Performance characteristics of INDICAID antigen rapid diagnostic test on SARS-CoV-2 Samples During the Omicron wave in Cameroon

Background WHO 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. Methods A 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. Results A 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. Conclusion For 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.