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Escherichia coli, Diarrhea-Inducing Toxins, and Hemolytic-Uremic Syndrome

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Escherichia coli, usually known as E. coli, is by weight one of the most common bacteria found in human and animal intestines. Like most intestinal bacteria, we need E. coli in our intestines: bacteria help break down food for digestion, and synthesize some nutrients that we should -- but sometimes don't -- eat in our food. (One example is vitamin K, which the liver needs to produce the clotting factors that help us stop bleeding after a wound.)

However, like any bacteria, E. coli can get out of hand. Also, and more important, there are many strains of E. coli, including some, known as toxigenic, that produce toxins. A subgroup of toxigenic E. coli, known as enterohemorrhagic E. coli (or EHEC) and including the strain E. coli O157:H7, produces toxin similar to that made by Shigella, a well-known bacterial cause of gastroenteritis. In addition, enterohemorrhagic E. coli can attach themselves to the epithelial cells that line the inside wall of the intestines. The toxins produced by enterohemorrhagic E. coli enter the bloodstream and eventually damage blood vessels elsewhere in the body.

Problems caused by EHEC may take from 1-9 days to appear after a person is exposed to the bacteria. The problems include:

Diarrhea
usually bloody diarrhea because of blood vessel damage, although diarrhea without blood does occur in EHEC infections. Almost all patients with E. coli O157:H7 infection develop bloody diarrhea. The diarrhea may be short-lived, or may be more chronic. As many as half of patients with EHEC-associated diarrhea need to be hospitalized, and 1-2% of patients with EHEC diarrhea may die.
Hemolytic-Uremic Syndrome (HUS)
This is a combination of thrombocytopenia (a very low platelet count), hemolytic anemia (anemia due to hemolysis, or destruction of red blood cells), and acute kidney failure. HUS may also affect the brain (strokes, seizures, coma, partial paralysis, and blindness due to damage to the part of the brain that process information from the eyes), the heart (due to reduced blood flow through the heart muscle), the digestive system (bloody diarrhea as above, but also bowel wall damage and perforation, intussusception or liver inflammation), the pancreas (resulting in temporary or permanent diabetes), or the production of white blood cells. HUS is the most common cause of acute kidney failure in children less than 3 years old.

Supportive care is the usual treatment for enterohemorrhagic E. coli infections. Antibiotics do not shorten the time that diarrhea lasts, and may increase the risk of developing HUS. Medicines that may lessen or stop diarrhea in other forms of gastroenteritis can worsen HUS and its complications.

The best treatment for enterohemorrhagic E. coli infection is to prevent it in the first place. Proper handwashing is always important, especially when playing with animals or when handling meat. E. coli O157:H7 is found in as many as 1 out of 10 cattle, both in their intestines and in their stool, although they can carry E. coli without developing disease. Other animals including sheep, deer, and goats can also carry E. coli O157:H7 in their intestines and their stools. It takes very few E. coli O157:H7 bacteria to infect someone who eats contaminated meat (as few as 10 to 100 bacterial cells), so undercooked meat may carry enough live E. coli to get things started, and one small piece of meat may have enough E. coli to contaminate massive amounts -- as we saw in the recent (September-October, 2007) incident in which 22 million pounds of ground beef had to be recalled and the company that processed the ground beef went out of business as a result. One way to reduce or eliminate the risk of infection from contaminated ground beef is to eat burgers only if they are well-done. Vegetables and fruit that come in contact with stool from infected animals or water contaminated by that stool can also transmit the disease: in recent years we have seen outbreaks of E. coli O157:H7 infection traced to spinach, lettuce, and scallions supplied to the restaurants where the patients were eating. Cooking vegetables, and eating freshly-peeled fruits, may help avoid infection if the fruits and vegetables are contaminated. As for playing with animals, there have been several documented outbreaks of E. coli O157:H7 infections that were traced to farm animals in petting zoos -- another good reason to wash your hands after playing with animals.

(Note from Sniff: But we don't have E. coli O157:H7 in our intestines, do we?)
(Editor's note to Cat Scan and Sniff: Not that I know of. That's another reason why your kitty beef is well-done, you know -- and why I don't give you and Cat Scan ground beef.)

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PLEASE NOTE: As with all of this Web site, I try to give general answers to common questions my patients and their parents ask me in my (real) office. If you have specific questions about your child you must ask your child's regular doctor. No doctor can give completely accurate advice about a particular child without knowing and examining that child. I will be happy to try and answer general questions about children's health, but unless your child is a regular patient of mine I cannot give you specific advice. (And Cat Scan and Sniff don't let me try to give advice on cat health.)

Copyright © 2007 Vinay N. Reddy, M.D. All rights reserved.
Written 10/18/07; last revised 10/18/07 counter