A Generic, Scalable, and Rapid Time-Resolved Förster Resonance Energy Transfer-Based Assay for Antigen Detection-SARS-CoV-2 as a Proof of Concept.

The ongoing coronavirus disease 2019 (COVID-19) pandemic has seen an unprecedented increase in the demand for rapid and reliable diagnostic tools, leaving many laboratories scrambling for resources. We present a fast and simple assay principle for antigen detection and demonstrate its functionality by detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in nasopharyngeal swabs. The method is based on the detection of SARS-CoV-2 nucleoprotein (NP) and S protein (SP) via time-resolved Förster resonance energy transfer (TR-FRET) with donor- and acceptor-labeled polyclonal anti-NP and -SP antibodies. Using recombinant proteins and cell culture-grown SARS-CoV-2, the limits of detection were established as 25 pg of NP or 20 infectious units (IU) and 875 pg of SP or 625 IU. Testing reverse transcription-PCR (RT-PCR)-positive (n = 48, with cycle threshold [CT ] values from 11 to 30) or -negative (n = 96) nasopharyngeal swabs demonstrated that the assay yielded positive results for all samples with CT values of <25 and for a single RT-PCR-negative sample. Virus isolation from the RT-PCR-positive nasopharyngeal swabs showed a strong association between the presence of infectious virus and a positive antigen test result. The NP-based assay showed 97.4% (37/38) sensitivity and 100% (10/10) specificity in comparison with virus isolation and 77.1% (37/48) sensitivity and 99.0% (95/96) specificity in comparison with SARS-CoV-2 RT-PCR. The assay is performed in a buffer that neutralizes SARS-CoV-2 infectivity, and the assay is relatively simple to set up as an "in-house" test. Here, SARS-CoV-2 served as the model pathogen, but the assay principle is applicable to other viral infections, and the test format could easily be adapted to high-throughput testing.IMPORTANCE PCR is currently the gold standard for the diagnosis of many acute infections. While PCR and its variants are highly sensitive and specific, the time from sampling to results is measured in hours at best. Antigen tests directly detect parts of the infectious agent, which may enable faster diagnosis but often at lower sensitivity and specificity. Here, we describe a technique for rapid antigen detection and demonstrate the test format's potential using SARS-CoV-2 as the model pathogen. The 10-min test, performed in a buffer that readily inactivates SARS-CoV-2, from nasopharyngeal samples identified 97.4% (37/38) of the samples from which we could isolate the virus. This suggests that the test performs well in identifying patients potentially shedding the virus. Although SARS-CoV-2 served as the model pathogen to demonstrate proof of concept, the test principle itself would be applicable to a wide variety of infectious and perhaps also noninfectious diseases.

Rusanen J ，Kareinen L ，Szirovicza L ，Uğurlu H ，Levanov L ，Jääskeläinen A ，Ahava M ，Kurkela S ，Saksela K ，Hedman K ，Vapalahti O ，Hepojoki J ... -  《mBio》

Sensitivity and Specificity of SARS-CoV-2 Rapid Antigen Detection Tests Using Oral, Anterior Nasal, and Nasopharyngeal Swabs: a Diagnostic Accuracy Study.

Wölfl-Duchek M ，Bergmann F ，Jorda A ，Weber M ，Müller M ，Seitz T ，Zoufaly A ，Strassl R ，Zeitlinger M ，Herkner H ，Schnidar H ，Anderle K ，Derhaschnig U ... -  《Microbiology Spectrum》

A 10-Minute "Mix and Read" Antibody Assay for SARS-CoV-2.

Rusanen J ，Kareinen L ，Levanov L ，Mero S ，Pakkanen SH ，Kantele A ，Amanat F ，Krammer F ，Hedman K ，Vapalahti O ，Hepojoki J ... -  《Viruses-Basel》

Accuracy of a nucleocapsid protein antigen rapid test in the diagnosis of SARS-CoV-2 infection.

Rapid, reliable and easy-to-implement diagnostics that can be adapted in early severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) diagnosis are critical to combat the epidemic. SARS-CoV-2 nucleocapsid protein (NP) is an ideal target for viral antigen-based detection. A rapid and convenient method was developed based on fluorescence immunochromatographic (FIC) assay to detect the SARS-CoV-2 NP antigen. However, the accuracy of this diagnostic method needs to be examined. This prospective study was carried out between 10 and 15 February 2020 in seven hospitals in Wuhan and one hospital in Chongqing, China. Participants with clinically suspected SARS-CoV-2 infection were enrolled. NP antigen testing by FIC assay and nucleic acid (NA) testing by real-time reverse transcriptase PCR (RT-PCR) were performed simultaneously in a blinded manner with the same nasopharyngeal swab sample. The diagnostic accuracy of NP antigen testing was calculated by taking NA testing of RT-PCR as the reference standard, in which samples with a cycle threshold (Ct) value of ≤40 were interpreted as positive for SARS-CoV-2. A total of 253 participants were enrolled; two participants were excluded from the analyses because of invalid NP testing results. Of 251 participants (99.2%) included in the diagnostic accuracy analysis, 201 (80.1%) had a Ct value of ≤40. With Ct value 40 as the cutoff of NA testing, the sensitivity, specificity and percentage agreement of the FIC assay was 75.6% (95% confidence interval, 69.0-81.3), 100% (95% confidence interval, 91.1-100) and 80.5% (95% confidence interval, 75.1-84.9) respectively. With RT-PCR assay as the reference standard, NP antigen testing by FIC assay shows high specificity and relatively high sensitivity in SARS-CoV-2 diagnosis in the early phase of infection.

Diao B ，Wen K ，Zhang J ，Chen J ，Han C ，Chen Y ，Wang S ，Deng G ，Zhou H ，Wu Y ... -  《-》

Quantifying SARS-CoV-2 nucleocapsid antigen in oropharyngeal swabs using single molecule array technology.

This study aimed to develop a highly sensitive SARS-CoV-2 nucleocapsid antigen assay using the single molecule array (Simoa) technology and compare it with real time RT-PCR as used in routine clinical practice with the ambition to achieve a comparative technical and clinical sensitivity. Samples were available from 148 SARS-CoV-2 real time RT-PCR positive and 73 SARS-CoV-2 real time RT-PCR negative oropharyngeal swabs. For determination of technical sensitivity SARS-CoV-2 virus culture material was used. The samples were treated with lysis buffer and analyzed using both an in-house and a pre-commercial SARS-CoV-2 nucleocapsid antigen assay on Simoa. Both nucleocapsid antigen assays have a technical sensitivity corresponding to around 100 SARS-CoV-2 RNA molecules/mL. Using a cut-off at 0.1 pg/mL the pre-commercial SARS-CoV-2 nucleocapsid antigen assay had a sensitivity of 96% (95% CI 91.4-98.5%) and specificity of 100% (95% CI 95.1-100%). In comparison the in-house nucleocapsid antigen assay had sensitivity of 95% (95% CI 89.3-98.1%) and a specificity of 100% (95% CI 95.1-100%) using a cut-off at 0.01 pg/mL. The two SARS-CoV-2 nucleocapsid antigen assays correlated with r = 0.91 (P < 0.0001). The in-house and the pre-commercial SARS-CoV-2 nucleocapsid antigen assay demonstrated technical and clinical sensitivity comparable to real-time RT-PCR methods for identifying SARS-CoV-2 infected patients and thus can be used clinically as well as serve as a reference method for antigen Point of Care Testing.

Olsen DA ，Brasen CL ，Kahns S ，Madsen JB ，Kierkegaard H ，Christensen H ，Jensen A ，Sydenham TV ，Møller JK ，Madsen JS ，Brandslund I ... -  《Scientific Reports》