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

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 IgG/IgM rapid diagnostic test (RDT; Genrui Biotech Inc., Shenzhen, China) against an enzyme-linked immunosorbent assay (ELISA), which serves as the gold standard. This cross-sectional study was conducted 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 (DIATHEVA S.r.l., Fano, Italy). 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’s κ=0.22). Positive and negative predictive values (PPVs and NPVs) were 94% and 26%, respectively. 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 serosurveys or post-vaccine response assessments.