Enterohemorrhagic E. coli (EHEC), also known as Shiga-toxin-producing E. coli (STEC), is recognized as an important cause of human diarrhea, hemorrhagic colitis, thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). The E. coli serotype O157:H7 has been documented as the most common cause of sporadic and epidemic outbreaks of EHEC disease. However, it has been discovered recently that more than 100 other non-O157:H7 EHEC serotypes are capable of producing the same disease syndromes, since these serotypes may also produce Shiga toxins.
The traditional laboratory diagnosis of EHEC infection has been dependent on the recovery of E.coli O157:H7 followed by immunologic confirmation; however, culture sensitivity is roughly 50 to 80% and does not detect the presence of non-O157 Shiga-toxin-producing E.coli.
One virulence trait of all EHEC strains is their ability to produce two potent cytotoxins called Shiga toxins. Shiga toxin 1 is identical to the toxin produced by Shigella dysenteriae; Shiga toxin 2 is more commonly associated with HUS than Shiga toxin 1. An EHEC may have either or both toxins present. 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 potentially life-threatening HUS.
EHEC is transmitted primarily by ingestion of contaminated foods such as undercooked meat (especially ground beef), vegetables (spinach, alfalfa sprouts, etc.) and unpasteurized fruit juices or dairy products. Because agricultural products are increasingly processed in mass quantities and are widely distributed, sometimes globally, large numbers of people could potentially be exposed to EHEC. One hamburger patty may contain the meat of several animals from four different countries. One beef carcass ground for hamburger can contaminate 8 tons of finished ground beef.
The Centers for Disease Control and Prevention (CDC) has issued the recommendation that all stool specimens submitted for culture include detection of Shiga toxins. Beginning in August 2007, MuirLab will routinely screen all stool culture specimens for Shiga toxin, in addition to Salmonella, Shigella and Campylobacter spp. The method used will be a rapid immunochromatographic test. Those specimens that test positive for either or both Shiga toxin 1 and 2 will be further processed for isolation of STEC, with confirmation by the public health department. The State of California has also added Shiga toxin to its list of reportable diseases.