FSIS has conducted a thorough investigation in response to this outbreak, including traceback of beef patties served on Quarter Pounders at McDonald’s, and evidence does not point to ground beef as the likely source of contamination. FSIS used specific meal information reported by ill people to trace beef patties through the supply chain to the establishment where they were produced and did not identify a beef source. Testing on beef patties by the Colorado Department of Agriculture is complete and all samples were found to be negative for E. coli. FSIS will continue to work closely with federal and state partners.