ABSTRACT
OBJECTIVES: Antigen rapid diagnostic tests (Ag-RDTs) play an important role in the diagnosis of SARS-CoV-2. They are easier, quicker, and less expensive than the 'reference standard' RT-PCR and therefore widely in use. Reliable clinical data with respect to Ag-RDT performance in SARS-CoV-2 Omicron variants of concern (VOCs) are limited. Consequently, the objective of this study was to determine the impact different VOCs-especially Omicron-have on the clinical performance of an Ag-RDT. METHODS: We compared the clinical performance of the Sofia SARS-CoV-2 Ag-RDT to RT-PCR in a real-world, single-centre study in a clinical point-of-care setting in patients admitted to a large hospital via the emergency department from 2 November 2020 to 4 September 2022. RESULTS: Among 38 434 Ag-RDT/RT-PCR tandems taken, 1528 yielded a SARS-CoV-2 positive RT-PCR test result, with a prevalence of 4.0% (95% CI, 3.8-4.2). Overall sensitivity of the Ag-RDT was 63.7% (95% CI, 61.3-66.1) and overall specificity was 99.6% (95% CI, 99.5-99.6). Ag-RDT sensitivity was dependent on viral load (VL), because the sensitivity increased to 93.2% (95% CI, 91.5-94.6) in samples with a VL > 106 SARS-CoV-2 copies/mL. Furthermore, the Ag-RDT was more sensitive in men, and older patients. Variant-dependent sensitivity assessment showed that the sensitivity was significantly lower in Omicron-VOC (64.1%; 95% CI, 60.5-67.6) compared with SARS-CoV-2 wild-type samples (70.0%; 95% CI, 59,8-78,6) (binomial test; p value < 0.001). Analysing the limits of detection showed a 27 times higher 95% limit of detection for the Omicron-VOC BA.5 compared with the SARS-CoV-2 wild-type. DISCUSSION: Ag-RDT sensitivity for detection of patients with lower VLs and with Omicron-VOC is reduced, limiting the effectiveness of Ag-RDTs. However, Ag-RDTs are still an unreplaceable tool for widely available, quick, and inexpensive point-of-care SARS-CoV-2 diagnostics.
ABSTRACT
The rapid and reliable detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is of high importance for individual patient care and hospital infection prevention. We aimed to evaluate the performance of the Sofia SARS-CoV-2 antigen rapid diagnostic test (Ag-RDT) in comparison to real-time reverse-transcription polymerase chain reaction (RT-PCR). We conducted a prospective, monocentric cross-sectional study in an emergency department of a German university hospital from November 2020 to March 2021. We tested all samples using both Sofia SARS-CoV-2 Ag-RDT and real-time RT-PCR. A total of 7877 patients were included. Overall sensitivity of the Ag-RDT was 62.9% and specificity was 99.4%. Sensitivity varied across study months, whereas specificity remained high. Sensitivity increased to 94.2% in samples with a cycle threshold (Ct)-value ≤25. The Sofia Ag-RDT proved to be a rapid tool to detect samples with high viral loads (Ct-value ≤25) and might thus help to identify infectious patients.