Shiga toxin-producing Escherichia coli is a group of bacteria strains capable of causing significant human disease. The pathogen is transmitted primarily by food and has become an important pathogen in industrialized North America. The subgroup enterohemorrhagic E. coli includes the relatively important serotype O157:H7, and more than 100 other non-O157 strains. Bower reviews epidemiology and clinical issues associated with this pathogen.
Shiga toxin-producing E. coli infections most frequently present as enteric disease, ranging from mild secretory diarrhea to severe hemorrhagic colitis. The most important complication is hemolytic uremic syndrome, which develops in 5 to 10 percent of patients. Mortality from hemolytic uremic syndrome approaches 5 percent, but up to 30 percent of patients who survive have chronic renal disease. E. coli O157:H7 is the most common strain of this infection that causes diarrhea and hemolytic uremic syndrome in the United States, with an estimated 20,000 infections and 250 deaths annually. Non-O157 strains may cause up to 25 percent of hemolytic uremic syndrome induced by this pathogen in the United States, but these strains are more common in South America and parts of Europe.
Infection is transmitted primarily by food and less commonly by direct contact or water (i.e., contaminated swimming water). Bovine products and foods contaminated with bovine waste are frequent causes of outbreaks. Products that have been implicated include ground beef, salami, raw milk, alfalfa sprouts and unpasteurized apple cider and apple juice. Cattle are an important reservoir, although contaminated pork, poultry and lamb also have been encountered.
Shiga toxin is a family of toxins produced by a variety of organisms, including Shigella dysenteriae type I and Shiga toxin-producing E. coli. These toxins have a cytotoxic effect on intestinal epithelial cells that probably causes the characteristic bloody diarrhea. Systemic spread of Shiga toxin causes renal endothelial cell toxicity and may be responsible for hemolytic uremic syndrome.
Laboratory identification of E. coli O157:H7 is easily performed using specialized media and latex agglutination testing of stool culture. Identification of non-O157 Shiga toxin-producing E. coli strains requires detection of the Shiga toxin gene by polymerase chain reaction or DNA probe, or by identifying the toxin. Enzyme immunoassay and latex agglutination tests have recently become available, making testing easier.
The value of antimicrobial agents in treating Shiga toxin-producing E. coli infections remains uncertain. Treatment does not affect the duration of bloody diarrhea and may even increase the risk of hemolytic uremic syndrome. The use of antimotility agents should be avoided because they appear to prolong bloody diarrhea and increase the incidence of hemolytic uremic syndrome.
The author concludes that surveillance of meat processing and education about meat preparation are the best approaches to prevention of this infection. Irradiation of meat has recently been approved by the U.S. Food and Drug Administration and the U.S. Department of Agriculture in an attempt to decrease bacterial contamination of consumer meat supplies.