A new piece has emerged in the incomplete puzzle of when and how the novel coronavirus, a.k.a. SARS-CoV-2, arrived in the U.S., and it is bound to shift how researchers and the Centers for Disease Control see their timelines for this pandemic.

Autopsies on three individuals who died at home in Santa Clara County show that the earliest known Bay Area death from COVID-19 was a full month earlier than what was previously believed to be the region's first death from the virus. As the Mercury News reports, an individual who died on February 6 posthumously tested positive for COVID-19, and so did a second individual who died at home on February 17.

"Testing criteria set by the CDC at the time restricted testing to only individuals with a known travel history and who sought medical care for specific symptoms," the county said in a statement Tuesday night. "As the Medical Examiner-Coroner continues to carefully investigate deaths throughout the county, we anticipate additional deaths from COVID-19 will be identified."

Reportedly, the CDC has been sent multiple samples taken posthumously from individuals who died in Santa Clara County of flu-like symptoms, and a third individual who died at home on March 6 has also tested positive for the coronavirus.

This revelation shifts the timeline of community spread in the Bay Area — and possibly other parts of the country — significantly. Previously, the first confirmed case of community spread of the virus in the Bay Area was found on February 26, when a woman in Solano County with no known contact with an infected person tested positive. And the first confirmed case of the virus in the Bay Area was found four works earlier, on January 31  — a male patient in Santa Clara County who had recently traveled to Wuhan, China. The second Bay Area case, also in Santa Clara County, was found two days later, a woman who had arrived from Wuhan on January 23 and later began feeling sick.

A death on February 6 with no known contacts with infected people suggests that community spread had been occurring in Santa Clara County weeks earlier (it typically takes several weeks for a patient to develop severe symptoms and die). These autopsy results lend credence to hypotheses that have been publicized recently that the virus may have begun circulating, at least in California, as early as November or December, and a large number of asymptomatic cases, along with the early arrival of flu season, allowed the outbreak to go undetected. Direct flights from Wuhan to both LAX and SFO also could have assisted in bringing the virus to California — and there were still flights from mainland China landing at SFO into mid-February.

And, as the Associated Press reports, these are now the first known U.S. deaths from the coronavirus, with the first previously believed to have been an elderly person in Kirkland, Washington on February 29.

Previously, the first known Californian to die of the virus was a man who had traveled on the Grand Princess cruise ship from SF to Mexico, and he passed away on March 3. Genetic researchers have linked the virus he got — with some certainty — to cases in the Seattle area, and the Seattle outbreak had been dated to mid-January and a "Patient Zero" who had arrived from Wuhan at that time.

This new autopsy evidence suggests that the real Patient Zero in the U.S. likely arrived in California and earlier than the Seattle man.

Recent efforts at antibody prevalence testing — more of which are underway in the Bay Area — suggest the widespread prevalence of the virus in Santa Clara and Los Angeles counties. A Stanford study that released raw results last week found 1.5 percent if people tested had SARS-CoV-2 antibodies — researchers extrapolated from this that between 48,000 and 81,000 Santa Clara County residents could therefore have been exposed to the virus without knowing it. Similar testing in Los Angeles last week suggests that between 220,000 to 442,000 people there may have had the virus.

As the New York Times reported Tuesday, this adds to a growing body of evidence that the actual death rate of the virus is far lower than originally feared, and that the number of mild or asymptomatic cases could, in fact, be huge. We won't know until antibody testing is widespread — and if you're a resident of the Mission District you may be able to get a free antibody test this weekend.

This shifting timeline still does not negate the fact that the virus can be randomly deadly in otherwise young and able-bodied people in ways that the flu is not.

Not including the people who may have died of COVID-19 in February unbeknownst to the CDC, there have been over 44,000 deaths attributed to the coronavirus in the U.S. in just about six weeks. Between 1,600 and 1,800 people are still dying from the virus here every day, though those numbers may be showing signs of slowing. In an average flu season, influenza kills 0.1% of those it infects, or between 20,000 and 60,000 Americans per year, according to the CDC.

Previously: Some Scientists Suggest Undetected Coronavirus Caused California's Oddly Early 'Flu Season'

Photo via UCSF