Health officials say two people infected with coronavirus in California died as many as three weeks before the US reported its first death from the disease in late February,
It's a gap that underscored the shortcomings in the nation's surveillance system for detecting outbreaks.
The deaths in early and mid-February show that the virus was spreading in California well before officials realised that outbreaks were underway in at least two parts of the country at about the same.
Officials in northern California's Santa Clara County said the two people died at home on Febraury 7 and Febraury 18, neither had travelled outside the country to coronavirus hotspots.
Due to the virus taking one to two weeks between the time people are infected and when they become sick enough to die, the earlier death suggests that Covid-19 was circulating in the area in late January.
Previously, the first infection reported anywhere in the US was in Seattle on January 22 while the first known death was in Washington state on March 1 before officials attributed two deaths from February 27 to the virus.
"What there deaths tell us is that we had community spread probably to a significant degree far earlier than we had known,: said Dr Sara Cody, Health Director of Santa Clara County.
"That indicated that the virus was probably introduced and circulating in our community, again, far earlier than we had known."
The infections in the two patients were confirmed by way of post-mortem tissue samples that were sent to the US Centres or Disease Control and Prevention.
Thousands of travellers from China and other affected regions entered the US before the travl bans and airport screenings were put in place by the Trump administration in min to late January.
Lack of widespread testing means the country was flying blind to the true number of coronavirus infections.
Covid-19 causes mild to moderate symptoms for most people, but for some who are especially older adults or people with exsisting health problems, it can cause a more severe illness.
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