Escherichia coli O157:H7 (E. coli O157:H7) is one of hundreds of strains of the bacterium Escherichia coli (E. coli). Although E. coli of many types live in the intestines of healthy humans and animals, this strain produces a powerful toxin and can cause severe illness.
Most illness has been due to eating undercooked ground beef. Other cases have been traced to drinking unpasteurized apple juice/cider, raw milk, eating produce contaminated by animal feces, and recreational exposure in contaminated water. Person-to-person contact in families and childcare centers due to poor personal hygiene and inadequate hand washing can cause further transmission.