Researchers find more evidence virus was inside U.S. in December 2019

Researchers have found more evidence that coronavirus was circulating at low levels in five U.S. states, including Pennsylvania, as early as December 2019 — weeks before the first officially reported cases.

Frozen blood samples show people in the states — including Illinois, Wisconsin, Mississippi and Massachusetts — were infected days or weeks before any virus cases were officially reported in those states.

Volunteers in the National Institutes of Health’s All of Us study, an ongoing effort to gather health information on 1 million people, donated blood as part of the study. Tests of 24,000 samples taken in early 2020 showed antibodies to coronavirus in the blood of at least nine people, the All of Us researchers reported in the journal Clinical Infectious Diseases.

“These included individuals with specimens collected January 7 from Illinois, January 8 from Massachusetts, February 3 from Wisconsin, February 15 from Pennsylvania, and March 6 in Mississippi,” they wrote.

The first previously recognized case of COVID-19 in Illinois was reported Jan. 24 in a woman who had just returned from Wuhan, China, the researchers said.

The first confirmed case in Massachusetts was not until Feb. 1. In Wisconsin, the first confirmed case had been Feb. 5, in Pennsylvania the first reported case was March 6, and in Mississippi it was March 11. It takes about two weeks to develop antibodies after infection, so some volunteers were infected in December, the researchers said.

“This study contributes to the evidence of low-level circulation of SARS-CoV-2 in many states at the start of the U.S. epidemic,” the researchers wrote. “Among the first 12 known cases of SARSCoV-2 infection in the United States, the earliest recognized symptoms onset date was January 14, 2020, and all 12 cases had recently traveled to mainland China or were close contacts of recent travelers. Domestic testing for SARS-CoV-2 began in mid-January 2020.”

At the time. the federal government only recommended testing people with symptoms who had a history of travel, or direct contact with a traveler. These findings suggest that policy missed cases, the researchers said.