In 2013, an influenza virus began circulating among poultry in China. It caused several waves of human infection and as of late July 2017, nearly 1,600 people had tested positive for avian H7N9. Nearly 40 percent of those infected had died. In 2017, a medical researcher received a sample of H7N9 virus isolated from a patient in China who had died of the flu. He and his research team subsequently began work to characterize and understand it.