Since 1982, several outbreaks of hemorrhagic colitis due to EHEC, or E coli O157:H7, have occurred in the United States and other parts of the world. Contaminated, undercooked ground beef has been most frequently implicated in the outbreaks, although unpasteurized dairy products and other foods have also been the source of infection in sporadic cases. The most common clinical manifestation of EHEC infection is abdominal cramps and watery, bloody diarrhea. HUS secondary to the initial colitis develops in about 10% of patients under 10 years of age. Definitive diagnosis is made by isolation and identification of EHEC in stool samples. Treatment focuses on rehydration and supportive therapy. The use of antimicrobial agents, narcotics, or antimotility agents is not recommended, because they neither shorten the course of illness nor prevent the development of sequelae.