On-field evaluation of a ultra-rapid fluorescence immunoassay as a frontline test for SARS-CoV-2 diagnostic

BACKGROUND: Viral RNA amplification by real-time RT-PCR still represents the gold standard for the detection of SARS-CoV-2, but the development of rapid, reliable and easy-to-perform diagnostic methods is crucial for public health, because of the need of shortening the time of result-reporting with a cost-efficient approach. OBJECTIVES: The aim of our research was to assess the performance of FREND™ COVID-19 Ag assay (NanoEntek, South Korea) as a ultra-rapid frontline test for SARS-CoV-2 identification, in comparison with RT-PCR and another COVID-19 antigen fluorescence immunoassay (FIA). STUDY DESIGN: The qualitative FIA FREND™ test, designed to detect within 3 min the Nucleocapsid protein of SARS-CoV-2, was evaluated using nasopharyngeal swabs in Universal Transport Medium (UTM™, Copan Diagnostics Inc, US) from suspected COVID-19 cases who accessed the Emergency Room of the Ospedale Policlinico San Martino, Genoa, Liguria, Northwest Italy. Diagnostic accuracy was determined in comparison with SARS-CoV-2 RT-PCR and STANDARD F™ COVID-19 Ag FIA test (SD BIOSENSOR Inc., Republic of Korea). RESULTS: In November 2020, 110 nasopharyngeal samples were collected consecutively; 60 resulted RT-PCR positive. With respect to RT-PCR results, sensitivity and specificity of FREND™ COVID-19 Ag test were 93.3 % (95 % CI: 83.8−98.2) and 100 % (95 % CI: 92.9−100), respectively. FREND™and STANDARD F™ COVID-19 Ag FIA assays showed a concordance of 96.4 % (Cohen’s k = 0.93, 95 % CI: 0.86−0.99). CONCLUSIONS: FREND™ FIA test showed high sensitivity and specificity in nasopharyngeal swabs. The assay has the potential to become an important tool for an ultra-rapid identification of SARS-CoV-2 infection, particularly in situations with limited access to molecular diagnostics.