Limited Specificity of Serologic Tests for SARS-CoV-2 Antibody Detection, Benin

Abstract

We used commercially available ELISAs to test 68 samples from coronavirus disease cases and prepandemic controls from Benin. We noted <25% false-positive results among controls, likely due to unspecific immune responses elicited by acute malaria. Serologic tests must be carefully evaluated to assess coronavirus disease spread and immunity in tropical regions.

Keywords: Benin; COVID-19; SARS; SARS-CoV-2; West Africa; coronavirus; coronavirus disease; malaria; parasites; respiratory infections; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Serologic diagnostics of SARS-CoV-2 and co-existing pathogens in Benin. A) SARS-CoV-2 ELISA reactivity by using different commercially available assays in prepandemic controls from 2019 and SARS-CoV-2 RT-PCR-confirmed patients from 2020. Dashed lines denote the ratio thresholds of >1.1 (positive) and <0.9 (negative); results between these values are considered borderline, as defined by the manufacturers, EUROIMMUN (https://www.euroimmun.com) and InBios (https://inbios.com). Solid line denotes mean ELISA reactivity. B) SARS-CoV-2 PRNT₅₀ in prepandemic controls from 2019 and SARS-CoV-2 RT-PCR–confirmed patients from 2020, shown in log₁₀ scale for clarity. Solid line denotes mean PRNT log₁₀ titer. C) Percentage of prepandemic controls with Plasmodium parasitemia who were SARS-CoV-2 ELISA–positive versus those who were SARS-CoV-2 ELISA-negative, shown in log₁₀ scale for clarity. Solid line denotes the mean copies/mL. Asterisk denotes p<0.05. D) ZIKV ELISA IgG ELISA percent seropositivity and ZIKV ELISA reactivity within SARS-CoV-2–positive and SARS-CoV-2–negative prepandemic controls. Continuous line denotes the mean ELISA reactivity. Asterisk denotes p<0.05. E) ZIKV PRNT₅₀ results. Continuous line denotes the mean PRNT₅₀ log₁₀ reactivity. NS, not statistically significant; PRNT₅₀, 50% plaque reduction neutralization test; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; ZIKV, Zika virus.

Figure 2

Molecular and serologic test results for betacoronaviruses and co-existing pathogens in Benin. Individual results are shown for reactivity of different commercially available SARS-CoV-2 ELISAs, SARS-CoV-2 PRNT, and IFA reactivity to common cold human coronaviruses OC43 and HKU1 in prepandemic controls from 2019 and SARS-CoV-2 RT-PCR confirmed patients from 2020; EBV PCR, CMV PCR, and 3 EBV ELISAs (EBV-CA IgM, EBV-CA IgG, and EBV-EBNA IgG) from the same groups; and ZIKV-IgG ELISA, ZIKV-PRNT, and malaria PCR from the same groups. Gray squares denote positive results; black squares denote inconclusive results; and white squares denote negative results. Dash (–) denotes samples in which the assay was not performed due to low sample volume. β-CoVs, betacoronaviruses; CA, viral capsid; CMV, cytomegalovirus; DPD, days the serum sample was taken after positive RT-PCR SARS-CoV-2 diagnosis; EBNA, nuclear antigen 1; EBV, Epstein-Barr virus; IFA, immunofluorescence; PRNT₅₀, 50% plaque reduction neutralization test; RT-PCR, reverse transcription PCR; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; ZIKV, Zika virus.