2.2 Sample collection
A total of 3160 swab samples were collected between September to December of 2019 in 14 provinces of China (including Hubei), mainly for routine surveillance on avian diseases, such as avian influenza viruses (AIV), Newcastle disease viruses (NDV), etc. The swab samples were collected through taking smears at both cloacal and oropharyngeal tracts of a bird, and stored in 1.5 mL phosphate buffered saline (PBS, pH 7.2) containing 10% glycerol. The RNA was extracted using an RNeasy Mini Kit (Qiagen, Hilden, Germany) following manufacturer’s instructions, and stored at -80°C.