New USDA testing with substitute H5N1 bird flu virus reminds us why eating rare burgers can be risky CNNUSDA experiments suggest H5N1 not viable in properly cooked ground beef University of Minnesota Twin CitiesAre your burgers safe from bird flu? USDA offers cooking safety tips for Memorial Day USA TODAYProperly cooked hamburgers pose no bird flu risk, US study finds ReutersWell-Cooked Burgers Safe From Bird Flu Virus, Study Finds Forbes