Lateral flow antigen tests can sensitively detect live cultured virus of the SARS-CoV-2 B1.1.7 lineage

Kontogianni, Konstantina, Cubas-Atienzar, Ana, Wooding, Dominic, Buist, Kate, Thompson, Caitlin, Williams, Chris, Baldwin, Lisa, Escadafal, Camille, Sacks, Jilian A., Adams, Emily ORCID: https://orcid.org/0000-0002-0816-2835 and Edwards, Thomas (2021) 'Lateral flow antigen tests can sensitively detect live cultured virus of the SARS-CoV-2 B1.1.7 lineage'. Journal of Infection, Vol 83, Issue 1, e1-e4.

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Abstract

We read with interest recent evaluations of SARS-CoV-2 antigen rapid diagnostic tests (Ag-RDTs), showing high sensitivity for detecting cases with higher viral loads.1 The clinical sensitivity of these tests relies on their limit of detection (LOD), and there are concerns that new SARS-CoV-2 variants may affect test performance.
New variants of SARS-CoV-2 have arisen worldwide, including the lineage B.1.1.7 (Variant of Concern (VOC) strain 202,012/01), which has become the dominant circulating SARS-CoV-2 strain in the U.K., causing >95% of new infections as of April 2021.2 Lineage B.1.1.7 has now been detected in over 114 countries in Europe, America, Australia, Asia and Africa. B.1.1.7 has 17 mutations compared with the original circulating virus, including 8 in the spike protein (S), and 2 in the nucleoprotein (N).3 Most Ag-RDTs target N protein with some targeting the S protein. Therefore, these mutations may affect antibody binding in the Ag-RDT, and consequently affect the assay sensitivity. The impact of these mutations on molecular diagnostics has been demonstrated by the failure of S gene detection probes in some nucleic acid tests.4
It is essential that Ag-RDTs are re-evaluated using new variants to determine if there is any change in test sensitivity due to mutations in the target antigen. The aim of this study was to determine the LOD of seventeen commercially available RDTs using the B.1.1.7 lineage and compare results obtained with the original dominant strain (B.1).
A clinically isolated SARS-CoV-2 strain from the B.1.1.7 lineage (Genbank accession number: MW980115), was used for the study. Frozen aliquots of the third passage of the virus were quantified via plaque assay as previously described.5 For the determination of LODs, a fresh aliquot was serially diluted from 1.0 × 106 plaque forming units (pfu)/ml to 1.0 × 102 pfu/ml. Each dilution was tested in triplicate. Two-fold dilutions were made below the ten-fold LOD dilution to confirm the lowest LOD. Culture media was used as negative control.
Viral RNA was extracted from each dilution using QIAmp Viral RNA mini kit (Qiagen, Germany) according to the manufacturer's instructions, and quantified using TaqPath COVID-19 CE-IVD RT-PCR (ThermoFisher). Genome copy number/ml (gcn/ml) were calculated as previously described.6
We evaluated 17 commercially available Ag-RDT tests (Table 1) following the instructions for use (IFU). The LOD was defined as the lowest dilution at which all three replicates were positive. Results were interpreted by two operators, each blinded to the result of the other. If a discrepant result was obtained, a third operator read any discrepant tests as a tie-breaker.
Table 1Characteristics of the Ag-RDT tested.

Item Type:	Article
Subjects:	QW Microbiology and Immunology > Viruses > QW 160 Viruses (General). Virology QW Microbiology and Immunology > Antigens and Antibodies. Toxins and Antitoxins > QW 573 Antigens WC Communicable Diseases > Virus Diseases > Viral Respiratory Tract Infections. Respirovirus Infections > WC 505 Viral respiratory tract infections
Faculty: Department:	Biological Sciences > Department of Tropical Disease Biology
Digital Object Identifer (DOI):	https://doi.org/10.1016/j.jinf.2021.05.033
Depositing User:	Marie Hatton
Date Deposited:	14 Jun 2021 10:21
Last Modified:	29 May 2022 01:02
URI:	https://archive.lstmed.ac.uk/id/eprint/18076

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