Federal scientists have found evidence that the coronavirus was likely present on the West Coast a month before the earliest known date the pathogen is currently thought to have circulated in the U.S.
Scientists with the Centers for Disease Control and Prevention released a study Tuesday that found coronavirus antibodies in 106 samples of donated blood collected by the Red Cross in the U.S. last December and January.
Previously, the earliest known cases of COVID-19 were detected by public health agencies between Jan. 21 and Feb. 23. The first confirmed case in the U.S. was identified in Washington state on Jan. 20. The first confirmed Bay Area case was a resident of Santa Clara County, who fell ill on Jan. 31.
The CDC found the antibodies in 39 blood samples from California, Oregon and Washington state, taken between Dec.13 and Dec. 16, 2019, suggesting the virus was circulating before then.
Charles Chiu, who studies infectious diseases at UCSF, categorized the study as “strong” but said some of the samples could represent false positives.
He pointed out that the presence of antibodies for SARS-CoV-2, the pathogen that causes COVID-19, does not automatically mean a person was infected with the coronavirus; it’s possible that some people have preexisting antibodies for it.
Chiu said only two of the samples “have very, very strong or close to definitive evidence that they were derived from a person who was infected.”
“The take-home message from the study is that there probably were a few infections that were really due to SARS-Cov-2, in December and January,” Chiu said. “But the cases were still very, very rare.”
The study was unable to determine if the cases originated overseas or from communities along the West Coast.
—Kevin Stark (@StarkKev)