[Microbiologia Medica 2021; 36:9623] [page 21] Summary Background and aims: Rapid and accurate diagnosis is essen- tial to limit the spread of SARS-CoV-2 and for patient’s manage- ment. Currently, real-time reverse transcription polymerase chain reaction (RT-PCR) is the recommended laboratory test to detect SARS-CoV-2. However, the requirement of special instruments and skilled personnel have limited the use of this technique. Recently, several rapid antigen detection tests have been devel- oped and used as frontline. The aim of this work was to assess the performances of STANDARD F COVID-19 Ag FIA Kit, a rapid fluorescence immunoassay for the detection of SARS-CoV-2 nucleoprotein antigens, in comparison to RT-PCR. Materials and methods: Twenty-three nasopharyngeal swabs were collected and tested. Results: Among the 20 positive RT-PCR samples, 9 were detected by the immunofluorescence assay, reporting an overall sensitivity of 45%. The sensitivity increased to 64% in the case of a high viral load, where all three target genes, RdRp, N, and E, were detected by RT-PCR. Conclusions: A better antigen detection rate is associated with low Cycle threshold values which are inversely related to the viral load. STANDARD F COVID-19 Ag test cannot be considered as the frontline assay for COVID-19 diagnosis, but it might be used in association with clinical signs of patients to reduce the number of RT-PCR testing. Introduction The three epidemic outbreaks caused by human coronavirus (hCoV), i.e. SARS-CoV, MERS-CoV and SARS-CoV-2, emerging at the beginning of the 21 st century, have highlighted the need for fast and accurate diagnostic assays. Initially reported in China, the last human coronavirus disease (COVID-19) caused by SARS- CoV-2 has spread rapidly around the world and it has become a major public health (1,2). Early diagnosis is crucial for the detection of COVID-19 infected subjects in order to control and limit the out- break (3). The current gold-standard assay for the detection of SARS-CoV-2 is based on viral RNA amplification by using reverse transcription PCR (RT-PCR) (4). This test requires an average exe- cution time of 2/3 hours, except for GeneXpert system (Cepheid 904, USA) which can provide a result in 50 minutes, but it needs skilled personnel and it is expensive. Therefore, the evaluation of immunological diagnostic assays which can detect SARS-CoV-2 antigens at lower costs compared to molecular tests, might be help- ful for a rapid and accurate diagnosis of COVID-19. Currently, there are different immunological tests that can detect SARS-CoV-2 nucleoprotein antigens. These assays are performed by using differ- ent methodologies, as enzyme-linked immunosorbent assay (ELISA), chemiluminescence immunoassay (CLIA), colloidal gold immunochromatography and fluorescent immunoassays (FIA) (3,5,6). The aim of this study was to assess the performances of commercial STANDARD F COVID-19 Ag FIA Kit in comparison to molecular test for laboratory detection of SARS-CoV-2. Correspondence: Carcione Davide, Department of Laboratory Medicine, Centro Cardiologico Monzino IRCCS, Milan; Department of Laboratory Medicine, University of Milano-Bicocca, Azienda Socio Sanitaria Territoriale della Brianza ASST-Brianza, Desio Hospital, Desio (MB), Italy. Tel.: +39.0362383400. E-mail: davide.carcione@asst-brianza.it Key words: Antigen; SARS-CoV-2; COVID-19; Rapid antigen detec- tion test. Acknowledgments: the authors gratefully acknowledge Dr. Elena Intra for reviewing the manuscript. Contributions: DC and JI wrote the manuscript; DC designed the study; DR, SS, and LR performed the sample analysis; SB performed the sta- tistical analysis; VL and MLB critically revised the manuscript. All authors have accepted responsibility for the entire content of the sub- mitted manuscript and approved submission. Conflict of interest: the authors declare no potential conflict of interest. Funding: None. Received for publication: 18 January 2021. Revision received: 10 March 2021. Accepted for publication: 23 March 2021. © Copyright: the Author(s), 2021 Licensee PAGEPress, Italy Microbiologia Medica 2021; 36:9623 doi:10.4081/mm.2021.9623 This article is distributed under the terms of the Creative Commons Attribution Noncommercial License (by-nc 4.0) which permits any non- commercial use, distribution, and reproduction in any medium, provid- ed the original author(s) and source are credited. Journal of Entomological and Acarological Research 2012; volume 44:e Microbiologia Medica 2021; volume 36:9623 Evaluation of a rapid diagnostic test for detection of SARS-CoV-2 antigen in nasopharyngeal swabs Davide Carcione, 1,2 Jari Intra, 2 Daniela Riggio, 1 Simona Sabella, 1 Lorenza Rondelli, 1 Simone Barbieri, 3 Valerio Leoni, 3 Maria Luisa Biondi 1 1 Department of Laboratory Medicine, Centro Cardiologico Monzino IRCCS, Milan; 2 Department of Laboratory Medicine, University of Milano-Bicocca, Azienda Socio Sanitaria Territoriale della Brianza ASST-Brianza, Desio Hospital, Desio (MB); 3 Biostatistic Unit, Centro Cardiologico Monzino IRCCS, Milan, Italy Non-commercial use only