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When did the coronavirus arrive in the United States?
The first infection was confirmed on January 21, 2020 in a Washington state resident who recently returned from Wuhan, China. Shortly after, experts concluded that the virus had been in the country for weeks.
A study released Tuesday offers new evidence: Based on a blood test analysis, scientists have identified seven people in five states who may have been infected long before the first confirmed cases in those states. The results suggest that the virus may have circulated in Illinois, for example, as early as December 24, 2019, although the first case in that state was confirmed a month later.
But the new study is flawed, some experts said: It failed to adequately address the possibility that the antibodies were to coronaviruses that cause colds, and the results could be an oddity of the tests used. Additionally, the researchers also did not have travel information for any of the patients, which might have helped explain the test results.
“It’s an interesting article because it raises the idea that everyone thinks it’s true, that there were infections that weren’t diagnosed,” said Scott Hensley, an immunologist at the University of Pennsylvania.
But the small number of samples that tested positive made it difficult to ensure that these were real cases of infection and not just a methodological error. “It’s hard to know what is a real signal and what is not,” he said.
If the results are correct, however, they do point to the idea that poor testing in the United States missed most cases in the first weeks of the pandemic.
“Without a test, you can’t see what’s going on,” said Keri Althoff, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health and lead author of the study. “During those first few months in some of those states where we didn’t suspect there were a lot of infections there.”
It’s no surprise that there were undocumented cases early in the pandemic, said Sarah Cobey, an evolutionary biologist at the University of Chicago. Experts “already knew this to be the case by studying trends in excess mortality and hospitalizations,” she said.
Dr. Cobey’s most recent model estimated that there were around 10,000 infections in Illinois on March 1, 2020. “Given the horrific state of the tests, there was no doubt that we were missing most of the tests. early transmissions, ”she added.
In the study, published in the journal Clinical Infectious Diseases, Dr Althoff and his colleagues analyzed blood samples from more than 24,000 people. They found nine people who donated blood between January 2 and March 18 of last year and who appeared to have antibodies to the coronavirus.
Seven of the samples were from blood donated before the date of first diagnosis in their states – Illinois, Wisconsin, Pennsylvania, Mississippi and Massachusetts. The results are consistent with those of another study which anti-coronavirus antibodies identified in blood donated from mid-December 2019.
The participants were enrolled in a long-term National Institutes of Health project called All of us, which aims to include one million people in the United States in order to increase the representation of minorities in research. Only about half of the people in the study were Caucasian.
At the start of the pandemic, the virus would have infected very few people. Low prevalence increases the chances that an antibody test will mistakenly identify a sample as having antibodies when it does not, said Dr Hensley – a false positive.
The researchers attempted to minimize this possibility by using two antibody tests in sequence. The first test reported 147 samples as possibly containing antibodies to the coronavirus; the second reduced that number to nine.
The team also analyzed 1,000 blood samples from the 2018-19 cold and flu season, and found none that tested positive for antibodies to the coronavirus.
“It’s still very possible that some of these are false positives,” said Dr Josh Denny, CEO of All of Us. But “that all of them are false positives seems pretty unlikely with what we have. made”.
Researchers said they plan to contact participants to ask questions about travel history and will continue to analyze additional samples to estimate when the coronavirus reached U.S. shores.
“The exact month he likely entered the United States is still unknown,” Dr Althoff said. “It’s basically a puzzle right now, and our study is just one piece of that puzzle.”
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