Prevalence of SARS-CoV-2 antibodies among workers of the public higher education institutions of Porto, Portugal: a cross-sectional study

  1. Paula Meireles
  2. Joana Amaro
  3. Joana Pinto da Costa
  4. Mariana Mendes Lopes
  5. Tatiana Varandas
  6. Pedro Norton
  7. João Tiago Guimarães
  8. Milton Severo
  9. Henrique Barros

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Abstract

To assess the prevalence of SARS-CoV-2-specific IgM and IgG antibodies among workers of the three public higher education institutions of Porto, Portugal, up to July 2020.

Methods

A rapid point-of-care test for specific IgM and IgG antibodies of SARS-CoV-2 was offered to all workers (SD Biosensor STANDARD Q COVID-19 IgM/IgG Duo and STANDARD Q COVID-19 IgM/IgG Combo). Testing was performed and a questionnaire was completed by 4592 workers on a voluntary basis from 21 May to 31 July 2020. We computed the apparent IgM, IgG, and combined IgM or IgG prevalence, along with the true prevalence and 95% credible intervals (95% CrI) using Bayesian inference.

Results

We found an apparent prevalence of 3.1% for IgM, 1.0% for IgG and 3.9% for either. The estimated true prevalence was 2.0% (95% CrI 0.1% to 4.3%) for IgM, 0.6% (95% CrI 0.0% to 1.3%) for IgG, and 2.5% (95% CrI 0.1% to 5.3%) for IgM or IgG. A SARS-CoV-2 molecular diagnosis was reported by 21 (0.5%) workers; and of these, 90.5% had a reactive IgG result. Seroprevalence was higher among those reporting contacts with confirmed cases, having been quarantined, having a previous molecular negative test or having had symptoms.

Conclusions

The seroprevalence among workers from the three public higher education institutions of Porto after the first wave of the SARS-CoV-2 infection was similar to national estimates for the same age working population. However, the estimated true seroprevalence was approximately five times higher than the reported SARS-CoV-2 infection based on a molecular test.

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  1. Version published to 10.1136/oemed-2021-107519
  2. ScreenIT

    SciScore for 10.1101/2021.02.28.21252628: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementConsent: The self-administered questionnaire inquired about gender identity, nationality, educational level, occupation, currently working from home, self-perception of having been infected, travelling abroad since December 2019, contacts with confirmed SARS-CoV-2 cases and having been quarantined since January 2020 Participants provided written informed consent to all procedures.
    IRB: The study protocol was approved by the ethics committee of the Institute of Public Health of the University of Porto (ID 20154).
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    All workers of the three public higher education institutions of Porto were offered a serological point-of-care test for SARS-CoV-2 specific IgM and IgG antibodies, from May 21 to July 31, 2020.
    IgG
    suggested: None
    SARS-CoV-2 specific IgM and IgG antibodies determination and follow-up: Two point-of-care tests were used – the STANDARD Q COVID-19 IgM/IgG Duo used from May 21 to July 10, n=3987 (manufacturer reported sensitivity of 92.6% eight days after symptom onset and specificity of 96.5% for both IgG and IgM); and the STANDARD Q COVID-19 IgM/IgG Combo from July 10 to July 31, n=605 (manufacturer reported sensitivity of 94.5% seven or more days after symptom onset and specificity of 95.7% for both IgG and IgM).
    SARS-CoV-2 specific IgM
    suggested: None
    IgG antibodies determination
    suggested: (RevMAb Biosciences Cat# 31-1255-00, RRID:AB_2783608)
    IgM
    suggested: None

    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:
    These limitations do not seem to change the meaning of our main findings of a low seroprevalence of SARS-CoV-2 at the time of resuming working activities after the first wave of the SARS-CoV-2 infection; and that the estimated true seroprevalence was approximately five times greater than the reported SARS-CoV-2 infection burden using a molecular test information.

    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.

    About SciScore

    SciScore is an automated tool that is designed to assist expert reviewers by finding and presenting formulaic information scattered throughout a paper in a standard, easy to digest format. SciScore checks for the presence and correctness of RRIDs (research resource identifiers), and for rigor criteria such as sex and investigator blinding. For details on the theoretical underpinning of rigor criteria and the tools shown here, including references cited, please follow this link.

  3. Version published to 10.1101/2021.02.28.21252628v1 on medRxiv