Experts are investigating how the coronavirus spread through the US – but pinpointing its arrival is nearly impossible

Recently, Washington officials have been looking into the cases of two patients with symptoms typical of Covid-19 in late December, after they recently tested positive for antibodies to the virus. These patients could have suffered from a severe flu or other respiratory illness, and contracted the coronavirus later – but more research and widespread serological tests could help clear up whether some severe cases in late December or January that appeared to be cold or flu were in fact Covid-19.

“Absolutely there’s a chance that there were more infections that resulted in death, at a time when we didn’t know about this novel coronavirus,” said Andrew Badley, chair of the Mayo Clinic’s Covid-19 research task force. “As we do more testing, I think it would be quite likely that we will find cases that go back several months in North America.”

https://www.theguardian.com/world/2020/may/26/us-coronavirus-patient-zero-100000-deaths#maincontent

But much about these early cases is – and will remain – unclear.

Newsom, the California governor, ordered coroners in the state to review autopsies back to December, and the Mayo Clinic is one of many academic medical centers giving cases of pneumonia and flu-like illness a second look. But because only a fraction of deaths at a given medical center are autopsied, and because of the small number of coronavirus infections, even widespread reviews of preserved tissues would not fill in the full picture.

“I mean, we’re not going to exhume bodies and test them,” said George Rutherford, an epidemiologist at the University of California, San Francisco.

A genetic analysis found at least eight lineages of the coronavirus circulating in northern California, suggesting that the virus was introduced to the region several times from different sources. That research has yet to be peer-reviewed and published in a scientific journal, but these early findings support what many epidemiologists believe: that there wasn’t a single “patient zero” who sparked the outbreak in the US.

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