Journal
JOURNAL OF INFECTIOUS DISEASES
Volume 223, Issue 8, Pages 1334-1338Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/infdis/jiaa796
Keywords
COVID-19; SARS-CoV-2; serology; seroprevalence
Categories
Funding
- Public Health Ontario
- Canada's COVID-19 Immunity Task Force
- Public Health Agency of Canada
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The study revealed that as time passed, the concentration of antibodies in SARS-CoV-2 positive specimens decreased, while the concentration in negative specimens increased. The association between the two tests also decreased over time, indicating a decline in anti-nucleocapsid antibodies.
We analyzed 21 676 residual specimens from Ontario, Canada collected March-August 2020 to investigate the effect of antibody decline on SARS-CoV-2 seroprevalence estimates. Testing specimens orthogonally using Abbott (anti-nucleocapsid) and Ortho (anti-spike) assays, seroprevalence estimates were 0.4%-1.4%, despite ongoing disease activity. The geometric mean concentration (GMC) of antibody-positive specimens decreased over time (P = .015), and GMC of antibody-negative specimens increased over time (P = .0018). Association between the 2 tests decreased each month (P < .001), suggesting anti-nucleocapsid antibody decline. Lowering Abbott antibody index cutoff from 1.4 to 0.7 resulted in a 16% increase in positive specimens.
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