As early as August 2019
Wuhan resident’s internet searches hint that COVID-19 might have already been circulating locally.

https://medicalxpress.com/news/2020-06-coronavirus-emerged-summer.html

Sample quote

A team led by Elaine Nsoesie at Boston University analyzed 111 satellite images from Wuhan between January 2018 to April 2020, as well as frequently looked up symptoms on the Chinese search engine Baidu.

"A steep increase in volume starting in August 2019" was detected at Wuhan hospital parking lots, "culminating with a peak in December 2019," the authors wrote.

Because queries for the word "cough" rise along with yearly influenza seasons, they also looked for "diarrhea" which is a more COVID-19 specific symptom.

"In August, we identify a unique increase in searches for diarrhea which was neither seen in previous flu seasons or mirrored in the cough search data," the team said.

While respiratory symptoms are the most common hallmarks of SARS-CoV-2 infection, the study suggested that diarrhea "may play an important role in community transmission."

The authors concluded that while they could not definitively confirm that the data they documented was linked to the virus, it supported conclusions reached by other research.

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Edit: The Chinese Communist Party has reacted suspiciously quickly to the above article and called it nothing but propaganda