According to research undertaken by the Harvard Medical School, the SARS CoV-2 virus already circulated in Wuhan in late summer and early fall of 2019. The research is based on analysis of hospital traffic and search engine data in Wuhan.
Abstract

The global COVID-19 pandemic was originally linked to a zoonotic spillover event in Wuhan’s Huanan Seafood Market in November or December of 2019. However, recent evidence suggests that the virus may have already been circulating at the time of the outbreak. Here we use previously validated data streams - satellite imagery of hospital parking lots and Baidu search queries of disease related terms - to investigate this possibility. We observe an upward trend in hospital traffic and search volume beginning in late Summer and early Fall 2019. While queries of the respiratory symptom “cough” show seasonal fluctuations coinciding with yearly influenza seasons, “diarrhea” is a more COVID-19 specific symptom and only shows an association with the current epidemic. The increase of both signals precede the documented start of the COVID-19 pandemic in December, highlighting the value of novel digital sources for surveillance of emerging pathogens.

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