These were mostly linked to the Huanan Seafood Wholesale Market, which also sold live animals, and one theory is that the virus came from one of these kinds of animals; or, in other words, has a zoonotic origin.A pneumonia cluster of unknown cause was observed on 26 December and treated by the doctor Zhang Jixian in Hubei Provincial Hospital, who informed the Wuhan Jianghan CDC on 27 December.