Abstract
COVID-19 Antibody Detecting Rapid Diagnostic Tests (COVID-19 Ab RDTs) are the preferred tool for SARS-CoV-2 seroprevalence studies, particularly in low- and middle-income countries. The present study challenged COVID-19 Ab RDTs with pre-pandemic samples of patients exposed to tropical pathogens. A retrospective study was performed on archived serum (n = 94) and EDTA whole blood (n = 126) samples obtained during 2010–2018 from 196 travelers with malaria (n = 170), schistosomiasis (n = 25) and dengue (n = 25). COVID-19 Ab RDTs were selected based on regulatory approval status, independent evaluation results and detecting antigens. Among 13 COVID-19 Ab RDT products, overall cross-reactivity was 18.5%; cross-reactivity for malaria, schistosomiasis and dengue was 20.3%, 18.1% and 7.5%, respectively. Cross-reactivity for current and recent malaria, malaria antibodies, Plasmodium species and parasite densities was similar. Cross-reactivity among the different RDT products ranged from 2.7% to 48.9% (median value 14.5%). IgM represented 67.9% of cross-reactive test lines. Cross-reactivity was not associated with detecting antigens, patient categories or disease (sub)groups, except for schistosomiasis (two products with ≥60% cross-reactivity). The high cross-reactivity for malaria, schistosomiasis and—to a lesser extent—dengue calls for risk mitigation when using COVID-19 Ab RDTs in co-endemic regions.
Highlights
COVID-19 antibodies confirm current and past infection by SARS-CoV-2 infection
A plethora of COVID-19 Ab Detecting Rapid Diagnostic Tests (COVID-19 Ab RDTs) are marketed—at the time of writing (May, 2021), the diagnostic tracker of the Foundation of Innovative Diagnostics (FIND) lists 213 products [7]; most are lateral-flow immunoassays (LFA) based on a nitrocellulose reagent strip housed in a plastic cassette
Results for the DiaPro IgG and IgM EIA were expressed as a ratio of the sample optical density (OD) 450 nm/620–630 nm and the index values (S/CO, S = ratio of the sample, CO = mean value of three negative controls plus a value of 0.250)
Summary
COVID-19 Ab diagnostics have limited relevance for individual patient care [1,2,3,4], but are valuable at the public health level for seroprevalence studies. Compared to laboratory platforms (enzyme immunoassays (EIA) and chemiluminescence assays (CLIA)), COVID-19 Ab RDTs have simple logistics, require relatively little training, have a short turnaround time, are scalable and are amenable to self-testing. As such, they are preferred tools for seroprevalence studies [5,8,9], despite the fact that the WHO recommends the use of enzyme immunoassays for seroprevalence studies [1]. In low- and middle-income countries (LMICs), COVID-19 Ab RDTs have been deployed for triage, diagnosis and contact tracing [10,11,12]
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