Evaluation of the Roche antigen rapid test and a cell culture-based assay compared to rRT- PCR for the detection of SARS-CoV-2: A contribution to the discussion about SARS-CoV-2 diagnostic tests and contagiousness

Abstract

Background: The most sensitive method to detect SARS-CoV-2 relies on rRT-PCR; however, viral RNA can be detected weeks/months after clinical resolution. Since rRT-PCR cannot discern between non- and infectious virus, it is unclear whether the presence of viral RNA after recovery reflects infectious SARS-CoV-2. However, recent studies suggest a positive correlation between antigen rapid tests (Ag-RDT) and virus isolation that is more suited to assess contagiousness. Objectives: To assess the utility of SARS CoV-2 diagnostic tests in different settings we evaluated the performance of Ag-RDT-based and a cell-culture-based SARS-CoV-2 assay in comparison to rRT-PCR. Study design : A total of 61 Nasopharyngeal-Swabs tested positive by cobas® SARS-CoV-2 rRT-PCR were in parallel evaluated with the Roche Ag-RDT and a cell culture-based assay to detect SARS-CoV-2. Results: SARS-CoV-2 was successfully isolated in 51/61 samples corresponding to 83.6%, which was 97.3% or 96.2% when considering samples with E-gene Ct-value <25 and <28, respectively. In comparison, the Ag-RDT showed an overall sensitivity of 85.2%, that increased to 100% and 96.2% using an E-gene Ct-value cut-off of <25 and <28, respectively. There was an overall good agreement between the commercial Ag-RDT and our in-house cell culture-based SARS-CoV-2 detection assay. However, SARS-CoV-2 could be isolated from two samples that tested negative by Ag-RDT. Conclusions: Our results support the use of the Roche Ag-RDT to detect SARS-CoV-2 exposure in large scale populations. However, it is recommended to use rRT-PCR, potentially in conjunction with cell culture-based SARS-CoV-2 assay, to support clinicians in making decisions regarding fragile patient groups.

Relationship of SARS-CoV-2 Antigen and Reverse Transcription PCR Positivity for Viral Cultures

“…However, other studies have demonstrated a period of prolonged positivity for RT-PCR testing beyond which virus has been isolated ( 5 , 6 ). Therefore, a comprehensive examination of antigen test performance characteristics in identifying infectious persons who have SARS-CoV-2 infections requires comparison with multiple data points, including RT-PCR test positivity and the ability to isolate the virus (a marker for infectiousness) ( 5 – 7 ). In this study, we expand on a previous report ( 1 ) that examined performance of antigen testing relative to RT-PCR by reporting virus isolation data for persons who had positive results by antigen test or RT-PCR.…”

Why Daily SARS-CoV-2 Nasal Rapid Antigen Testing Poorly Detects Infected and Infectious Individuals

“…These models may overestimate test effectiveness if infectiousness is based only on simulated viral loads in a single, tested specimen type, and/or if the IVLT chosen is similar to the LOD of the simulated test. Additionally, nearly all studies evaluating Ag-RDT concordance with infectiousness performed viral culture only on a single specimen type 20,21,41,46,[48][49][50]63,[65][66][67][68][69][70]88 potentially overlooking infectious virus in other specimen types. One of these studies 65 is cited as basis for CDC 80 recommendations to use of repeat ANS Ag-RDTs to improve the clinical sensitivity of these tests.…”

“…Although many Ag-RDT evaluations have observed relatively high concordance between Ag-RDT results and infectiousness (as established directly by viral culture 21,34,41,46,[48][49][50][63][64][65][66][67][68][69][70] or presumed by quantitative viral loads or semiquantitative Ct values 22,[71][72][73] ), this high concordance may not hold when Ag-RDTs are used for screening testing in the community. For example, in several studies 34,46,48,64,68,[70][71][72][73] most infected participants were already symptomatic by the time sampling began, so Ag-RDT performance would not be generalizable to the early period of infection. A few studies accounted for infection stage and assessed longitudinal performance of nasal swab Ag-RDTs relative to viral culture 41,49,50,63,65,66,70 , although only some 41,49,50,63,65 were designed for prospective sampling that would capture the early period of infection.…”

“…Although many Ag-RDT evaluations have observed relatively high concordance between Ag-RDT results and infectiousness (as established directly by viral culture 21,34,41,46,48-50,63-70 or presumed by quantitative viral loads or semi-quantitative Ct values 22,71-73 ), this high concordance may not hold when Ag-RDTs are used for screening testing in the community. For example, in several studies 34,46,48,64,68,70-73 most infected participants were already symptomatic by the time sampling began, so Ag-RDT performance would not be generalizable to the early period of infection. A few studies accounted for infection stage and assessed longitudinal performance of nasal swab Ag-RDTs relative to viral culture 41,49,50,63,65,66,70 , although only some 41,49,50,63,65 were designed for prospective sampling that would capture the early period of infection.…”

Evaluation of the DiaSorin LIAISON SARS-CoV-2 antigen assay on nasopharyngeal swabs in two different SARS-CoV-2 pandemic waves in Switzerland: The impact of the Omicron variant on its performance

“…Compared to rRT-PCR, the less expensive SARS-CoV-2 antigen detecting assays, commercially available either as rapid or automated high-throughput tests, have a lower sensitivity. However, they have been shown to correlate with a high viral load and the ability to replicate in cell cultures, which seem to indicate contagiousness [ 4 , 5 ]. Therefore, by rapidly and reliably identifying individuals with high viral load, antigen testing has been established to be an easy and efficient diagnostic tool for preventing the spread of infection.…”