SARS-CoV-2 serology in 4000 health care and administrative staff across seven sites in Lombardy, Italy

  1. Maria Teresa Sandri
  2. Elena Azzolini
  3. Valter Torri
  4. Sara Carloni
  5. Chiara Pozzi
  6. Michela Salvatici
  7. Michele Tedeschi
  8. Massimo Castoldi
  9. Alberto Mantovani
  10. Maria Rescigno

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Abstract

Lombardy is the Italian region most affected by COVID-19. We tested the presence of plasma anti-SARS-CoV-2 IgG antibodies in 3985 employees across 7 healthcare facilities in areas of Lombardy with different exposure to the SARS-CoV-2 epidemic. Subjects filled a questionnaire to self-report on COVID-19 symptoms, comorbidities, smoking, regular or remote working, and the exposure to COVID-infected individuals. We show that the number of individuals exposed to the virus depended on the geographical location of the facility, ranging between 3 and 43%, consistent with the spatial variation of COVID-19 incidence in Lombardy, and correlated with family interactions. We observed a higher prevalence of females than males positive for IgG, however the level of antibodies was similar, suggesting a comparable magnitude of the anti-spike antibody response. IgG positivity among smokers was lower (7.4% vs 13.5%) although without difference in IgG plasma levels. We observed 11.9% of IgG positive asymptomatic individuals and another 23.1% with one or two symptoms. Interestingly, among the IgG positive population, 81.2% of subjects with anosmia/dysgeusia and fever were SARS-CoV-2 infected, indicating that these symptoms are strongly associated to COVID-19. In conclusion, the frequency of IgG positivity and SARS-CoV-2 infection is dependent on the geographical exposure to the virus and primarily to family rather than hospital exposure.

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  1. Version published to 10.1038/s41598-021-91773-4
  2. Version published to 10.1101/2020.05.24.20111245v2 on medRxiv
  3. ScreenIT

    SciScore for 10.1101/2020.05.24.20111245: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementIRB: Clinical Study: The study has been approved by the international review board of Istituto Clinico Humanitas for all participating institutes (clinicaltrial.gov NCT04387929).
    Consent: All participants signed an informed consent and filled a questionnaire (Supplementary Data S1) before blood collection.
    Randomizationnot detected.
    Blindingnot detected.
    Power AnalysisNo power analysis was performed to calculate the sample size.
    Sex as a biological variablenot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    The method is an indirect chemiluminescence immunoassay for the determination of anti-S1 and anti-S2 specific antibodies.
    anti-S1
    suggested: None
    anti-S2
    suggested: None
    Statistics: This was a cross sectional study aimed at determining the frequency of plasma anti-SARS-CoV-2 IgG antibodies in nearly 4000 (3985) employees of 7 different healthcare facilities located in Lombardy.
    anti-SARS-CoV-2 IgG
    suggested: None
    Software and Algorithms
    SentencesResources
    RNA extraction was performed using Seegene Nimbus, a liquid handler workstation, Real-time PCR was run on a CFX96 TMDx thermocycler (Bio-Rad Laboratories, Inc, CA, USA) and subsequently interpreted by Seegene’s Viewer software.
    Bio-Rad Laboratories
    suggested: (Bio-Rad Laboratories, RRID:SCR_008426)
    Kruskal–Wallis and non-parametric tests for trend (Cuzick’s and Mantel-Haenzel test, when appropriate) have been used for multiple comparisons using Prism 8 Graphpad.
    Graphpad
    suggested: (GraphPad, RRID:SCR_000306)

    Results from OddPub: Thank you for sharing your data.

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    In conclusion, our study has some limitations, as it is monitoring healthcare workers, and thus it does not reflect a comprehensive population as a good proportion of professionals are women and there is an underrepresentation of the elderly due to working age limit. However, we show that antibody testing can identify the individuals that were exposed to SARS-CoV-2 and is a powerful tool to retrospectively evaluate viral diffusion, even in asymptomatic individuals. Another limitation of the study is that we may have missed the population of subjects which do not develop an antibody response or that is reduced over time. As our study is ongoing we will assess the evolution of the IgG response over a planned follow up of one year, allowing for measuring the duration of the antibody response. Should a second wave of SARS-CoV-2 infection occur, the wide range of IgG serology in the different sites will be particularly valuable as it will allow us to assess the role of antibodies in viral protection. As we also collected the PBMC from a good proportion of our cohort, this will allow us to evaluate whether the T cell response lasts longer than the B cell response and may highlight individuals exposed to the virus which have not seroconverted, or whose level of antibodies was below 12 AU/mL. The results presented here suggest that hospital health care professionals, researchers and administrative staff can provide invaluable information to assess variables affecting the immune respo...

    Results from TrialIdentifier: We found the following clinical trial numbers in your paper:

    IdentifierStatusTitle
    NCT04387929RecruitingDetection of Anti-COVID-19 Antibody Levels in an Hospital Po…

    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

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  4. Version published to 10.1101/2020.05.24.20111245v1 on medRxiv