Evaluation of two fluorescence immunoassays for the rapid detection of SARS-CoV-2 antigen—new tool to detect infective COVID-19 patients

  1. Lorena Porte
  2. Paulette Legarraga
  3. Mirentxu Iruretagoyena
  4. Valeska Vollrath
  5. Gabriel Pizarro
  6. Jose Munita
  7. Rafael Araos
  8. Thomas Weitzel

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Abstract

Real-Time Reverse-Transcription Polymerase Chain Reaction (RT-PCR) is currently the only recommended diagnostic method for SARS-CoV-2. However, rapid immunoassays for SARS-CoV-2 antigen could significantly reduce the COVID-19 burden currently weighing on laboratories around the world.

Methods

We evaluated the performance of two rapid fluorescence immunoassays (FIAs), SOFIA SARS Antigen FIA (Quidel Corporation, San Diego, CA, USA) and STANDARD F COVID-19 Ag FIA (SD Biosensor Inc., Gyeonggi-do, Republic of Korea), which use an automated reader. The study used 64 RT-PCR characterized clinical samples (32 positive; 32 negative), which consisted of nasopharyngeal swabs in universal transport medium.

Results

Of the 32 positive specimens, all from patients within 5 days of symptom onset, the Quidel and SD Biosensor assays detected 30 (93.8%) and 29 (90.6%) samples, respectively. Among the 27 samples with high viral loads (Ct ≤ 25), the two tests had a sensitivity of 100%. Specificity was 96.9% for both kits.

Conclusion

The high performance of the evaluated FIAs indicates a potential use as rapid and PCR-independent tools for COVID-19 diagnosis in early stages of infection. The excellent sensitivity to detect cases with viral loads above ~10 6 copies/mL (Ct values ≤ 25), the estimated threshold of contagiousness, suggests that the assays might serve to rapidly identify infective individuals.

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  1. ScreenIT

    SciScore for 10.1101/2020.10.04.20206466: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board StatementIRB: The study was approved by the institutional review board (
    Consent: (Comité Etico Científico, Facultad de Medicina Clínica Alemana, Universidad del Desarrollo, Santiago, Chile) and a waiver of informed consent was granted.
    Randomizationnot detected.
    BlindingAssays were performed using the same sample aliquot, following manufacturers’ instructions, by the same laboratory personnel, who were blinded to RT-PCR results.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.
    Cell Line AuthenticationAuthentication: Both tests detect SARS-CoV-2 nucleocapsid protein by lateral flow immunofluorescence, which is interpreted by automated analysers (SOFIA 2, Quidel Corporation; F2400, SD Biosensor Inc.).

    Table 2: Resources

    No key resources detected.

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    However, material shortages and laboratory capacity limitations, especially during high transmission situations, have caused significant problems and led to the emergence of various new PCR-independent diagnostics [10]. Antigen-based assays are among the most recent developments, but peer-reviewed evaluations of their diagnostic performance are scarce. Hence, their role within the routine diagnostic workup is yet not defined [9,11]. Since antigen detection per se has a lower sensitivity than RT-PCR, it will most likely not replace it [9]. However, the results of this and former studies indicate that antigen detection by immunofluorescence, especially when used with an automated reader, has an excellent sensitivity to detect SARS-CoV-2 in samples with estimated viral loads above ∼106 copies/mL (Ct values ≤25) [9], which are found in pre-symptomatic (1-3 days before symptom onset) and early symptomatic Covid-19 cases (5-7 days after symptom onset) [9,12-14]. According to recent modelling studies, elevated viral titers are associated to infectivity [15]. This is in accordance with in vitro experiments, which showed no viral growth from samples with Cts >24 or taken >8 days after symptom onset [16,17]. A viral load of 106 copies/mL has therefore been suggested as the limit of infectivity for clinical practice [18]. However, until the exact threshold of contagiousness is known, other authors have considered a more conservative approach (1,000 copies/mL) [19]. For samples with high...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

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  2. Version published to 10.7717/peerj.10801
  3. Version published to 10.1101/2020.10.04.20206466v1 on medRxiv