Update on Escherichia coli O157:H7.

Escherichia coli O157:H7 infection is one of the more intriguing emerging infectious diseases of the industrialized world. The clinical importance of this organism first came to light in the 1980s and has been associated with significant morbidity and mortality in the United States. The infection is more common in industrialized countries than developing ones and is most closely associated with asymptomatic colonization of cattle. Fecal oral transmission is the rule, with the inoculum needed for infection much smaller than that required for E. coli-related travelers' diarrhea. The organism can survive for months in the environment, and cross contamination is common. Watery diarrhea that progresses to bloody diarrhea without prominent fever is the classic presentation. The classic biopsy finding is similar to that of ischemic colitis, with acute inflammation and hemorrhage involving the superficial mucosa with preservation of the deeper crypts. E. coli O157:H7 has powerful Shigella-like toxins that are encoded by bacteriophages and can trigger thrombotic complications such as the hemolytic uremic syndrome or thrombotic thrombocytopenic purpura. The very young and the elderly are most at risk for serious disease and complications. Treatment with antibiotics has been reported to increase the risk for complications, but the evidence supporting this conclusion is unconvincing, with many variables affecting outcome in any one patient.