COVID-19 pandemic
2019

The outbreak was discovered in Wuhan in November 2019. It is possible that human-to-human transmission was happening before the discovery. Based on a retrospective analysis starting from December 2019, the number of cases in Hubei gradually increased, reaching 60 by 20 December and at least 266 by 31 December.

A pneumonia cluster was observed on 26 December and treated by Chinese pulmonologist Zhang Jixian. She informed the Wuhan Jianghan CDC on 27 December. After analyzing pneumonia patient samples, a genetic sequencing company named Vision Medicals reported the discovery of a novel coronavirus to the China CDC (CCDC) on 28 December.

On 30 December, a test report from CapitalBio Medlab addressed to Wuhan Central Hospital reported an erroneous positive result for SARS, causing doctors there to alert authorities. Eight of those doctors, including Li Wenliang (who was also punished on 3 January), were later admonished by the police for spreading false rumours. Director of the Emergency Department at the Central Hospital of Wuhan, Ai Fen, was also reprimanded. That evening, Wuhan Municipal Health Commission (WMHC) issued a notice about "the treatment of pneumonia of unknown cause". The next day, WMHC made the announcement public, confirming 27 cases —enough to trigger an investigation.

On 31 December, the WHO office in China was notified about the cluster of unknown pneumonia cases and immediately launched an investigation.

Official Chinese sources claimed that the early cases were mostly linked to the Huanan Seafood Wholesale Market, which also sold live animals. In May 2020, CCDC director George Gao initially ruled out the market as a possible origin, as animal samples collected there had tested negative.
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