E. coli is the name of a common family of bacteria, most members of which do not cause human disease. E. coli O157:H7 is a specific member of this family that can cause bloody diarrhea (hemorrhagic colitis) in man. In the eighteen years since E. coli O157:H7 was first identified as a cause of diarrhea, this bacterium has established a reputation as a significant public health hazard.
Overview of Medical Impacts of E. coli O157:H7
After a susceptible individual ingests a sufficient quantity of E. coli O157:H7, the bacteria attach to the inside surface of the large intestine and initiate an inflammatory reaction. This reaction is believed to be due to chemicals secreted by the bacteria, and results in the bloody diarrhea and abdominal cramps characteristic of the intestinal illness. The incubation period is usually about 3 to 8 days, but slightly more or less is common. A wide spectrum of disease is possible from mild diarrhea without blood, to life-threatening and severe bloody diarrhea with excruciating abdominal pain. In most infected individuals the intestinal illness lasts about a week and resolves without any long-term sequelae. Antibiotics do not improve the illness and some believe these medications might even increase the risk of complications. Apart from good supportive care, which should include close attention to hydration and nutrition, there is no specific therapy. About 5 to 10% of individuals go on to develop hemolytic uremic syndrome (HUS), a severe life-threatening complication of the intestinal illness.
HUS was first described in 1955 and is recognized as the most common cause of kidney failure in childhood. E. coli O157:H7 is responsible for over 90% of the cases of HUS that develop in North America. When HUS follows a diarrhea illness the correct terminology is diarrhea-associated HUS (D+HUS) to distinguish the disease from a less common variety of HUS that occurs as a familial, recurrent, or isolated form associated with other clinical situations.
D+HUS is believed to develop when the E. coli O157:H7 enters into the circulation through the inflamed bowel wall and releases a specific chemical known as shiga-like toxin (SLT). SLT, and most likely other chemical mediators, attach to receptors on the inside surface of blood vessel cells (endothelial cells) and initiate an inflammatory reaction that damages the organs supplied by these tiny arteries. Some organs seem more susceptible, perhaps due to the presence of increased numbers of receptors (kidney, pancreas, and brain). Red blood cells and platelets are also damaged, either directly by the SLT or secondarily due to the clotting process in damaged blood vessels. By definition, when fully expressed, D+ HUS presents with the triad of hemolytic anemia (red blood cells break down), thrombocytopenia (low platelet count), and acute renal failure (loss of the filter function of the kidney).
There is no known therapy to halt the progression of D+HUS. The active stage of the disease usually lasts one to two weeks during which a variety of complications are possible. D+HUS is a frightening illness that even in the best American centers has a mortality rate of about 5%. By comparison, the mortality rate in the developing world is over 75%. About 50% of patients require dialysis due to kidney failure, 25% develop pancreatitis, 25% experience seizures, and 5% suffer from diabetes mellitus. The majority requires transfusion of blood products and develops complications common to the critically ill. The illness is a living nightmare for the patients and families, and leaves a painful memory that lingers long after the acute illness.
Among survivors, about 5% will eventually develop end stage kidney disease with the resultant need for dialysis or transplantation, and another 5 to 10% will develop neurological or pancreatic problems which significantly impair quality of life. Since the longest available follow-up studies of D+HUS are about 20 years, an accurate lifetime prognosis is not available, and as such, lifetime medical follow-up is indicated for even the mildest affected
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