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 ready-to-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 analyzed for the crossreactivity study. The clinical performance study was performed in a retrospective multicentric 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 cross-reactivity with other virus-infected nasopharyngeal samples. In the clinical performance study performed in three different clinical laboratories during the ascendant phase of the epidemiological curve, we found an overall sensitivity and Mertens et al. Respi-Strip Assay for Diagnosing COVID-19 specificity of 57.6 and 99.5%, respectively with an accuracy of 82.6%. The cutoff of the ICT 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 min at the peak of the pandemic. Its role in the proposed diagnostic algorithm is complementary to the currently-used molecular techniques.

Head-to-head comparison of four antigen-based rapid detection tests for the diagnosis of SARS-CoV-2 in respiratory samples

“…Another assay with visual bands (Respi-Strip CORIS) was recently evaluated in two European studies. Overall sensitivity ranged from 50% to 57.6%; however, detection rates improved for samples with high viral loads (Ct <25) reaching sensitivities of 73.9% to 82.2% (16, 17). The other two assays evaluated by us showed an insufficient performance.…”

“…Demographic and clinical data were obtained from the mandatory Covid-19 notification forms and analyzed in an anonymized manner. Samples with high viral loads (defined as Ct value <25) were compared to those with low viral load (Ct values >25) (16). Statistical analyses were performed with OpenEpi (version 3.01) and GraphPad Prism (version 8.4.2).…”

Laboratory testing for the diagnosis of COVID-19

“…Users of these antigen tests should be aware that the sensitivity varies significantly with different assays. The average sensitivity was 56% with a range from 0% to 95% [ [48] , [49] , [50] , [51] ], False positive occurs infrequently. The specificity are reported to be high (>97%) [ 47 ] and are most commonly due to cross-reaction with proteins in other human coronaviruses.…”

Biomedical Science to Tackle the COVID-19 Pandemic: Current Status and Future Perspectives

“…Interestingly, the sensitivity values of these assays were significantly higher than the ones obtained via qRT-PCR. On the other hand, Mertens et al developed the COVID-19 Au Respi-Strip© consisting of a nitrocellulose membrane onto which were cast AuNPs bioconjugated with monoclonal antibodies against SARS-CoV-2 [ 201 ]. Once this strip is immersed in a sample-containing test tube, the response is obtained within 15 min with a 74.2% sensitivity, a 100.0% specificity, and a 98.0% robustness, as illustrated in Figure 6 .…”

“… Working principle of SARS-COV-2 Respi-Strip©. Reproduced from Reference [ 201 ], under the Creative Commons Attribution License. …”