Performance characteristics of INDICAID antigen rapid diagnostic test on SARS-CoV-2 samples during the omicron wave in Cameroon

Abstract

BackgroundWHO recommends the use of COVID-19 antigen rapid diagnostic tests (Ag-RDT) with at least 80 % sensitivity and 97 % specificity. In the era of Omicron variants, we sought to ascertain the performance of the INDICAID™ Ag-RDT compared to real-time PCR (RT-PCR) as the gold standard. MethodsA laboratory-based study was conducted among consenting individuals tested for COVID-19 at the virology laboratory of the Chantal BIYA International Reference Centre, Yaoundé-Cameron. The samples were processed by INDICAID™ Ag-RDT and DaAn Gene real-time PCR according to the manufacturer's instructions, and PCR-results were interpreted as per cycle thresholds (CT). The sensitivity, specificity, positive and negative predictive values (PPV and NVP) of INDICAID™ Ag-RDT were evaluated according to PCR CT-values. ResultsA total of 565 nasopharyngeal swabs were collected from participants (median age [IQR]: 40 [31–75]; M/F sex-ratio was 1.2 and 380 were vaccinated). Following PCR, overall COVID-19 positivity was 5.66 %. For CT < 37, INDICAID™ Ag-RDT sensitivity was 21.9 % (95%CI: [8.3–39.9]), specificity 100 % (95%CI: [99.3–100]); PPV 100 % (95%CI: [59.0–100]), NPV 95.5 % (95%CI: [93.4–97.1]) and kappa = 0.34 (95%CI: [0.19–0.35]). For CT < 25, sensitivity was 100 % (95%CI: [47.8–100.0]), specificity 99.6 % (95%CI: [98.7–99.9]); PPV 94.4 % (95%CI: [51.7–100]), NPV 100 % (95%CI: [99.3–100]) and kappa = 0.83 (95%CI: [0.6–1.0]). COVID-19 sequences generated were all Omicron BA.1 subvariants. ConclusionFor patients infected with high viral loads (CT < 25), INDICAID™ Ag-RDT has high intrinsic (sensitivity and specificity) and extrinsic (predictive values) performances for COVID-19 diagnosis. Due to its simplicity and short turnaround time, INDICAID™ Ag-RDT is, therefore a reliable tool to prevent the spread of COVID-19 at community level in the current era of Omicron subvariants.