At least seven people in five US states were infected with the novel coronavirus weeks before those states reported their first cases, a new government study showed.
Participants who reported antibodies against SARS-CoV-2 were likely exposed to the virus at least several weeks before their sample was taken, as the antibodies do not appear until about two weeks after a person has been infected, the researchers said.
The latest results build on findings from a Centers for Disease Control and Prevention study that suggested the novel coronavirus may have been circulating in the United States last December, well before the first Covid-19 case was diagnosed on Jan. 19, 2020.
The positive samples came from Illinois, Massachusetts, Mississippi, Pennsylvania and Wisconsin, and were part of a study of more than 24,000 blood samples taken for a National Institutes of Health research program between Jan. 2 and March 18, 2020.
Samples from participants in Illinois were collected on Jan. 7 and Massachusetts on Jan. 8, suggesting that the virus was present in those states as early as late December.
"This study allows us to uncover more information about the beginning of the US epidemic," said Josh Denny, one of the study authors.
The findings were published in the journal Clinical Infectious Diseases.