Coronavirus spread in California weeks earlier than first thought and early deaths were likely mistaken for the flu, according to local US health officials.

Key points: California has identified a COVID-19 death from early February

California has identified a COVID-19 death from early February A February 29 death was thought to be first US fatality

A February 29 death was thought to be first US fatality The California Governor has ordered health authorities to search for possible cases dating back to December

A 57-year-old woman died of COVID-19 on February 6, far earlier than any other reported cases in the United States, said Santa Clara County health officer Sara Cody.

It was previously thought that the first US death from the disease was in Washington state on February 29.

The details of the deaths could help public health officials better understand how the outbreak took hold in the United States.

Additional early deaths may also be discovered in California after Governor Gavin Newsom said he asked medical examiners from across the state to search for deaths that might have been caused by coronavirus as far back as December.

California Governor Gavin Newsom has ordered testing for coronavirus as far back as December, 2019. ( AP: Rich Pedroncelli )

The California woman's death and two other early deaths — on February 17 and March 6 — were confirmed to have been COVID-19 by US health authorities.

Santa Clara County had previously identified its first case of community transmission on February 28, Dr Cody said.

But none of the three patients who died before February 28 had travelled.

"What these deaths tell us is that we had community transmission, probably to a significant degree, far earlier than we had known," Dr Cody said.

Because the region was going through a bad flu season at the time, many cases may have been misclassified as influenza, she said.

Dr Cody said the cases were likely "iceberg tips", indicating that many more people were also infected.

The first coronavirus death in the US was weeks earlier than first thought. ( Reuters: Patrick T Fallon )

The three cases were discovered because the county medical examiner's office was not satisfied it had found the correct cause of death, Dr Cody said.

Because coronavirus tests were not available, they county saved tissue samples, which they sent to the US Centers for Disease Control.



The criteria at the time by the CDC restricted testing to individuals with a known travel history and who sought medical care for specific symptoms.

Coronavirus deaths in the US topped 46,000 on Thursday, doubling in a little over a week.

The US has by far the world's largest number of confirmed coronavirus cases at more than 830,000.

Reuters