The colonic pathology of Escherichia coli O157:H7 infection.

We report the colonic pathology of two surgical excisions and two autopsies from patients acutely infected by E. coli O157:H7. The right colon was most severely affected. Extreme edema, fibrin deposition, and hemorrhage in the submucosa was the most distinctive finding. All cases showed patchy mucosal ulceration, mucosal hemorrhage, neutrophil infiltration, and microvascular thrombi. Pseudomembranous lesions similar to those described in pseudomembranous colitis caused by Clostridium difficile were a minor feature. Advanced lesions displayed regenerative mucosal changes and heavy plasmacytic infiltration of submucosa. The colonic pathology may be due to bacterial verocytotoxin rather than to bacterial attachment-effacement or invasion.