First US COVID cases may date back to mid-December 2019

SARS-CoV-2 antibodies attacking viruses
SARS-CoV-2 antibodies attacking viruses

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A new National Institutes of Health (NIH) analysis of more than 24,000 stored blood samples reveals SARS-CoV-2 antibodies in nine participants in five states as early as Jan 7, 2020, indicating that COVID-19 was in the country weeks before the Centers for Disease Control and Prevention (CDC) announced the first US case on Jan 21.

Because immunoglobulin G (IgG) antibodies aren't detected until about 2 weeks after infection, the findings date the exposures to late December, although whether the participants were infected in the United States or abroad is unknown.

"Antibody testing of blood samples helps us better understand the spread of SARS-CoV-2 in the U.S. in the early days of the U.S. epidemic, when testing was restricted and public health officials could not see that the virus had already spread outside of recognized initial points of entry," lead study author Keri Althoff, PhD, of Johns Hopkins University, said in an NIH news release.

The study, part of the NIH's All of Us research program, was published today in Clinical Infectious Diseases. The findings are similar to those of a Nov 3, 2020 CDC study in the same journal that identified coronavirus antibodies in blood samples from 7,389 American Red Cross blood donors in nine states as early as mid-December 2019.

High rate of minority patients

In the NIH study, the researchers evaluated 24,079 blood samples collected from adults 18 and older in all 50 states from Jan 2 to Mar 18, 2020 using one of two enzyme-linked immunosorbent assays on the blood samples. They repeated the test using the other assay in the case of a positive result.

Repeat testing was done on the basis of CDC guidance to minimize false-positive results during periods of low virus prevalence. The net sensitivity of the testing protocol was 90.7%, and the specificity was 100%.

Nine participants from outside of the COVID-19 hot spots of Seattle and New York City, which are thought to be the primary sites of coronavirus entry into the United States, tested positive for antibodies. They resided in Illinois, Massachusetts, Mississippi, Pennsylvania, and Wisconsin.

Seven of the nine were older people of Black (five participants) or Hispanic/Latino (two) race. Of all participants who provided blood samples, 57% were women, 49% were White, 24% were Black, and 17% were Hispanic/Latino.

"Although the numbers are limited, these findings reinforce scientific hypotheses of the impact of social factors on viral circulation, including structural discrimination against racial and ethnic minority groups," the researchers wrote.

Seven of the nine were positive for SARS-CoV-2 IgG antibodies before the first confirmed cases in their respective states, with specimens collected on Jan 7 in Illinois, Jan 8 in Massachusetts, Feb 3 in Wisconsin, Feb 15 in Pennsylvania, and Mar 6 in Mississippi. Two seropositive participants reported having been ill with symptoms similar to those of mild COVID-19 but weren't diagnosed due to limited testing capacity; the remaining seven had no mention of illness in their electronic health records.

Importance of early testing

The findings, the researchers said, highlight the importance of rolling out testing as soon as possible after an epidemic is identified. Because early COVID-19 testing was limited to only symptomatic people who had traveled in February or were close contacts of recent travelers, how the virus entered and spread in US communities is unclear.

"Determining the presence and location of SARS-CoV-2 in the earliest days of the US pandemic, together with other information on the spread and severity of COVID-19 illness, is important for understanding of the emergence of the virus, the epidemiology of this virus, and informing simulation models used to predict cases, deaths, and healthcare utilization and subsequently guide future pandemic planning, policy development and resource allocation," the authors wrote.

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