https://www.mercurynews.com/2020/05/19/coronavirus-stanford-finds-no-covid-19-infections-in-2019-swabs/

As the Bay Area continues to tackle the COVID-19 pandemic, a mystery remains: When did the virus arrive here?

Speculation has been growing that the coronavirus may have been circulating in the region long before we knew it had reached our shores, but a new study out of Stanford suggests it wasn’t sickening people here in 2019.