Development and potential usefulness of the COVID-19 Ag Respi-Strip® diagnostic assay in a pandemic context

Abstract

Introduction: COVID-19 Ag Respi-Strip, an immunochromatographic (ICT) assay for the rapid detection of SARS-CoV-2 antigen on nasopharyngeal specimen, has been developed to identify positive COVID-19 patients allowing prompt clinical and quarantine decisions. In this Original Research article, we describe the conception, the analytical and clinical performances as well as the risk management of implementing the COVID-19 Ag Respi-Strip in a diagnostic decision algorithm. Materials and Methods: Development of the COVID-19 Ag Respi-Strip resulted in a readyto-use ICT assay based on a membrane technology with colloidal gold nanoparticles using monoclonal antibodies directed against the SARS-CoV and SARS-CoV-2 highly conserved nucleoprotein antigen. Four hundred observations were recorded for the analytical performance study and thirty tests were analysed for the cross-reactivity study. The clinical performance study was performed in a retrospective multi-centric evaluation on aliquots of 328 nasopharyngeal samples. COVID-19 Ag Respi-Strip results were compared with qRT-PCR as golden standard for COVID-19 diagnostics.Results: In the analytical performance study, the reproducibility showed a between-observer disagreement of 1.7%, a robustness of 98%, an overall satisfying user friendliness and no crossreactivity with other virus-infected nasopharyngeal samples. In the clinical performance study performed in three different clinical laboratories we found an overall sensitivity and specificity of 57.6% and 99.5% respectively with an accuracy of 82.6%. The cut-off of the assay was found at Ct<22. User-friendliness analysis and risk management assessment through Ishikawa diagram demonstrate that COVID-19 Ag Respi-Strip may be implemented in clinical laboratories according to biosafety recommendations. Conclusion:The COVID-19 Ag Respi-Strip represents a promising rapid SARS-CoV-2 antigen assay for the first-line diagnosis of COVID-19 in 15 minutes. Its role in the proposed diagnostic algorithm is complementary to the currently-used molecular techniques.

Implementation of rapid SARS-CoV-2 antigenic testing in a laboratory without access to molecular methods: Experiences of a general hospital

“…Under routine conditions, the sensitivity of the antigen detection of SARS-CoV-2 with the immunochromatographic COVID-19 Ag Respi-Strip kit was significantly lower than that announced by the manufacturer or reported by Vandenberg [2], although we limited ourselves to using qRT-PCR as the comparison method. In our series, we observed a median sensitivity of 23.9 %.…”

“…The WHO estimates that at least half of COVID-19-infected patients might be missed by such tests and therefore does not currently recommend their use. Vandenberg calculated their performance based on a threshold cycle (Ct) below 22 [2]. In the meantime, a notice from the manufacturer signalled that some hospitals observed negative results with a Ct of 13.45 or positive results with a Ct higher than 33, underlining the unclear relationship between protein and RNA detection.…”

“…We read with great interest the early April WHO advice on the use of point-of-care immunodiagnostic tests for COVID-19 [1] as well as the article recently published on the test validation [2] and wanted to evaluate our current way of working.…”