A small number of COVID-19 infections appear to have occurred in the U.S. several weeks before public health officials identified the first cases. More analysis is needed, but the timeline is being accepted by more health officials, The Associated Press reported.
“The studies are pretty consistent,” Natalie Thornburg, PhD, the principal investigator for the CDC’s respiratory virus immunology team, told the news service.
“There was probably very rare and sporadic cases here earlier than we were aware of,” she said. “But it was not widespread and didn’t become widespread until late February.”
The first U.S. infection was identified on Jan. 20, 2020, after a man in Washington state returned from travel to Wuhan, China, on Jan. 15 and visited a health clinic on Jan. 19, the AP reported. The CDC has said the U.S. outbreak started between mid-January and early February, though the new research points to a handful of earlier cases.
The latest study, which was done by the National Institutes of Health and published Tuesday in the medical journal Clinical Infectious Diseases, looked at blood samples from more than 24,000 people in the U.S. that were collected between January and mid-March 2020. The research team looked for antibodies that could indicate previous coronavirus infection.
Seven people -- three in Illinois and one each in Massachusetts, Mississippi, Pennsylvania, and Wisconsin -- were infected earlier than COVID-19 cases were originally reported in the five states. One of the Illinois cases could have happened as early as Christmas Eve, the researchers said
The analysis isn’t definitive because the antibodies for COVID-19 appear similar to antibodies for other coronaviruses, the AP reported. To lessen false positive results, the NIH researchers used multiple tests that look for COVID-19 antibodies that bind to different parts of the virus. The team plans to release more information after further analysis, the NIH said in a statement.
The NIH scientists also found it notable that the seven people didn’t live in New York City or Seattle, where the first U.S. outbreaks occurred in 2020.
“The question is how did, and where did, the virus take seed,” Keri Althoff, PhD, the lead study author and an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, told the AP.
“It probably seeded in multiple places in our country,” she said.