Journal
OPEN FORUM INFECTIOUS DISEASES
Volume 7, Issue 9, Pages -Publisher
OXFORD UNIV PRESS INC
DOI: 10.1093/ofid/ofaa387
Keywords
antibody; COVID-19; diagnosis; SARS-CoV-2; serology
Categories
Funding
- New South Wales Government's Office for Health and Medical Research
- Snow Medical Research Foundation
- National Health and Medical Research Council's Australian Partnership for Preparedness Research on Infectious Disease Emergencies
- National Health and Medical Research Council's Centre of Research Excellence in Emerging Infectious Diseases
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Background. Testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibodies has become an important tool, complementing nucleic acid tests (NATs) for diagnosis and for determining the prevalence of coronavirus disease 2019 (COVID-19) in population serosurveys. The magnitude and persistence of antibody responses are critical for assessing the duration of immunity. Methods. A SARS-CoV-2-specific immunofluorescent antibody (IFA) assay for immunoglobulin G (IgG), immunoglobulin A (IgA), and immunoglobulin M (IgM) was developed and prospectively evaluated by comparison to the reference standard of NAT on respiratory tract samples from individuals with suspected COVID-19. Neutralizing antibody responses were measured in a subset of samples using a standard microneutralization assay. Results. A total of 2753 individuals were eligible for the study (126 NAT-positive; prevalence, 4.6%). The median window period from illness onset to appearance of antibodies (range) was 10.2 (5.8-14.4) days. The sensitivity and specificity of either SARS-CoV-2 IgG, IgA, or IgM when collected >= 14 days after symptom onset were 91.3% (95% CI, 84.9%-95.6%) and 98.9% (95% CI, 98.4%-99.3%), respectively. The negative predictive value was 99.6% (95% CI, 99.3%-99.8%). The positive predictive value of detecting any antibody class was 79.9% (95% CI, 73.3%-85.1%); this increased to 96.8% (95% CI, 90.796-99.0%) for the combination of IgG and IgA. Conclusions. Measurement of SARS-CoV-2-specific antibody by IFA is an accurate method to diagnose COVID-19. Serological testing should be incorporated into diagnostic algorithms for SARS-CoV-2 infection to identify additional cases where NAT was not performed and resolve cases where false-negative and false-positive NAFs are suspected. The majority of individuals develop robust antibody responses following infection, but the duration of these responses and implications for immunity remain to be established.
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