in september 2000, an outbreak of escherichia coli gastroenteritis occurred in pennsylvania. patients developed diarrhea within 10 days of visiting the farm. although the clinical presentation varied among the patients, the illness typically began with severe abdominal cramps and nonbloody diarrhea. stool became grossly bloody in day 2 or 3 of illness. most patients became asymptomatic within 1 week; however, approximately 7% of the children with gastroenteritis developed acute renal failure, hypertension, and seizures. which organism was most likely responsible for these infections?