Experts say that means the coronavirus was present in the country weeks earlier than scientists and health officials had previously thought.
Scientists say that an analysis of blood donations shows that the virus may have been spreading across the country as early as 13 December.
Authorities had believed that the earliest recorded case of the virus in the US was 21 January, in a traveller returning from China.
Experts from the US Centers for Disease Control and Prevention looked at blood samples taken by the American Red Cross from 13 December 2019 to 17 January 2020.
All 7,389 samples, which were collected in nine states, were tested for virus antibodies, according to the study published in the journal Clinical Infectious Diseases.
Of those samples at least 106 were discovered to have antibodies for SARS-CoV-2, the scientific name for Covid.
These included samples collected from California, Oregon and Washington between 13 December and 16 December.
“SARS-CoV-2 infections may have been present in the US in December 2019, earlier than previously recognized,” wrote the study’s authors.
More than 13.9 million cases of coronavirus have now been recorded in the US since the pandemic began with more than 275,000 deaths.
