Transmission of SARS-CoV-2 following exposure in school settings: experience from two Helsinki area exposure incidents.
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Abstract
Background
The role of children in SARS-CoV-2 transmission is unclear. We investigated two COVID-19 school exposure incidents in the Helsinki area.
Methods
We conducted two retrospective cohort studies after schools exposures, with a household transmission extension. We defined a case as an exposed person with either a positive RT-PCR, or positive microneutralisation testing (MNT) as confirmation of SARS-CoV-2 nucleoprotein IgG antibodies detection via fluorescent microsphere immunoassay (FMIA). We recruited close school contacts and families of school cases, calculated attack rates (AR) on school level and families, and identified transmission chains.
Findings
In incident A, the index was a pupil. Participation rate was 74% (89/121), and no cases were identified. In incident B, the index was a member of school personnel. Participation rate was 81% (51/63). AR was 16% (8/51): 6 pupils and 1 member of school personnel were MNT and FMIA positive; 1 pupil had a positive RT-PCR, but negative serology samples. We visited all school cases’ families (n=8). The AR among close household contacts was 42% (9/20 in 3/8 families) but other plausible sources were always reported. At three months post-exposure, 6/8 school cases were re-sampled and still MNT positive.
Interpretation
When the index was a child, no school transmission was identified, while the occurrence of an adult case led to a 16% AR. Further cases were evidenced in 3 families, but other transmission chains were plausible. It is likely that transmission from children to adults is limited.
Funding
The Finnish Institute for Health and Welfare funded this study.
Research in context
Evidence before the study
The first autochthonous case of COVID-19 in Finland was identified on February 29 th . Transmission of the virus has led to more than 7250 cases and over 300 deaths (As of July 12 th 2020). On March 16 th , assuming that children might have a role in transmission, the Finnish government ordered school closures, to the exclusion of pre-school and grades 1-3. Schools were closed from March 18 and reopened on May 14 th . At the stage of closure, a very limited number of reports of school related COVID-19 clusters or exposure incidents had been published, and the potential extent of transmission in a school setting was unknown.
Added value of this study
We investigated two exposure incidents in two different schools from the Helsinki area to assess transmission among pupils, school personnel and household contacts of identified cases. In school A, contact with a COVID-19 pupil did not lead to further transmission, while in school B, out of 51 recruited contacts, eight (16%) were proved to have had COVID-19 infection, including one member of staff. Among the close household contacts of pupils who were tested positive, COVID-19 attack rate was 31% (5/16). However, in all investigated households, other sources of infections were plausible; hence household transmission following a pediatric COVID-19 case appears to be limited.
Implications of all of the available evidence
Incidence of COVID-19 infections in children following school related exposure was limited, as well as secondary transmission within their household. We hope our findings will help prioritize mitigation measures as well as reduce worry among parents of school aged children as most EU countries are preparing for the start of a new school year in autumn.
Article activity feed
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SciScore for 10.1101/2020.07.20.20156018: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement IACUC: 7 Ethical requirements: The Finnish communicable diseases law and the law on the duties of the Finnish Institute for Health and Welfare allowed the implementation of this research without seeking further institutional ethical review.
Consent: 8,9 Informed consent was obtained from all cases and contacts willing to participate in the investigation, before any procedure was performed as part of the investigation.Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources Statistical analysis was performed using Stata 15 (StataCorp LP Lakeway, … SciScore for 10.1101/2020.07.20.20156018: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement IACUC: 7 Ethical requirements: The Finnish communicable diseases law and the law on the duties of the Finnish Institute for Health and Welfare allowed the implementation of this research without seeking further institutional ethical review.
Consent: 8,9 Informed consent was obtained from all cases and contacts willing to participate in the investigation, before any procedure was performed as part of the investigation.Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Software and Algorithms Sentences Resources Statistical analysis was performed using Stata 15 (StataCorp LP Lakeway, TX, USA), while transmission chains were designed using the R package epicontacts. StataCorpsuggested: (Stata, RRID:SCR_012763)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:Finally, a limitation of this work is the rather small sample size: 89 participants in exposure incident A and 51 in incident B, however, the 76% participation rate obtained in the initial investigation, and 100% in the household transmission study does improve the representativeness of our findings. We were only made aware of one additional COVID-19 case among close contacts who did not participate to the study.
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.
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SciScore for 10.1101/2020.07.20.20156018: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement 7 Ethical requirements The Finnish communicable diseases law and the law on the duties of the Finnish Institute for Health and Welfare allowed the implementation of this research without seeking further institutional ethical review. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Antibodies Sentences Resources Antigen was conjugated on MagPlex Microspheres and bound IgG antibodies were identified by a fluorescently labeled conjugated antibody (R- Phycoerythrin-conjugated Goat Anti-Human IgG, Jackson Immuno Research, Luminex® MAGPIX® system. USA). …SciScore for 10.1101/2020.07.20.20156018: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement 7 Ethical requirements The Finnish communicable diseases law and the law on the duties of the Finnish Institute for Health and Welfare allowed the implementation of this research without seeking further institutional ethical review. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Antibodies Sentences Resources Antigen was conjugated on MagPlex Microspheres and bound IgG antibodies were identified by a fluorescently labeled conjugated antibody (R- Phycoerythrin-conjugated Goat Anti-Human IgG, Jackson Immuno Research, Luminex® MAGPIX® system. USA). Anti-Human IgGsuggested: NoneOut of 42 pupils, 6 (14%) were found to have neutralizing antibodies and IgG antibodies to SARS-CoV-2 nucleoprotein, while 2 pupils had low levels (3·6 and 8·7 U/ml) of IgG antibodies to SARS-CoV-2 nucleoprotein measured by FMIA in the absence of neutralizing antibodies, hence were not considered as cases. have neutralizing antibodies and IgGsuggested: NoneSARS-CoV-2 nucleoprotein, while 2suggested: NoneSoftware and Algorithms Sentences Resources The specificity and sensitivity of the assay was assessed by plotting a receiver operating characteristic (ROC) curve using the statistical software (GraphPad Prism 8). GraphPadsuggested: (GraphPad Prism, RRID:SCR_002798)Statistical analysis was performed using Stata 15 (StataCorp LP Lakeway, TX, USA), while transmission chains were designed using the R package epicontacts. StataCorpsuggested: (Stata, RRID:SCR_012763)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:
Finally, a limitation of this work is the rather small sample size: 89 participants in exposure incident A and 51 in incident B, however, the 76% participation rate obtained in the initial investigation, and 100% in the household transmission study does improve the representativeness of our findings. We were only made aware of one additional COVID-19 case among close contacts who did not participate to the study. Conclusion We found that exposure in school due to a child index case with mild symptoms led to no further cases among the close contacts, whereas exposure to an adult index case with moderate symptoms in a school setting led to secondary transmission. The outcome is most likely a result of several factors including the age of the index case, the degree of symptoms, and the type of contact. Further studies on COVID-19 transmission in a school setting are required in order to better advice on mitigation measures such as quarantine and school closure. Starting from August 2020, the Finnish Institute for Health and Welfare will be coordinating multisite transmission studies in the five university hospital cities to further understand the role of children in SARS-CoV- 2 transmission chains and the role of immunity and other factors in this process. Authors’ contributions TD, ES, NI, MM, and HN conceived and designed the study. EE, AJ and TL conducted contact tracing. TD, LH, ES, and HN recruited participants to the study. NI developed, supervised and interpreted the virological analysis, PÖ cultivated the viral strains for immunological analyses. CV, AH, and MM developed, performed, supervised and interpreted the immunological analyses. TD performed the statistical analyses. TD and EE wrote the first version of the report. All authors critically reviewed and approved the final version of the report Declaration of interests We declare no competing interests.
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.
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 is not a substitute for expert review. SciScore checks for the presence and correctness of RRIDs (research resource identifiers) in the manuscript, and detects sentences that appear to be missing RRIDs. SciScore also checks to make sure that rigor criteria are addressed by authors. It does this by detecting sentences that discuss criteria such as blinding or power analysis. SciScore does not guarantee that the rigor criteria that it detects are appropriate for the particular study. Instead it assists authors, editors, and reviewers by drawing attention to sections of the manuscript that contain or should contain various rigor criteria and key resources. For details on the results shown here, including references cited, please follow this link.
-
SciScore for 10.1101/2020.07.20.20156018: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement 7 Ethical requirements The Finnish communicable diseases law and the law on the duties of the Finnish Institute for Health and Welfare allowed the implementation of this research without seeking further institutional ethical review. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Antibodies Sentences Resources We two retrospective defined a case cohort as an studies after exposed schools person exposures, with either a with a household positive RT-PCR, transmission or positive microneutralisation testing (MNT) as confirmation of SARS-CoV-2 nucleoprotein IgG … SciScore for 10.1101/2020.07.20.20156018: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
Institutional Review Board Statement 7 Ethical requirements The Finnish communicable diseases law and the law on the duties of the Finnish Institute for Health and Welfare allowed the implementation of this research without seeking further institutional ethical review. Randomization not detected. Blinding not detected. Power Analysis not detected. Sex as a biological variable not detected. Table 2: Resources
Antibodies Sentences Resources We two retrospective defined a case cohort as an studies after exposed schools person exposures, with either a with a household positive RT-PCR, transmission or positive microneutralisation testing (MNT) as confirmation of SARS-CoV-2 nucleoprotein IgG antibodies detection via fluorescent microsphere immunoassay (FMIA). SARS-CoV-2 nucleoprotein IgGsuggested: NoneAntigen was conjugated on MagPlex Microspheres and bound IgG antibodies were identified by a fluorescently labeled conjugated antibody (R- Phycoerythrin-conjugated Goat Anti-Human IgG, Jackson Immuno Research, Luminex® MAGPIX® system. USA). Anti-Human IgGsuggested: NoneNone of the 87 serum samples had detectable SARS-CoV-2-specific neutralizing antibodies nor IgG antibodies to SARS-CoV-2 nucleoprotein. SARS-CoV-2-specific neutralizing antibodies nor IgGsuggested: None<div style="margin-bottom:8px"> <div><b>SARS-CoV-2 nucleoprotein.</b></div> <div>suggested: (Sino Biological Cat# 40143-R019, <a href="https://scicrunch.org/resources/Any/search?q=AB_2827973">AB_2827973</a>)</div> </div> </td></tr><tr><td style="min-width:100px;vertical-align:top;border-bottom:1px solid lightgray">Out of 42 pupils, 6 (14%) were found to have neutralizing antibodies and IgG antibodies to SARS-CoV-2 nucleoprotein, while 2 pupils had low levels (3·6 and 8·7 U/ml) of IgG antibodies to SARS-CoV-2 nucleoprotein measured by FMIA in the absence of neutralizing antibodies, hence were not considered as cases.</td><td style="min-width:100px;border-bottom:1px solid lightgray"> <div style="margin-bottom:8px"> <div><b>have neutralizing antibodies and IgG</b></div> <div>suggested: None</div> </div> <div style="margin-bottom:8px"> <div><b>SARS-CoV-2 nucleoprotein, while 2</b></div> <div>suggested: None</div> </div> </td></tr><tr><td style="min-width:100px;text-align:center; padding-top:4px;" colspan="2"><b>Software and Algorithms</b></td></tr><tr><td style="min-width:100px;text=align:center"><i>Sentences</i></td><td style="min-width:100px;text-align:center"><i>Resources</i></td></tr><tr><td style="min-width:100px;vertical-align:top;border-bottom:1px solid lightgray">The specificity and sensitivity of the assay was assessed by plotting a receiver operating characteristic (ROC) curve using the statistical software (GraphPad Prism 8).</td><td style="min-width:100px;border-bottom:1px solid lightgray"> <div style="margin-bottom:8px"> <div><b>GraphPad</b></div> <div>suggested: (GraphPad Prism, <a href="https://scicrunch.org/resources/Any/search?q=SCR_002798">SCR_002798</a>)</div> </div> </td></tr><tr><td style="min-width:100px;vertical-align:top;border-bottom:1px solid lightgray">Statistical analysis was performed using Stata 15 (StataCorp LP Lakeway, TX, USA), while transmission chains were designed using the R package epicontacts.</td><td style="min-width:100px;border-bottom:1px solid lightgray"> <div style="margin-bottom:8px"> <div><b>StataCorp</b></div> <div>suggested: (Stata, <a href="https://scicrunch.org/resources/Any/search?q=SCR_012763">SCR_012763</a>)</div> </div> </td></tr></table>Data from additional tools added to each annotation on a weekly basis.
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 is not a substitute for expert review. SciScore checks for the presence and correctness of RRIDs (research resource identifiers) in the manuscript, and detects sentences that appear to be missing RRIDs. SciScore also checks to make sure that rigor criteria are addressed by authors. It does this by detecting sentences that discuss criteria such as blinding or power analysis. SciScore does not guarantee that the rigor criteria that it detects are appropriate for the particular study. Instead it assists authors, editors, and reviewers by drawing attention to sections of the manuscript that contain or should contain various rigor criteria and key resources. For details on the results shown here, including references cited, please follow this link.
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