Evaluation of two fluorescence immunoassays for the rapid detection of SARS-CoV-2 antigen—new tool to detect infective COVID-19 patients

Abstract

Background Real-Time Reverse-Transcription Polymerase Chain Reaction (RT-PCR) is currently the only recommended diagnostic method for SARS-CoV-2. However, rapid immunoassays for SARS-CoV-2 antigen could significantly reduce the COVID-19 burden currently weighing on laboratories around the world. Methods We evaluated the performance of two rapid fluorescence immunoassays (FIAs), SOFIA SARS Antigen FIA (Quidel Corporation, San Diego, CA, USA) and STANDARD F COVID-19 Ag FIA (SD Biosensor Inc., Gyeonggi-do, Republic of Korea), which use an automated reader. The study used 64 RT-PCR characterized clinical samples (32 positive; 32 negative), which consisted of nasopharyngeal swabs in universal transport medium. Results Of the 32 positive specimens, all from patients within 5 days of symptom onset, the Quidel and SD Biosensor assays detected 30 (93.8%) and 29 (90.6%) samples, respectively. Among the 27 samples with high viral loads (Ct ≤ 25), the two tests had a sensitivity of 100%. Specificity was 96.9% for both kits. Conclusion The high performance of the evaluated FIAs indicates a potential use as rapid and PCR-independent tools for COVID-19 diagnosis in early stages of infection. The excellent sensitivity to detect cases with viral loads above ~106 copies/mL (Ct values ≤ 25), the estimated threshold of contagiousness, suggests that the assays might serve to rapidly identify infective individuals.

SARS-CoV-2 rapid antigen testing in the healthcare sector: A clinical prediction model for identifying false negative results

“…These numbers can be confirmed by other studies(Dinnes et al, 2021) and compare well with our findings. The manufacturer of Standard F indicates a higher sensitivity and specificity of 93.70% and 99.63% respectively (SD Biosensor, 2021a) which is supported by a study by Porte et al (90.6% and 96.9%)(Porte et al, 2021). These differences between trial and real-world data can be explained with bias due to test application and its evaluation under study conditions.…”

Accuracy of rapid point-of-care antigen-based diagnostics for SARS-CoV-2: an updated systematic review and meta-analysis with meta regression analyzing influencing factors

“…All studies were written in English, except for 3 in Spanish [53, 62, 134], 1 in Turkish [95], and 1 in French [153]. Out of the 196 studies, 26 conducted a case-control study [21, 32, 34, 66, 67, 72, 81, 84, 88-90, 93, 94, 96, 103, 108, 135, 140, 144, 145, 151, 156, 166, 168, 182, 184], while the remaining 168 were cross-sectional or cohort studies. The reference method was RT-PCR in all except 1 study, which used viral culture [135].…”

“…This quite likely results from the on average low viral load in 1 study [49], and the asymptomatic study population in the other [175]. On the contrary, compared to the other studies unusual high sensitivity was found in studies where average viral load was high [45, 84, 144, 145] or participants were mainly within the first week of symptom onset [42, 54, 135].…”

Diagnostic Performance of Six Rapid Antigen Tests for SARS-CoV-2

“…When the viral load decreased with C T values above 25, no test presented a sensitivity greater than 15% except the Vircell automatic reader, which detected 36.4% of the samples with C T values of ≥25. The automatic reading of the fluorescent signal can be more sensitive than visual inspection of some of the RATs, which may account for the higher sensitivity of the Vircell assay for samples with a low viral load ( 17 , 18 ).…”