PRE-PANDEMIC SARS-CoV-2 SEROPOSITIVITY among PREGNANT WOMEN-ZAMBIA, 2017-2018

ABSTRACT

Background: Reliable serologic assays are needed to accurately measure prevalence of prior exposure to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, several countries in Africa have reported apparent SARS-CoV-2 assay cross-reactivity with other non-coronavirus pathogens. We used 3 SARS-CoV-2 serologic assays to assess positivity in archived serum specimens collected in Zambia prior to the COVID-19 pandemic and explored seropositivity associations with participant characteristics. Methods: SARS-CoV-2 antibody seropositivity was measured using serum specimens collected from pregnant women aged 15-49 years enrolled in an HIV and syphilis sentinel surveillance study in 26 sites across Zambia during 2017-2018. Of 9,508 participants with archived specimens, 1,500 (16%) were selected using stratified random sampling (by study site). SARS-CoV-2 antibody seroprevalence was measured using the Panbio IgM/IgG lateral flow assay, Euroimmun spike IgG enzyme-linked immunosorbent assay (ELISA), and the Wantai pan-Ig ELISA. HIV and syphilis testing followed the national testing algorithms. We compared age group and HIV and syphilis status with SARS-CoV-2 antibody seropositivity using chi-square test. Results: Among the 1,500 female participants, 1,297 (86%) had specimens available for testing. Participants' median age was 25 years (interquartile range 21-30 years). HIV and syphilis prevalence were 16% and 6%, respectively. SARS-CoV-2 antibody seropositivity was 14% on the Panbio assay, 7% on the Euroimmun assay, and 2% on the Wantai assay. There was no concordance of positive results between the 3 assays, and no association between SARS-CoV-2 antibody seropositivity and age group, HIV status, or syphilis status on all 3 assays (p>0.05 for all comparisons). Conclusion: Three SARS-CoV-2 serologic assays showed antibody positivity in pre-pandemic specimens, possibly indicating cross-reactivity with antibodies to other coronaviruses or other non-coronavirus pathogens. Panbio and Euroimmun assays yielded more false positives than would be expected based on manufacturer-reported specificities. Although there was no association of SARS-CoV-2 antibody seropositivity with HIV or syphilis, testing for other pathogens could provide information about the identities of cross-reacting antibodies with these assays. Assessing for virus neutralizing capability of cross-reacting antibodies in SARS-Cov-2 antibody positive specimens could provide information about possible pre-existing SARS-CoV-2 immunity.