Study points to possible earlier COVID-19 infections in U.S.

People tour the National Mall in Washington D.C., the United States, on March 13, 2021. (Photo by Ting Shen/Xinhua)

Seven of those samples were seropositive prior to the first confirmed case in the states of Illinois, Massachusetts, Wisconsin, Pennsylvania, and Mississippi, according to a new study.

WASHINGTON, June 16 (Xinhua) -- A new antibody testing study suggested SARS-CoV-2 infections happened in the United States earlier than previously reported.

Researchers of the U.S. National Institutes of Health analyzed more than 24,000 stored blood samples from all 50 U.S. states between Jan. 2 and March 18, 2020.

A health care worker prepares a dose of COVID-19 vaccine at a new vaccination site in the California Polytechnic State University in Pomona, Los Angeles County, California, the United States, Feb. 5, 2021. (Xinhua)

They detected antibodies against SARS-CoV-2 using two different serology tests in nine participants' samples.

Seven of those samples were seropositive prior to the first confirmed case in the states of Illinois, Massachusetts, Wisconsin, Pennsylvania, and Mississippi, according to the study published Tuesday by the Clinical Infectious Diseases journal.

The study is the latest to suggest the coronavirus first appeared in the United States earlier than previously known.