USDA's Food Safety and Inspection Service reported:
FSIS was notified of an investigation of E. coli O157:H7 illnesses by the Wisconsin Division of Public Health on Jan. 10, 2013. Working in conjunction with the Wisconsin Division of Public Health, three case-patients with the outbreak strain have been identified in the state with illness onset dates ranging from Dec. 29, 2012 to Jan. 1, 2013. Among the three case-patients with available information, all three reported consuming raw ground round; two consumed product ground and purchased on Dec. 24, 2012; the third consumed product ground and purchased on Dec. 30, 2012 prior to illness onset.
The colitis caused by Escherichia coli (E. coli) O157:H7 is characterized by severe abdominal cramps, diarrhea that typically turns bloody within 24 hours, and sometimes fever. 
The incubation period—that is, the time from exposure to the onset of symptoms—in outbreaks is usually reported as 3 to 4 days, but may be as short as 1 day or as long as 10 days. [4, 13, 26] Infection can occur in people of all ages but is most common in children. 
E. coli O157:H7 and other Shiga toxin-producing E. coli (STEC) infections can lead to a severe, life-threatening complication called the hemolytic uremic syndrome (HUS). [4, 13]
HUS accounts for the majority of the acute deaths and chronic injuries caused by the bacteria.  HUS occurs in 2-7% of victims, primarily children, with onset five to ten days after diarrhea begins. [23, 44] “E. coli serotype O157:H7 infection has been recognized as the most common cause of HUS in the United States, with 6% of patients developing HUS within 2 to 14 days of onset of diarrhea.” [44, 45] And it is the most common cause of renal failure in children. [26, 45, 48]