High SARS-CoV-2 seroprevalence in children and adults in the Austrian ski resort of Ischgl

  1. Ludwig Knabl
  2. Tanmay Mitra
  3. Janine Kimpel
  4. Annika Rössler
  5. André Volland
  6. Andreas Walser
  7. Hanno Ulmer
  8. Lisa Pipperger
  9. Sebastian C. Binder
  10. Lydia Riepler
  11. Katie Bates
  12. Arnab Bandyopadhyay
  13. Marta Schips
  14. Mrinalini Ranjan
  15. Barbara Falkensammer
  16. Wegene Borena
  17. Michael Meyer-Hermann
  18. Dorothee von Laer

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Abstract

Background

In early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe.

Methods

Between April 21 st and 27 th 2020, a cross-sectional epidemiologic study targeting the full population of Ischgl ( n  = 1867), of which 79% could be included ( n  = 1473, incl. 214 children), was performed. For each individual, the study involved a SARS-CoV-2 PCR, antibody testing and structured questionnaires. A mathematical model was used to help understand the influence of the determined seroprevalence on virus transmission.

Results

The seroprevalence was 42.4% (95% confidence interval (CI) 39.8–44.7). Individuals under 18 showed a significantly lower seroprevalence of 27.1% (95% CI 21.3-33.6) than adults (45%; 95% CI 42.2–47.7; OR of 0.455, 95% CI 0.356–0.682, p  < 0.001). Of the seropositive individuals, 83.7% had not been diagnosed to have had SARS-CoV-2 infection previously. The clinical course was generally mild. Over the previous two months, two COVID-19-related deaths had been recorded, corresponding to an infection fatality rate of 0.25% (95% CI 0.03–0.91). Only 8 (0.5 %) individuals were newly diagnosed to be infected with SARS-CoV-2 during this study.

Conclusions

Ischgl was hit early and hard by SARS-CoV-2 leading to a high local seroprevalence of 42.4%, which was lower in individuals below the age of 18 than in adults. Mathematical modeling suggests that a drastic decline of newly infected individuals in Ischgl by the end of April occurred due to the dual impact from the non-pharmacological interventions and a high immunization of the Ischgl population.

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  1. Version published to 10.1038/s43856-021-00007-1
  2. ScreenIT

    SciScore for 10.1101/2020.08.20.20178533: (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
    The participants were screened for anti-SARS-CoV-2 antibodies as well as for SARS-CoV-2 virus in nasopharyngeal swabs by 3 immunoassays for binding antibodies, a neutralization antibody assay (nAb-assay) and an RT-PCR, respectively.
    anti-SARS-CoV-2
    suggested: None
    SARS-CoV-2-PCR, anti-SARS-CoV-2-antibody tests: RT-PCR for the detection of SARS-CoV-2 was performed using the RealStar® SARS-CoV-2 RT-PCR kit 1.0 (Altona Diagnostics GmbH, Hamburg, Germany).
    SARS-CoV-2-PCR
    suggested: None
    Neutralizing antibody-assay: Neutralizing antibody (nAb)-assays using highly SARS-CoV-2 susceptible cells9 were performed as described in detail in the supplement.
    antibody-assay
    suggested: None
    We tested all 50 anti-S IgG+/anti-N IgG+ positive children, 148 randomly selected currently PCR-negative adults that were positive for anti-S IgG as well as anti-N-IgG, all PCR-negative subjects with discrepant antibody results (n = 38 for anti-S IgG+/anti-N IgG- and n = 36 for anti-S IgG-/anti-N IgG+) or with solely anti-S IgA positive ELISA results (n = 26).
    anti-S IgG+/anti-N IgG+
    suggested: None
    anti-S IgG+/anti-N IgG-
    suggested: None
    anti-S IgG-/anti-N IgG+
    suggested: None
    anti-S IgA
    suggested: None
    Therefore, all sera were tested in two different antibody assays and samples that were positive in both anti-S IgG and anti-N-IgG antibody assays were not all retested by the neutralizing antibody assay.
    anti-S IgG
    suggested: None
    anti-N-IgG
    suggested: None
    Software and Algorithms
    SentencesResources
    Participants’ sera were screened for anti-SARS-CoV-2-S1-protein IgA and IgG positivity by a commercially available anti-SARS-CoV-2-IgA and -IgG ELISA (Euroimmun, Lübeck, Germany), respectively, and for anti-SARS-CoV-2-N-protein IgG (anti-N IgG) with the Abbott SARS-CoV-2 IgG immunoassay (Abbott, Illinois, USA).
    Abbott
    suggested: (Abbott, RRID:SCR_010477)

    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, the analysis does not allow for a precise quantitative evaluation of the herd-immunity threshold because of several limitations in the data. Subjective reporting of symptom onset dates as well as an unclear attribution of symptoms to SARS-CoV-2 infections are major sources of uncertainty. It is not known whether a fraction of the population, in particular, of the children, might combat the viral infection by innate immune responses alone without developing specific antibodies, thus, appearing seronegative in the current study. Further, the prevalence of super-spreading-events in Ischgl might impact on the mathematical analysis. Beyond our assumption of homogeneous mixing of the Ischgl residents and tourists, the precise impact of the in- and out-flow of tourists, who participated in infection chains and then left following their stay in Ischgl as well as during the exodus around March 13th, 2020, on the mathematical analysis cannot be assessed properly in the absence of data on the serostatus of the tourists. While the relative impact of leaving tourists and NPIs are difficult to disentangle, the drastic decline in the time-dependent reproduction number can be explained by the combination of both together with a significant immunization of the Ischgl population. The high seroprevalence alone does not explain the successful limitation of virus transmission. Population heterogeneity in terms of inherent innate and T-cell immunity, however, might further reduce the herd...

    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.
    • No funding statement was detected.
    • No protocol registration statement was detected.

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  3. Version published to 10.1101/2020.08.20.20178533 on medRxiv