Shiga toxin-producing E. coli facts
- Escherichia coli, or E. coli for short, is a very common bacterium.
- There are hundreds of different strains of E. coli. Some are harmless while others cause serious illness.
- Non-pathogenic strains of E. coli -- those that do not cause disease -- are normal inhabitants of the intestinal tract in humans and animals.
- But certain strains of E. coli can cause severe diarrhea and infect the genital and urinary tracts.
Examples of Shiga toxin-producing E. coli outbreaks
The most notorious type of pathogenic E. coli is known as E. coli 0157:H7. The name refers to the chemical compounds found on the surface of the bacterium. This strain was identified in 1982 following an outbreak of diarrhea resulting from the eating of undercooked beef. The 0157:H7 E coli strain belongs to a group of bacteria known as "Shiga toxin-producing" E. coli, or STEC for short. They have also been referred to as verocytotoxic E. coli (VTEC) or enterohemorrhagic E. coli (EHEC). Outbreaks of E. coli 0157:H7-induced illness have been common in recent years. In 2011, a deadly outbreak began in Europe due to a rare strain of E coli, Shiga toxin-producing E. coli O104, or STEC O104, that produces a serious illness similar to that produced by E coli 0157:H7. At the time of the outbreak, which was centered in Germany and related to contaminated vegetables, the STEC 0104 strain had never been identified in the United States.
Examples of other outbreaks include:
- In September 2006, the U.S. Food and Drug Administration advised consumers not to buy or eat raw spinach from any source, citing a widespread outbreak of E. coli infection that led to over 100 cases of illness, including one death. The infections resulted from contamination of raw spinach by E. coli bacteria. It is not clear if the bacterial contamination occurred in the field or during processing of the spinach.
- In 2007, a number of ground beef products were recalled after contamination with E. coli was found, and outbreaks have continued. A restaurant in Effingham, Illinois, was identified as the source of an E. coli outbreak that resulted in at least six confirmed cases of E. coli 0157:H7 among customers in September 2007, and an outbreak also occurred among students at an Indiana elementary school.
- In June 2009, multiple E. coli 0157:H7 infections occurred in people who had consumed raw refrigerated cookie dough.
- In April and May 2012, 14 individuals became infected in an outbreak with the Shiga-toxin producing bacterial strain known as STE 0415 in six US states.
Shiga toxin-producing E. coli infection symptoms
Shiga toxin-producing E. coli infection transmission
- The main source of E. coli 0157:H7 is healthy cattle, but other domestic and wild mammals also can be sources. During the slaughter of cattle harboring this strain, meat can become contaminated, and the bacteria are mixed into the beef when it is ground. Most cases of E. coli 0157:H7 illnesses have occurred after eating undercooked ground beef.
- However, other products such as vegetables can become contaminated with the bacteria, for example, if cow manure is used as a fertilizer for produce that is often consumed raw, such as spinach.
- Sewage contamination of water used for irrigation can also result in contaminated produce. Disease-causing strains of E. coli have been previously identified on lettuce, on alfalfa sprouts, and in unpasteurized fruit juices. It is important to note that rinsing contaminated produce is not sufficient to eliminate the bacterial contamination, but cooking the produce will destroy the E. coli bacterium.
- These bacteria may also be present on the cow's udders and contaminate the milk and milk products. That is one of the dangers of drinking unpasteurized milk and other raw dairy products.
- E. coli from the stool of infected people can be spread to others if hygiene is inadequate, which is particularly likely among young children. Swimming and wading pools and hot tubs can harbor live E. coli if the water is under-chlorinated.
- E. coli can be spread from sewage-contaminated drinking water. (This is a concern after hurricanes and other natural disasters.)
Shiga toxin-producing E. coli 0157:H7 infection complications
The most serious complication of infection with E. coli 0157:H7 is the hemolytic syndrome (HUS). Children under 5 years of age and the elderly are particularly susceptible to this potentially fatal condition characterized by the destruction of red blood cells and kidney failure. Hemolytic syndrome occurs in 5%-10% of people diagnosed with E. coli 0157:H7 infection. HUS is the most common cause of kidney failure in children in the U.S. and must be treated in a hospital setting. The 2011 European outbreak of E. coli STEC 0104 is also associated with this potentially fatal and serious complication.
The CDC estimates that the 0157:H7 strain is responsible for an average of 70,000 cases of infection a year in the U.S., and in total, an estimated 265,000 STEC infections occur each year in the United States. Other disease-causing strains of E. coli that have been found in the U.S. are 026:H11 and 0111:H8.
Shiga toxin-producing E. coli diagnosis
The diagnosis of E. coli infection is done by testing the stool for the presence of the bacteria.
Shiga toxin-producing E. coli infection treatment
Most infected people recover without specific treatment in five to seven days. Antibiotics have not been shown to improve the course of the disease, and experts advise against taking antidiarrheal medications such as loperamide (Imodium).
Shiga toxin-producing E. coli prevention
People can help prevent the spread of E. coli infection and reduce contamination of foods by:
- thoroughly cooking ground beef,
- avoiding unpasteurized milk and juices, and
- practicing proper hygiene, including adequate hand washing.
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REFERENCE: CDC.gov. Escherichia coli O157:H7 and other Shiga toxin-producing Escherichia coli (STEC).
Previous contributing editor: Barbara K. Hecht, PhD