Enterohemorrhagic Escherichia coli (EHEC) are specific strains of E. coli responsible for bloody diarrhea and a hemolytic uremic syndrome (HUS).

EHEC first came to attention in 1982, when the investigation of 2 outbreaks in Oregon and Michigan identified a new serotype, O157:H7. EHEC differs from other E. coli strains by producing toxins that play an important role in pathogenesis and are similar to those of Shigella dysenteriae. Hence, EHEC are also known as Shiga toxin-producing E. coli (STEC).

They account for 0.8%-3% of all cases of diarrhea in the United States and a higher percentage of bloody diarrheas (15%-36%).

The incubation period is 3-4 days. Most EHEC cases are due to ingestion of contaminated food or water. Cattle are the major reservoir. Human transmission occurs by ingestion of undercooked beef, raw milk, or other products contaminated by the intestinal contents of cattle. Contaminated vegetables (eg, romaine lettuce) have also been identified as sources of outbreaks. Occasional cases of contaminated water have also been reported. It is estimated that the infectious dose of E. coli O157:H7 is only 10-100 organisms.

Mortality is 1%-2% overall.

HUS is the feared complication of EHEC infection, occurring in 9% of cases. It is characterized by acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. It is more common in children under the age of 10 years.