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
specificity of 57.6 and 99.5%, respectively with an accuracy of 82.6%. The cut-off
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 15min at the peak of the
pandemic. Its role in the proposed diagnostic algorithm is complementary to the
currently-used molecular techniques