SARS-CoV-2 outbreaks in secondary school settings in the Netherlands during fall 2020; silent circulation

Lotte Jonker*, Kimberly J. Linde, Marieke L.A. de Hoog, Robin Sprado, Robin C. Huisman, Richard Molenkamp, Bas B. Oude Munnink, Wietske Dohmen, Dick J.J. Heederik, Dirk Eggink, Matthijs R.A. Welkers, Harry Vennema, Pieter L.A. Fraaij, Marion P.G. Koopmans, Inge M. Wouters, Patricia C.J.L. Bruijning-Verhagen

*Corresponding author for this work

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Abstract

Background: In fall 2020 when schools in the Netherlands operated under a limited set of COVID-19 measures, we conducted outbreaks studies in four secondary schools to gain insight in the level of school transmission and the role of SARS-CoV-2 transmission via air and surfaces. Methods: Outbreak studies were performed between 11 November and 15 December 2020 when the wild-type variant of SARS-CoV-2 was dominant. Clusters of SARS-CoV-2 infections within schools were identified through a prospective school surveillance study. All school contacts of cluster cases, irrespective of symptoms, were invited for PCR testing twice within 48 h and 4–7 days later. Combined NTS and saliva samples were collected at each time point along with data on recent exposure and symptoms. Surface and active air samples were collected in the school environment. All samples were PCR-tested and sequenced when possible. Results: Out of 263 sampled school contacts, 24 tested SARS-CoV-2 positive (secondary attack rate 9.1%), of which 62% remained asymptomatic and 42% had a weakly positive test result. Phylogenetic analysis on 12 subjects from 2 schools indicated a cluster of 8 and 2 secondary cases, respectively, but also other distinct strains within outbreaks. Of 51 collected air and 53 surface samples, none were SARS-CoV-2 positive. Conclusion: Our study confirmed within school SARS-CoV-2 transmission and substantial silent circulation, but also multiple introductions in some cases. Absence of air or surface contamination suggests environmental contamination is not widespread during school outbreaks.

Original languageEnglish
Article number960
JournalBMC Infectious Diseases
Volume22
Issue number1
DOIs
Publication statusPublished - 26 Dec 2022

Bibliographical note

Funding Information:
This work was supported in part by ZonMw; Project number 10430022010024. The funder was not involved in the design of the study, collection, analysis and interpretation of data and in writing of the manuscript.

Publisher Copyright:
© 2022, The Author(s).

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