COVID-19 may have arrived in the United States as early as December 2019, before the disease was even diagnosed in China, a new study suggests.
The researchers on the study, from the Centers for Disease Control and Prevention (CDC), analyzed more than 7,000 blood donations collected by the American Red Cross in nine states between December 13, 2019 and January 17, 2020.
Of these, 106 samples tested positive for antibodies to SARS-CoV-2, the virus that causes COVID-19.
The findings suggest that “SARS-CoV-2 infections may have been present in the US in December 2019, earlier than previously recognized,” the authors wrote in their paper, published Monday (Nov. 30) in the journal. Clinical Infectious Diseases.
Officials in China first reported a cluster of mysterious cases of pneumonia in Wuhan on December 31, 2019, which turned out to be caused by COVID-19.
In the United States, the first confirmed case of COVID-19 was reported on January 20, 2020 in a Washington state resident who recently traveled to China.
But there is some evidence that the virus was circulating rather than recognized. A case of COVID-19 in China was reportedly traced back to Nov. 17, 2019, Live Science previously reported.
In France, retrospective testing of samples from hospitalized patients revealed a patient infected in late December 2019. And researchers have found SARS-CoV-2 antibodies in blood samples collected in Italy in September, Live Science previously reported.
In the new study, of the 106 samples that tested positive for SARS-CoV-2 antibodies, 39 were collected in California, Oregon and Washington between December 13 and 16, 2019; and 67 were collected in Connecticut, Iowa, Massachusetts, Michigan, Rhode Island and Wisconsin between December 30, 2019 and January 17, 2020.
Positive antibody tests suggest previous infection with COVID-19, but they cannot prove that a person was infected. There is a chance that antibodies to other coronaviruses may “cross react” to give a positive result.
But when the researchers ran additional tests to account for such cross-reactivity, they found that 84 of 90 samples tested had antibodies specific for SARS-CoV-2.
The authors also used a very accurate test for SARS-CoV-2 antibodies. But even very accurate tests will still produce a small number of false positive results.
However, the number of positive results in the new study was higher than would be expected from false positives alone, the researchers wrote.
All in all, these findings “make it highly unlikely that all reactive specimens [positive results] represent false positives, ”the authors concluded.
In other words, at least some of these positives from December 2019 and early January 2020 were likely due to previous COVID-19 infections.
Although the authors tried to measure antibodies specific for SARS-CoV-2, “cross-reactivity with other coronaviruses” cannot be ruled out, said Dr. George Rutherford, professor of epidemiology and biostatistics at the University of California. , San Francisco, told Live Science.
And even if these were true COVID-19 infections, the study can’t determine where the participants contracted the infection – it’s possible that some of the blood donors in the study had recently traveled to China and were infected there, Rutherford noted. (The current study had no information about whether or where the donors had traveled.)
In addition, due to the limitations of the study, the findings cannot reveal how much the virus was circulating at the time.
To confirm the findings, human tissue, saliva, or blood samples from the time should be tested for traces of genetic material from the SARS-CoV-2 virus, the authors said.
Rutherford added that donors may be contacted in future studies, who can provide information about whether they had traveled or had symptoms similar to COVID-19.
This article was originally published by Live Science. Read the original article here.