A new analysis of blood samples from 24,000 Americans taken early last year is the latest and largest study to suggest that the coronavirus popped up in the US in December 2019—weeks before cases were first recognized by health officials. The analysis is not definitive, and some experts remain skeptical, but federal health officials are increasingly accepting a timeline in which small numbers of COVID-19 infections may have occurred in the US before the world ever became aware of a dangerous new virus erupting in China, the AP reports. "The studies are pretty consistent,” says Natalie Thornburg of the Centers for Disease Control and Prevention. "There was probably very rare and sporadic cases here earlier than we were aware of. But it was not widespread and didn't become widespread until late February," says Thornburg, principal investigator of the CDC's respiratory virus immunology team.
The study, published Tuesday online by the journal Clinical Infectious Diseases, is by a team including researchers at the National Institutes of Health. They analyzed blood samples collected in the first three months of 2020 for antibodies. The researchers say seven study participants—three from Illinois, and one each from Massachusetts, Mississippi, Pennsylvania, and Wisconsin—were infected earlier than any COVID-19 case was originally reported in those states. One of the Illinois cases was infected as early as Christmas Eve, said Keri Althoff, an associate professor at the Johns Hopkins Bloomberg School of Public Health and the study's lead author. The researchers have not followed up with study participants yet to see if any had traveled out of the US prior to their infection. Some experts say it's possible the 2019 positives could be the result of infections by other coronaviruses, including some that cause the common cold.
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