The Connecticut Department of Public Health was notified about four laboratory confirmed cases of E. coli O157:H7 infection in residents of New Haven County. Additional case-finding was conducted, and with this effort, a total of eight cases had then been found. A case control study indicated that there was an increased risk of illness associated with drinking a specific brand of fresh apple cider. After completion of the case-control study, six additional patients were identified; these persons had drunk the same brand of apple cider. The Centers for Disease Control laboratory analyzed the E. coli isolates and found them to be closely related using the pulsed-field gel electrophoresis technique, a genetic fingerprinting technique. An advisory was issued to discard or boil the apple cider before drinking. The cider had been sold in various retail outlets. The cider was pressed at a mill in a residential area from apples purchased from multiple sources. Some of the apples used were "drop" apples (i.e., apples picked up from the ground). All apples were brushed and washed in potable municipal water in a flow-through wash system before pressing in a wooden press. Potassium sorbate 0.1% was added as a preservative; the cider was not pasteurized.