SARS-CoV-2 rapid diagnostic tests for emerging variants

Abstract

SARS-CoV-2 antigen-detecting rapid diagnostic tests (Ag-RDTs) provide laboratory-independent results at the point of care and are powerful tools for public health interventions. Clinical and analytical studies, published in 2021, showed SARS-CoV-2 Ag-RDT detection thresholds related to the presence of infectious virus in symptomatic SARS-CoV-2 infections.1Nordgren J Sharma S Olsson H et al.SARS-CoV-2 rapid antigen test: high sensitivity to detect infectious virus.J Clin Virol. 2021; 140104846Crossref PubMed Scopus (29) Google Scholar, 2Corman VM Haage VC Bleicker T et al.Comparison of seven commercial SARS-CoV-2 rapid point-of-care antigen tests: a single-centre laboratory evaluation study.Lancet Microbe. 2021; (published online April 7.)https://doi.org/10.1016/S2666-5247(21)00056-2Summary Full Text Full Text PDF Scopus (171) Google Scholar However, the majority of Ag-RDT validation studies were done before SARS-CoV-2 variants of concern (VOC) or interest (VOI) emerged, with the VOCs currently outcompeting earlier lineages.3WHOWeekly epidemiological update on COVID-19.https://www.who.int/publications/m/item/weekly-epidemiological-update-on-covid-19---11-may-2021Date: May, 11 2021Date accessed: May 17, 2021Google Scholar To date, data on routine diagnostic performance for VOCs and VOIs are sparse.4Jungnick S Hobmaier B Mautner L et al.Detection of the new SARS-CoV-2 variants of concern B.1.1.7 and B.1.351 in five SARS-CoV-2 rapid antigen tests (RATs), Germany, March 2021.Euro Surveill. 2021; 262100413Crossref Scopus (38) Google Scholar, 5Public Health EnglandGuidance SARS-CoV-2 lateral flow antigen tests: evaluation of VUI-202012/01.https://www.gov.uk/government/publications/sars-cov-2-lateral-flow-antigen-tests-evaluation-of-vui-20201201/sars-cov-2-lateral-flow-antigen-tests-evaluation-of-vui-20201201Date: Dec 23, 2020Date accessed: May 17, 2021Google Scholar Furthermore, clinical validation studies comparing multiple VOCs in parallel are hardly feasible. We investigated the analytical sensitivity of nine commercially available Ag-RDTs using cultured SARS-CoV-2, comparing lineage B.1.610 (first COVID-19 pandemic wave in Europe) with VOCs B.1.1.7, B.1.351, and P.1, and VOI P.2. Infectious titres and RNA copies of virus stocks grown in Vero E6 were quantified by plaque titration (for infectious titres) and RT-PCR (E gene). Isolates were tested in serial dilutions, starting with 5·44 log10 PFU/mL, except for P.1, which had a maximum titre of log10 4·24 PFU/mL. An infectious titre of 5·44 log10 PFU/mL corresponded to 10.26, 12.11, 9.86, and 11·23 log10 RNA copies per mL for B.1.610, B.1.1.7, B.1.351 and P.2. For P.1, the infectious titre of 4·24 log10 PFU/mL corresponded to 11·81 log10 RNA copies per mL. Ag-RDT assays were done according to the manufacturers' instructions, with the exception that 5 μL of virus dilution was directly added to the proprietary buffer, and then applied to the Ag-RDT in duplicates under BSL3 conditions. Results were read independently by two individuals. Any visible test band in the presence of a visible control band was considered as positive. Ag-RDT buffer without virus was used as negative control. When analysing results normalised to PFU/mL, comparable or better performance to the early-pandemic lineage was observed for B.1.1.7, B.1.351, P.1, and P.2 for all assays (appendix). Overall sensitivity and specificity for individual isolates varied between Ag-RDTs, with the best-performing assay positive at dilutions as low as 2·43 log10 PFU/mL and the lower-sensitive assays positive at 4·54 log10 PFU/mL. Consistently, the highest sensitivity was seen for P.1 and P.2. Although testing for analytical sensitivity with cultured virus cannot fully replace clinical data, our data provide reassuring results for the use of Ag-RDTs to diagnose VOCs. Phenotypic properties, such as a large difference in the RNA–infectious virus ratio, could hint at production of defective viral particles and their effect on diagnostic test performance should be further investigated. This work was supported by the Swiss National Science Foundation (grant number 196383), the Fondation Ancrage Bienfaisance du Groupe Pictet, and the Foundation for Innovative New Diagnostics (FIND). The Swiss National Science Foundation and the Fondation Ancrage Bienfaisance du Groupe Pictet had no role in data collection, analysis, or interpretation. Antigen-detecting rapid diagnostic tests were provided by FIND and FIND was involved in methodology, data analysis, interpretation and writing. JAE and CE are employees of FIND. We declare no competing interests. Download .pdf (.17 MB) Help with pdf files Supplementary appendix SARS-CoV-2 antigen-detecting rapid tests for the delta variantGiven the emergence of novel SARS-CoV-2 variants of concern, the performance of available diagnostics for these new variants should be investigated. SARS-CoV-2 antigen rapid diagnostic tests (Ag-RDTs) offer quick, cheap, and laboratory-independent results at the point of care.1,2 Although sensitivity is lower compared with RT-PCR, these tests enable reliable detection of high viral loads associated with the presence of infectious viral particles, making them important public health tools.3,4 However, the majority of Ag-RDT validation studies were done before the emergence of SARS-CoV-2 variants of concern. Full-Text PDF Open Access

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