Viral Load-based Evaluation of the Sensitivity of Antigen-based Rapid Detection Assay for SARS-CoV-2

Abstract

Background: Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has become a global public health problem. The real-time reverse transcription-polymerase chain reaction (RT-PCR) is the gold standard test for the detection of SARS-CoV-2. However, the assay requires hours to get the final results. Therefore, antigen-based rapid assays are being used extensively to reduce the time. We have evaluated the performance of the antigen-based rapid test for the detection of SARS-CoV-2 virus in comparison with RT-PCR. Materials and methods: Nasopharyngeal and throat swabs were collected from 366 suspected patients of COVID-19 visiting our institute and subjected to qualitative RT-PCR and antigen-based rapid assays to detect the presence of SARS-CoV-2 virus. The sensitivity and specificity of the antigen-based assay were calculated in comparison with RT-PCR. Results: Compared with RT-PCR, sensitivity and specificity of the antigen-based rapid assay were observed to be 70.5% and 98.6%, respectively, in comparison with RT-PCR. However, the sensitivity of antigen-based rapid assay varied significantly with decreasing viral load. The sensitivity of the rapid antigen assay was equivalent to RT-PCR (23/23, 100%) at a higher viral load (Ct value 15-20). In contrast, the antigen assay could only detect 3/21 (14.28%) samples with Ct value >30. Conclusion:The antigen-based assay could assist in the rapid screening of a large population. However, the rapid antigen assay might not detect early stages of infection represented by low viral load. Therefore, the antigen-based assay could not replace RT-PCR testing. The study reiterates that all antigen-based negative tests should be confirmed by RT-PCR.