Prevalence and incidence of anti-SARS-CoV-2 antibodies among healthcare workers in Belgian hospitals before vaccination: a prospective cohort study

  1. Laure Mortgat
  2. Kristien Verdonck
  3. Veronik Hutse
  4. Isabelle Thomas
  5. Cyril Barbezange
  6. Leo Heyndrickx
  7. Natalie Fischer
  8. Bea Vuylsteke
  9. Ines Kabouche
  10. Kevin K Ariën
  11. Isabelle Desombere
  12. Els Duysburgh

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Abstract

To describe prevalence and incidence of anti-SARS-CoV-2 antibodies among Belgian hospital healthcare workers (HCW) in April–December 2020.

Design

Prospective cohort study. Follow-up was originally planned until September and later extended.

Setting

Multicentre study, 17 hospitals.

Participants

50 HCW were randomly selected per hospital. HCW employed beyond the end of the study and whose profession involved contact with patients were eligible. 850 HCW entered the study in April–May 2020, 673 HCW (79%) attended the September visit and 308 (36%) the December visit.

Outcome measures

A semiquantitative ELISA was used to detect IgG against SARS-CoV-2 in serum (Euroimmun) at 10 time points. In seropositive samples, neutralising antibodies were measured using a virus neutralisation test. Real-time reverse transcription PCR (RT-qPCR) was performed to detect SARS-CoV-2 on nasopharyngeal swabs. Participant characteristics and the presence of symptoms were collected via an online questionnaire.

Results

Among all participants, 80% were women, 60% nurses and 21% physicians. Median age was 40 years. The seroprevalence remained relatively stable from April (7.7% (95% CI: 4.8% to 12.1%) to September (8.2% (95% CI: 5.7% to 11.6%)) and increased thereafter, reaching 19.7% (95% CI: 12.0% to 30.6%) in December 2020. 76 of 778 initially seronegative participants seroconverted during the follow-up (incidence: 205/1000 person-years). Among all seropositive individuals, 118/148 (80%) had a positive neutralisation test, 83/147 (56%) presented or reported a positive RT-qPCR, and 130/147 (88%) reported COVID-19-compatible symptoms at least once. However, only 46/73 (63%) of the seroconverters presented COVID-19-compatible symptoms in the month prior to seroconversion.

Conclusions

The seroprevalence among hospital HCW was slightly higher than that of the general Belgian population but followed a similar evolution, suggesting that infection prevention and control measures were effective and should be strictly maintained. After two SARS-CoV-2 waves, 80% of HCW remained seronegative, justifying their prioritisation in the vaccination strategy.

Trial registration number

NCT04373889

Article activity feed

  1. Version published to 10.1136/bmjopen-2021-050824
  2. ScreenIT

    SciScore for 10.1101/2020.10.03.20204545: (What is this?)

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

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Antibodies
    SentencesResources
    Presence of IgG antibodies in sera was tested using a commercially available semi-quantitative test from Euroimmun (anti-SARS-CoV-2 IgG ELISA, reference EI 2606-9601 G, Medizinische Labordiagnostika AG).
    anti-SARS-CoV-2 IgG
    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:
    Our study has several limitations. First, the characteristics of the ELISA test used might have led to a few diagnostic flaws. Follow-up of the HCWs in this study together with additional laboratory testing on stored samples (plaque reduction neutralisation) will likely give further insights in the extent of such diagnostic accuracy issues. Second, we cannot rule out the possibility of selection bias, as some of the initially selected participants may have refused to participate or were on sick leave at the time of the first sampling. The latter could have underestimated seroprevalence. The number of refusals was however reported to be very low, as at time of recruitment demand for testing in HCW was very high. Also, two of the selected hospitals entered the cohort in May and were not included in these baseline results, reducing the statistical power of the study. Recent evidence26,27 suggest that antibodies tend to wane in the early convalescent phase (8 weeks after infection), which means that HCW infected in the beginning of the epidemic might not have been detected. This could explain why in four participants who reported a previous positive PCR, no antibodies were detected. Finally, it should be noted that serological studies do not provide a complete picture of the immune response to SARS-CoV-2, in which T-cell mediated immunity seems to play an important role, especially in the long term.28,29 Still, the main strength of this study lies in the fact that its design allo...

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

    IdentifierStatusTitle
    NCT04373889Active, not recruitingCOVID-19 Among Healthcare Workers in Belgian Hospitals

    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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  3. Version published to 10.1101/2020.10.03.20204545 on medRxiv