<![CDATA[Coronavirus: Covid-19 in US earlier than first thought, and why that's important to know]>

When Patricia Dowd, a 57-year-old auditor at a Silicon Valley chip maker, died on February 6, her death was a mystery. She'd developed flu-like symptoms but was already on the mend and working from home in San Jose, California; her daughter found her dead in her kitchen.

After flu tests came back negative, the coroner could only determine that she had probably suffered a heart attack " until Tuesday, when the Santa Clara County medical examiner announced that a postmortem tissue sample from Dowd came back positive for coronavirus.

Postmortem tests of Dowd and one other Santa Clara resident " a 69-year-old man who died on February 17 " have shown both were infected with the novel coronavirus. Their cases, combined with a growing pool of antibody test results, are upending what experts thought they knew about the virus's spread in the United States.

Until Tuesday, it was thought that the first coronavirus deaths took place in Washington state, at the end of February. Now, even these newly confirmed cases are not necessarily thought to be the country's very first cases.

What they are, health experts say, is proof that the virus has been present in the United States longer than previously believed.

Dr Peter Chin-Hong, an infectious-disease specialist at the University of California San Francisco, was not surprised by the findings: "California has much more exposure to Wuhan and China than Washington state does. So, it makes sense that patient zero would be here."

"It certainly was around much earlier than we all thought," Chin-Hong said, "and I bet there will be more to come. I expect to find an even earlier case as people investigate more."

Dr Sara Cody, health director of Santa Clara County, said she thought that at least in the Bay Area, the disease was spreading as early as January. "There must have been a somewhat significant degree of community transmission" before the deaths in February, she told The Los Angeles Times. 

Dr Sara Cody, Santa Clara County health director, said she believed the coronavirus was spreading in the Bay Area in January. Photo: Bay Area News Group, via AP alt=Dr Sara Cody, Santa Clara County health director, said she believed the coronavirus was spreading in the Bay Area in January. Photo: Bay Area News Group, via AP

Taken with the findings from a growing body of antibody testing which found Covid-19 antibodies in more than 3,300 Santa Clara residents in April, experts now believe that the disease had an infection rate 50 to 85 times greater than the number of confirmed cases in the county at the time.

While local and state leaders have drawn praise for their early response, California has still seen 37,707 confirmed cases and 1,438 deaths from coronavirus so far.

Findings there are in line with a recent model of the early spread of the disease by researchers at Northeastern University in Boston, shared with The New York Times on Thursday.

The study postulates that by March 1, when there were just 23 confirmed cases in the entire United States, there were already as many as 28,000 infections in the country " including up to 10,700 in New York City and 9,300 cases in the San Francisco Bay Area.

Indeed, on Thursday, New York Governor Andrew Cuomo shared preliminary antibody test results that further suggest Covid-19 has been more widespread in the US than previously thought. In 3,000 tests taken statewide, roughly one of every five New York City residents tested positive for antibodies to the coronavirus, suggesting the virus had spread far more widely than known.

New York has been the state hit hardest by the outbreak, with 263,460 confirmed cases and 15,740 deaths as of Wednesday, most clustered downstate in the New York City metropolitan region. The results also suggested that many New Yorkers who never knew they had been infected " possibly as many as 2.7 million, the governor said " had already encountered the virus, and survived.

This emerging picture of the contagion is sharply at odds with the official US government line. As recently as last week, Dr Robert Redfield, the director of the US Centres for Disease Control and Prevention, told reporters that "through February 27, this country only had 14 cases".

A clear picture of the virus's earliest spread in the United States is vital both to understand the disease and to develop models for treating it. Such models will directly influence federal and state officials' policy decisions " like how soon to reopen businesses.

Early confusion about the disease and its transmission was caused in part by defective testing kits from the Centres for Disease Control and Prevention, as well as strict guidelines limiting who could get tested. Additionally, because January and February were still considered flu season, it made getting a handle on the virus' spread difficult.

Neeraj Sood, a professor at the University of Southern California's Price School of Public Policy, was a co-author of the Santa Clara County study as well as the lead investigator in a similar Covid-19 serology study in Los Angeles County.

"When you start seeing the first death, actually, the number of cases in the population is probably pretty high already. It's been in the community for a long time," Sood told The Los Angeles Times.

Chin-Hong, of UCSF, said that the new information helps public health decision-making going forward in several ways. First, he said, it aids preparation for future pandemics: "In the US for this epidemic, the idea that community spread was happening came way too late, and people had false security that you needed to come from China to have risk " because the CDC said so!"

More immediately, he said, it helps with determining when and how much the pandemic will be under control: "We can still do contact tracing of these folks and maybe check with antibody testing/RNA testing of their contacts who were impacted and might still be infected."

The sooner Americans realise that Covid-19 has been in the US for a long time and infecting far more individuals than first believed, Chin-Hong said, the sooner they can accept "the idea that the virus is universal and not just a Chinese virus".

This article originally appeared on the South China Morning Post (SCMP).

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