Performance of anti-SARS-CoV-2 IgG/IgM rapid diagnostic test in N'Djamena, Chad: evidence from a clinical prespective during an outbreak response

Background: The utility of rapid serological tests for anti-SARS-CoV-2 antibodies, particularly in a tropical context, is not well-defined. We evaluated the performance of the GENRUI Biotech Inc IgG/IgM rapid diagnostic test (RDT) against an ELISA as the gold standard. Methods: This was a cross-sectional study in N’djamena, Chad, in July 2022. A total of 198 samples from individuals attending a facility for COVID-19 diagnosis were tested using both the GENRUI RDT and the DIATHEVA COVID-19 IgG ELISA kit. Results: IgG seropositivity with ELISA was 84.8%, significantly higher than the 54% found with the RDT, representing a 30.8% difference. The RDT showed a sensitivity of 60% and a specificity of 80%, with poor agreement with ELISA (Cohen Kappa=0.22). Positive and negative predictive values were 94% and 26% respectively. Conclusions: The rapid IgM/IgG test from GENRUI Biotech Inc. has a significantly suboptimal performance for detecting anti-SARS-CoV-2 antibodies. This highlights the need for performing ELISA on non-reactive RDT cases during sero-surveys or post-vaccine response assessment.