Some cases of unexplained pneumonia have been reported as early as December 2019 onwards. Because winter and spring are inherently high seasons for respiratory infections, cases were initially circulated and may have been assumed to be other respiratory illnesses, such as colds and flu. Only when there is a clustered outbreak can they be linked together. In the 7th edition of the diagnostic and treatment program, it is specifically clarified that aggregated outbreaks, i.e., cases with similar symptoms in the same office, the same class in a school or the same family within 2 weeks, may be infectious diseases. The earliest report of such an aggregated outbreak in Wuhan was from December 2019 onwards. But earlier disseminated cases, or the real source i.e. Patient Zero, could also be earlier than December. However, due to the lack of definitive evidence, it is now impossible to find respiratory secretion samples or blood samples from that time to draw definitive conclusions. Content source: Dr. Yurai