The diagnosis of E. coli O157:H7 in two brothers in Colorado led to a multistate investigation. Stool samples from the boys were tested using pulse-field gel electrophoresis and found to be genetic matches. The results led investigators to another Colorado case with the same genetic pattern. All three cases reported consuming hamburgers purchased at Wal-Mart. A traceback investigation found the frozen hamburger patties were manufactured by Flander's Provision Company in Georgia and had been distributed to several states. The genetic pattern of the E. coli matched others in a national database. A national investigation led to the recall of over 900,000 pounds of ground beef.