The findings significantly strengthen evidence suggesting the virus was spreading around the world well before public health authorities and researchers became aware, upending initial thinking about how early and quickly it emerged.

Scientists at the U.S. Centers for Disease Control and Prevention found evidence of infection in 106 of 7,389 blood donations collected by the American Red Cross from residents in nine states across the U.S., according to the study published online in the journal Clinical Infectious Diseases…

In analyzing the blood samples, the CDC scientists found antibodies in 39 samples from California, Oregon and Washington state collected between December 13 and December 16.

The findings suggest there were isolated cases of coronavirus infection on the U.S. West Coast in mid-December, the scientists wrote.