Wisconsin epidemiologists detected a cluster of E. coli O157:H7 cases. The health department interviewed case-patients and found a common exposure. All victims had eaten ground beef from Emmpak, a meat producer. The same strain of E. coli O157:H7 was isolated from the ground beef. The case investigation resulted in a 2.8 million pound recall of Emmpak meat and resulted in related illnesses in at least six states. The responsible Emmpak plant was closed for inadequate sampling and testing procedures.