Sample collection and virus isolation
We collected oropharyngeal and cloacal swabs of poultry (including chickens, ducks, and geese) from live poultry markets in the Guangdong Province during 2016-2019, which were kept in PBS with penicillin and streptomycin. We also collected swabs or tissue samples from sick or dead poultry in farms. The collected swabs were centrifuged, and 0.2 ml of the supernatant was inoculated into nine to 10-day-old SPF chicken embryos. After 48-72 hours of culture at 37°C, the allantoic fluid was collected, and Hemagglutinin-positive samples were further confirmed.