Viable Severe Acute Respiratory Syndrome Coronavirus 2 Isolates Exhibit Higher Correlation With Rapid Antigen Assays Than Subgenomic RNA or Genomic RNA

Abstract

Background: Rapid identification and effective isolation are crucial for curbing the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). To meet this requirement, antigen-detection rapid diagnostic tests (Ag-RDTs) are essential.Methods: Between February 2020 and August 2020 we performed a cohort study of patients with confirmed COVID-19. The clinical performance of Ag rapid fluorescence immunoassay (FIA) and Ag Gold was evaluated and compared in parallel with genomic and subgenomic real-time reverse transcription-polymerase chain reaction (rRT-PCR) and cell culture-based assays.Results: In total, 150 samples were tested. Of these, 63 serial samples were obtained from 11 patients with SARS-CoV-2 and 87 from negative controls. Serial respiratory samples were obtained 2 days prior to symptom onset (-2) up to 25 days post-symptom onset. Overall, for rRT-PCR-positive samples (n = 51), the detection sensitivity of Ag rapid FIA and Ag Gold was 74.5% and 53.49%, respectively, with a specificity of 100%; however, for samples with low cycle threshold (Ct) values, Ag rapid FIA and Ag Gold exhibited a sensitivity of 82.61% (Ct ≤ 30, 5.6 log10RNA copies/mL) and 80% (Ct ≤ 25, 6.9 log10RNA copies/mL), respectively. Despite low analytical sensitivity, both Ag-RDTs detected 100% infection in cell culture-positive samples (n = 15) and were highly effective in distinguishing viable samples from those with subgenomic RNA (66.66%). For both Ag-RDTs, all samples that yielded discordant results (rRT-PCR + ve/Ag-RDT -ve) were also negative by culture.Conclusion: The data suggest that Ag-RDTs reliably detect viable SARS-CoV-2; thus, they may serve as an important tool for rapid detection of potentially infectious individuals.

SARS-CoV-2 viral load and shedding kinetics

“…1). Indeed, most studies on Ag-RDT detection show good concordance with RT-PCR positivity when Ct values are below 25-30, a viral load compatible with the presence of infectious virus, whereas higher Ct values give less reliable results 34,[37][38][39][40][41] .…”

COVID-19 isolation strategies: What have we learned

“…A study showed that antigen-based RDTs detected 100% of infection in 15 cell culture-positive samples (n = 15) and were 66.7% effective in distinguishing viable samples from those with subgenomic RNA. In addition, discordant samples with positive RT-PCR but negative RDT were actually culture negative [ 36 ]. Based on the sample, it was found that nasopharyngeal swabs were more sensitive than nasal swabs using RDT with 100% and 98.7% sensitivity, respectively [ 37 ].…”

Avoiding False-Positive SARS-CoV-2 Rapid Antigen Test Results with Point-of-Care Molecular Testing on Residual Test Buffer

“…Ag-RDT positive results have been associated with the ability to culture SARS-CoV-2 in vitro or viral loads consistent with a transmissible virus. Therefore, Ag-RDTs have been used as a surrogate for SARS-CoV-2 communicability ( 5 – 9 ). Nova Scotia was the first Canadian province to implement Ag-RDTs for self-perceived asymptomatic individuals in low-barrier volunteer-led community testing centers, to identify individuals at high risk of transmitting SARS-CoV-2 that might otherwise have gone unnoticed ( 10 , 11 ).…”