Femtomolar SARS-CoV-2 Antigen Detection Using the Microbubbling Digital Assay with Smartphone Readout Enables Antigen Burden Quantitation and Tracking. (12th August 2021)

• Record Type: Journal Article
• Authors: Chen, Hui; Li, Zhao; Feng, Sheng; Richard-Greenblatt, Melissa; Hutson, Emily; Andrianus, Stefen; Glaser, Laurel J; Rodino, Kyle G; Qian, Jianing; Jayaraman, Dinesh; Collman, Ronald G; Glascock, Abigail; Bushman, Frederic D; Lee, Jae Seung; Cherry, Sara; Fausto, Alejandra; Weiss, Susan R; Koo, Hyun; Corby, Patricia M; Oceguera, Alfonso; O'Doherty, Una; Garfall, Alfred L; Vogl, Dan T; Stadtmauer, Edward A; Wang, Ping
• Is Part Of: Clinical chemistry. Volume 68:Number 1(2022)
• Page Start: 230
• Page End: 239
• Publication Date: 2021-08-12
• Subjects: SARS-CoV-2 -- viral antigen -- longitudinal NP swab samples -- microbubbling assay; Clinical chemistry -- Periodicals; Pharmaceutical chemistry -- Periodicals; Biochemistry -- Periodicals; Biochimie -- Périodiques; Diagnostics biologiques -- Périodiques; Biochemistry; Clinical chemistry; Pharmaceutical chemistry; Biochemistry; Laboratory Techniques and Procedures; Klinische chemie; Periodicals; 616.075605
• DOI: 10.1093/clinchem/hvab158
• Languages: English
• ISSNs: 0009-9147

Abstract

Abstract: Background: High-sensitivity severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen assays are desirable to mitigate false negative results. Limited data are available to quantify and track SARS-CoV-2 antigen burden in respiratory samples from different populations. Methods: We developed the Microbubbling SARS-CoV-2 Antigen Assay (MSAA) with smartphone readout, with a limit of detection of 0.5 pg/mL (10.6 fmol/L) nucleocapsid antigen or 4000 copies/mL inactivated SARS-CoV-2 virus in nasopharyngeal (NP) swabs. We developed a computer vision and machine learning–based automatic microbubble image classifier to accurately identify positives and negatives and quantified and tracked antigen dynamics in intensive care unit coronavirus disease 2019 (COVID-19) inpatients and immunocompromised COVID-19 patients. Results: Compared to qualitative reverse transcription−polymerase chain reaction methods, the MSAA demonstrated a positive percentage agreement of 97% (95% CI 92%–99%) and a negative percentage agreement of 97% (95% CI 94%–100%) in a clinical validation study with 372 residual clinical NP swabs. In immunocompetent individuals, the antigen positivity rate in swabs decreased as days-after-symptom-onset increased, despite persistent nucleic acid positivity. Antigen was detected for longer and variable periods of time in immunocompromised patients with hematologic malignancies. Total microbubble volume, a quantitative marker of antigen burden, correlated inversely with cycle threshold values and days-after-symptom-onset. Viral sequence variations were detected in patients with long duration of high antigen burden. Conclusions: The MSAA enables sensitive and specific detection of acute infections and quantification and tracking of antigen burden and may serve as a screening method in longitudinal studies to identify patients who are likely experiencing active rounds of ongoing replication and warrant close viral sequence monitoring.