that lasts for more than 3 days, or it is accompanied by high fever, blood in the stool, or so much vomiting that you cannot keep liquids down and you pass very little urine.
Treatment often just consists of supportive care, with close monitoring of kidney (renal) functioning, hemoglobin, and platelet counts.
There is no evidence that treatment with antibiotics is helpful, and taking antibiotics may increase the risk of HUS. Anti-diarrheal agents may also increase the risk of HUS.
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