Serologic Testing of US Blood Donations to Identify Severe Acute Respiratory Syndrome Coronavirus 2 and Other Coronaviruses, December 2019 to July 2020

TL;DR

This study used blood donations to find evidence that SARS-CoV-2 was in the US before the first reported case in January 2020.

Contribution

The study provides early evidence of SARS-CoV-2 presence in the US using serologic testing of blood donor samples.

Findings

SARS-CoV-2 antibodies were detected in blood donations as early as December 2019.

The frequency of confirmed SARS-CoV-2 infections increased over time, matching reported case trends.

Early infections were not detected by commercial anti-S tests, suggesting very recent exposure.

Abstract

The first coronavirus disease 2019 (COVID-19) case in the United States was recognized on 19 January 2020, but the time of introduction of the virus into the United States is unknown. An existing sample cohort was examined for serologic evidence of early severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections.

A repository of 46 120 samples from healthy routine blood donors, representing 46 states and the District of Columbia, was tested for total antibodies to SARS-CoV-2 nucleocapsid (anti-N) using a commercial test. All reactive samples were further tested using an experimental receptor-binding domain (RBD)–specific immunoglobulin G (IgG) enzyme-linked immunosorbent assay. Further testing was also conducted for anti-spike (anti-S) antibodies by commercial tests, experimental anti-S immunologic blocking, and for antibodies to the 4 human cold coronaviruses.

Anti-N reactivity was observed in 92 tested samples (0.2%), 91 of which had adequate volume for further testing; of these, 55 were confirmed positive by anti-RBD. None of these reactive findings were attributable to the other human coronaviruses tested. The confirmed-positive frequency increased over time paralleling patterns observed for COVID-19 cases reported in the United States (in contrast to stable patterns over time for the cold coronaviruses). Nine confirmed positive samples (0.07%) were identified among the 13 364 donations collected between 13 December 2019 and 22 January 2020. None of these early confirmed-positive samples were reactive by commercial anti-S tests suggesting very recent infection.

The samples tested in this study were broadly representative of the United States, and all were from individuals who had successfully donated blood. The antibody-reactive results of this study suggest that SARS-CoV-2 was likely present in the United States before 19 January 2020.

SARS-CoV-2 infections in the US likely occurred before clinical COVID-19 disease cases. SARS-CoV-2 anti-nucleocapsid reactivity was low during the first 3 months (December 2019–March 2020), increased 10-fold in the following 3 months, and unrelated to the common cold coronaviruses.

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