The coronavirus was present in the U.S. weeks earlier than scientists and public health officials previously thought, and before cases in China were publicly identified, according to a new government study published Monday.

The virus and the illness that it causes, COVID-19, were first identified in Wuhan, China, in December 2019, but it wasn't until about Jan. 20 that the first confirmed COVID-19 case, from a traveler returning from China, was found in the U.S.

However, new findings published in the journal Clinical Infectious Diseases suggest that the coronavirus, known officially as SARS-CoV-2, had infected people in the U.S. even earlier.

https://www.npr.org/sections/coronavirus-live-updates/2020/12/01/940395651/coronavirus-was-in-u-s-weeks-earlier-than-previously-known-study-says

This discovery adds to evidence that the virus was quietly spreading around the world before health officials and the public were aware, disrupting previous thinking of how the illness first emerged and how it has since evolved. It also shows the virus's presence in U.S. communities likely didn't start with the first case identified case in January.

Researchers came to this conclusion after the U.S. Centers for Disease Control and Prevention analyzed blood donations collected by the American Red Cross from residents in nine states. They found evidence of coronavirus antibodies in 106 out of 7,389 blood donations. The CDC analyzed the blood collected between Dec. 13 and Jan. 17.

The presence of antibodies in a person's blood means they were exposed to a virus, in this case the coronavirus, and that their body's immune system triggered a defensive response.

Researchers found coronavirus antibodies in 39 samples from California, Oregon, and Washington as early as Dec. 13 to Dec. 16. They also discovered antibodies in 67 samples from Connecticut, Iowa, Massachusetts, Michigan, Rhode Island, and Wisconsin in early January — before widespread outbreaks in those states.