Rapid Evaluation of the Xpert® Xpress CoV-2 plus and Xpert® Xpress CoV-2/Flu/RSV plus Tests

Lara Dominique Noble; Lesley Erica Scott; Riffat Munir; Mignon Du Plessis; Kim Steegen; Lucia Hans; Puleng Marokane; Pedro Da Silva; Wendy Susan Stevens

doi:10.3390/diagnostics13010034

Rapid Evaluation of the Xpert^® Xpress CoV-2 plus and Xpert^® Xpress CoV-2/Flu/RSV plus Tests

Diagnostics (Basel). 2022 Dec 22;13(1):34. doi: 10.3390/diagnostics13010034.

Authors

Lara Dominique Noble¹, Lesley Erica Scott¹, Riffat Munir¹, Mignon Du Plessis^{2

3}, Kim Steegen^{3

4}, Lucia Hans^{3

4}, Puleng Marokane⁴, Pedro Da Silva⁴, Wendy Susan Stevens^{1

4}

Affiliations

¹ WITS Diagnostic Innovation Hub, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa.
² Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Division of the National Health Laboratory Service, Johannesburg 2192, South Africa.
³ School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 2000, South Africa.
⁴ National Priority Programmes, National Health Laboratory Service, Johannesburg 2000, South Africa.

Abstract

The Xpert^® Xpress SARS-CoV-2 and Xpert^® Xpress SARS-CoV-2/Flu/RSV tests were rapidly developed and widely used during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. In response to emerging genetic variability, a new SARS-CoV-2 target (RNA-dependent RNA-polymerase) has been added to both tests: Xpert^® Xpress CoV-2 plus and Xpert^® Xpress CoV-2/Flu/RSV plus test. A rapid evaluation of both tests was performed in South Africa, using residual respiratory specimens. Residual respiratory specimens (n = 125) were used to evaluate the Xpert^® Xpress CoV-2 plus test and included 50 genotyped specimens. The Xpert^® Xpress CoV-2/Flu/RSV plus test was assessed using 45 genotyped SARS-CoV-2 specimens, 10 influenza A, 10 influenza B and 20 respiratory syncytial virus specimens. Results were compared to in-country standard-of-care tests. Genotyped specimens tested the performance of the test under pressure from circulating SARS-CoV-2 variants of concern. Reference material was included to assess the test limits and linearity. The Xpert^® Xpress CoV-2 plus test performance compared to reference results across residual respiratory specimens was good (positive percentage agreement (PPA) = 95.2%, negative percentage agreement (NPA) = 95.0%) The Xpert^® Xpress CoV-2/Flu/RSV plus test showed good performance across all residual respiratory specimens (PPA = 100%, NPA = 98.3%). All genotyped variants of concern were detected by both tests. The Xpert^® Xpress CoV-2 plus and Xpert^® Xpress CoV-2/Flu/RSV plus tests can be used to diagnose SARS-CoV-2, and to diagnose and differentiate SARS-CoV-2, influenza A, influenza B and respiratory syncytial virus, respectively. The NPA was lower than the recommended 99%, but was influenced by the low number of negative specimens tested. The variants of concern assessed did not affect test performance. It is recommended that sites perform their own assessments compared to in-country standard-of-care tests.

Keywords: SARS-CoV-2; Xpert®; Xpert® Xpress CoV-2 plus; Xpress CoV-2/Flu/RSV plus; diagnostic evaluation; novel target; respiratory tests.

Grants and funding

INV-006726/GATES/Bill & Melinda Gates Foundation/United States