Performance of Antigen Detection Tests for SARS-CoV-2 in Ghana

Abstract

RT-PCR, the gold standard for SARS-CoV-2 detection, remains expensive and requires highly trained laboratory personnel, which proves to be a challenge in resource-limited settings. Antigen-based rapid diagnostic tests (Ag-RDTs) are cheaper and have a short turnaround time, which is important in providing results for the identification and isolation of infected persons. However, independent evaluation of the holistic diagnostic performance of Ag-RDTs, including detection of variant-specific infection, is limited and necessitates this evaluation. We tested 268 nasopharyngeal specimens using RT-PCR and Ag-RDTs [Flourescence Immunoassay (FIA) and Lateral Flow Immunoassay (LFIA)] to detect SARS-CoV-2 infections, followed by viral load quantification. Variant identification was done using a PCR-based assay. Generally, FIA has higher sensitivity, positive predictive value, and accuracy than LFIA. However, LFIA has a higher specificity and negative predictive value than FIA. There was a strong agreement between the Ag-RDTs and RT-PCR. In asymptomatic cases, FIA has a higher sensitivity, PPV, and accuracy than LFIA. Furthermore, both Ag-RDTs had 100% sensitivity in cases with high viral load (Ct <25). Although sensitivity is reduced at low viral loads (Ct >30), FIA has higher sensitivity than LFIA. In infections associated with the Alpha variant, FIA has better sensitivity than LFIA, and vice versa for Delta variant infections. However, both Ag-RDTs have 100% sensitivity for detecting Omicron infections. Ag-RDTs performed well with respect to the WHO criteria for antigen test usage and offer prospects of increased testing capacity in a pandemic at a relatively low cost. Both Ag-RDTs perform excellently in patients with high viral loads and infections associated with the Omicron variant relative to the other VOCs (Alpha and Delta variants). However, FIA has better sensitivity in asymptomatic patients. Notwithstanding this, results should be interpreted in conjunction with other clinical parameters.