December 3, 2020 -- The SARS-CoV-2 virus, which causes COVID-19, may have arrived in the U.S. by December 2019, even before the first cases were reported in China, according to a new study published Monday in the journal Clinical Infectious Diseases.

The first U.S. cases were identified in January 2020, but blood samples show that some Americans may have been infected before then.

The researchers, who work at the CDC, analyzed more than 7,000 blood donations collected by the American Red Cross in nine states between Dec. 13 and Jan. 17. Among those, 106 samples tested positive for coronavirus antibodies, with at least some positives in all nine states.

“SARS-CoV-2 infections may have been present in the U.S. in December 2019, earlier than previously recognized,” the authors wrote in conclusion.

The first cluster of cases was reported in China on Dec. 31, and the first confirmed COVID-19 case was reported in the U.S. on Jan. 20, but the virus was likely circulating before then, according to Live Science. Several studies that have tested blood samples for antibodies this year have found that the virus may have been in China in November, in France in December and in Italy as early as September 2019, the news outlet reported.

However, infectious disease experts continue to review the data. Positive antibody tests may suggest that someone previously had COVID-19, but they can’t prove that someone was infected, the news outlet reported. In some cases, antibodies against other coronaviruses that are similar to SARS-CoV-2 may “cross-react” with the test and show a positive result.

In this study, the researchers performed additional tests in 90 samples to account for potential cross-reactivity and found that 84 had antibodies specifically for SARS-CoV-2. This indicates that it’s unlikely the samples represent false positives, the authors wrote.

In future studies, researchers may consider testing for viral genetic material in human tissue, saliva and blood samples, the authors added. Blood donors could also be contacted to determine whether they had traveled to China or other countries with early COVID-19 infections, as well as whether they had COVID-19 symptoms around the time they donated blood.

WebMD Health News Brief

Sources

Clinical Infectious Diseases, “Serologic testing of U.S. blood donations to identify SARS-CoV-2-reactive antibodies: December 2019-January 2020.”

Live Science, “COVID-19 may have arrived in US by December 2019.”

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