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. 2022 Dec 26;22(1):960.
doi: 10.1186/s12879-022-07904-3.

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

Lotte Jonker  1 , Kimberly J Linde  2 , Marieke L A de Hoog  3 , Robin Sprado  3 , Robin C Huisman  4 , Richard Molenkamp  4 , Bas B Oude Munnink  4 , Wietske Dohmen  2 , Dick J J Heederik  2 , Dirk Eggink  5 , Matthijs R A Welkers  5   6 , Harry Vennema  5 , Pieter L A Fraaij  4   7 , Marion P G Koopmans  4 , Inge M Wouters  2 , Patricia C J L Bruijning-Verhagen  3
Affiliations

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

Lotte Jonker et al. BMC Infect Dis. .

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.

Keywords: Air levels; Outbreak; SARS-CoV-2; Secondary schools; Transmission.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Overview of participating schools and school contacts. Number of SARS-CoV-2 infections among school contacts and positive air and surface samples are depicted per outbreak study. No environmental samples were taken during outbreak A
Fig. 2
Fig. 2
Ct-values by day since last exposure for nose throat swabs and saliva (n = 46). Ct-values by day since last exposure for nose throat swabs (orange) and saliva (blue). All samples from subjects with at least one positive results are included. Negative results are displayed as Ct-value > 45
Fig. 3
Fig. 3
Sequencing data of RT-PCR positive saliva and nose throat swabs within school A and C. NTS Nose throat swab. Both test rounds are included in the figure. If sequencing data was available for both test rounds, only the sequence of the first round is included in the phylogenetic tree. Identification of NTS samples are depicted in red and for saliva samples in black
See this image and copyright information in PMC

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