Prevalence of SARS-CoV-2 in Household Members and Other Close Contacts of COVID-19 Cases: A Serologic Study in Canton of Vaud, Switzerland

  1. Julien Dupraz
  2. Audrey Butty
  3. Olivier Duperrex
  4. Sandrine Estoppey
  5. Vincent Faivre
  6. Julien Thabard
  7. Claire Zuppinger
  8. Gilbert Greub
  9. Giuseppe Pantaleo
  10. Jérôme Pasquier
  11. Valentin Rousson
  12. Malik Egger
  13. Amélie Steiner-Dubuis
  14. Sophie Vassaux
  15. Eric Masserey
  16. Murielle Bochud
  17. Semira Gonseth Nusslé
  18. Valérie D’Acremont

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Abstract

Background

Research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission within households and other close settings using serological testing is scarce.

Methods

We invited coronavirus disease 2019 (COVID-19) cases diagnosed between February 27 and April 1, 2020, in Canton of Vaud, Switzerland, to participate, along with household members and other close contacts. Anti-SARS-CoV-2 immunoglobulin G antibodies were measured using a Luminex immunoassay. We estimated factors associated with serological status using generalized estimating equations.

Results

Overall, 219 cases, 302 household members, and 69 other close contacts participated between May 4 and June 27, 2020. More than half of household members (57.2%; 95% CI, 49.7%–64.3%) had developed a serologic response to SARS-CoV-2, while 19.0% (95% CI, 10.0%–33.2%) of other close contacts were seropositive. After adjusting for individual and household characteristics, infection risk was higher in household members aged ≥65 years than in younger adults (adjusted odds ratio [aOR], 3.63; 95% CI, 1.05–12.60) and in those not strictly adhering to simple hygiene rules like hand washing (aOR, 1.80; 95% CI, 1.02–3.17). The risk was lower when more than 5 people outside home were met during semiconfinement, compared with none (aOR, 0.35; 95% CI, 0.16–0.74). Individual risk of household members to be seropositive was lower in large households (22% less per each additional person).

Conclusions

During semiconfinement, household members of a COVID-19 case were at very high risk of getting infected, 3 times more than close contacts outside home. This highlights the need to provide clear messages on protective measures applicable at home. For elderly couples, who were especially at risk, providing external support for daily basic activities is essential.

Article activity feed

  1. Version published to 10.1093/ofid/ofab149
  2. ScreenIT

    SciScore for 10.1101/2020.11.27.20239244: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementIRB: The Cantonal Ethics Committee of Vaud, Switzerland (ID 2020-00887) approved the protocol.
    Consent: All participants (or their legal representative) provided written informed consent.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    Detection of anti-SARS-CoV-2 antibodies: We measured anti-SARS-CoV-2 IgG antibodies targeting the spike (S) protein in its native trimeric form using a Luminex immunoassay.
    anti-SARS-CoV-2
    suggested: None
    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:
    Limitations need to be acknowledged. The Swiss testing policy during the first epidemic wave, which limited diagnostic testing mainly to individuals at increased risk for severe illness, made the sample of index cases not representative of all cases that occurred in the community during this period. Index cases were thus not necessarily the first infected in their household, but those fulfilling testing criteria. However, this would be especially problematic if the purpose were to identify factors associated with infectivity of the index case, which we deliberately avoided. Incidence of new COVID-19 cases remains high worldwide and prevention of transmission is, for now, the only way to tackle the pandemic. If concerns regarding the transmission of SARS-CoV-2 in shops, restaurants and public gatherings are justified, our findings emphasise that the risk of being infected is much higher at home. In this regard, trying to prevent transmission within households through the dissemination of clear messages on how to protect each other at home is key. However, this remains overlooked in collective awareness and public health discourse, precisely because quarantine and confinement are methods used to break the transmission chain. Early testing of the first case in a household is also important to support immediate self-isolation within the house. Our results suggest in particular that it is essential for non-institutionalised elderly couples to receive strong external support for da...

    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. ScreenIT

    SciScore for 10.1101/2020.11.27.20239244: (What is this?)

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

    Table 1: Rigor

    Institutional Review Board StatementThe Cantonal Ethics Committee of Vaud, Switzerland (ID 2020-00887) approved the protocol.Randomizationnot detected.Blindingnot detected.Power Analysisnot detected.Sex as a biological variableResults Two-hundred and nineteen index cases (49·0%), aged 2 to 90 years (mean 48·7, SD 19·3), participated in the study, of which 55·7% considered themselves as women.

    Table 2: Resources

    Antibodies
    SentencesResources
    Anti-SARS-CoV- 2 IgG antibodies were measured using a Luminex immunoassay.
    Anti-SARS-CoV- 2 IgG
    suggested: None
    Detection of anti-SARS-CoV-2 antibodies We measured anti-SARS-CoV-2 IgG antibodies targeting the spike (S) protein in its native trimeric form using a Luminex immunoassay.
    anti-SARS-CoV-2
    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:

    Limitations need to be acknowledged. The Swiss testing policy during the first epidemic wave, which limited diagnostic testing mainly to individuals at increased risk for severe illness, made the sample of index cases not representative of all cases that occurred in the community during this period. Index cases were thus not necessarily the first infected in their household, but those fulfilling testing criteria. However, this would be especially problematic if the purpose were to identify factors associated with infectivity of the index case, which we deliberately avoided. Incidence of new COVID-19 cases remains high worldwide and prevention of transmission is, for now, the only way to tackle the pandemic. If concerns regarding the transmission of SARS-CoV-2 in shops, restaurants and public gatherings are justified, our findings emphasise that the risk of being infected is much higher at home. In this regard, trying to prevent transmission within households through the dissemination of clear messages on how to protect each other at home is key. However, this remains overlooked in collective awareness and public health discourse, precisely because quarantine and confinement are methods used to break the transmission chain. Early testing of the first case in a household is also important to support immediate self-isolation within the house. Our results suggest in particular that it is essential for non-institutionalised elderly couples to receive strong external support for da...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We found bar graphs of continuous data. We recommend replacing bar graphs with more informative graphics, as many different datasets can lead to the same bar graph. The actual data may suggest different conclusions from the summary statistics. For more information, please see Weissgerber et al (2015).

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

    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.

  4. Version published to 10.1101/2020.11.27.20239244v1 on medRxiv