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. 2023 Jun:43:100675.
doi: 10.1016/j.epidem.2023.100675. Epub 2023 Feb 26.

Empirical evidence of transmission over a school-household network for SARS-CoV-2; exploration of transmission pairs stratified by primary and secondary school

Senna C J L van Iersel  1 , Jantien A Backer  2 , Rolina D van Gaalen  2 , Stijn P Andeweg  2 , James D Munday  3 , Jacco Wallinga  4 , Albert Jan van Hoek  2 ; RIVM COVID-19 epidemiology and surveillance group
Affiliations

Empirical evidence of transmission over a school-household network for SARS-CoV-2; exploration of transmission pairs stratified by primary and secondary school

Senna C J L van Iersel et al. Epidemics. 2023 Jun.

Abstract

Background: Children play a key role in the transmission of many infectious diseases. They have many of their close social encounters at home or at school. We hypothesized that most of the transmission of respiratory infections among children occur in these two settings and that transmission patterns can be predicted by a bipartite network of schools and households.

Aim and methods: To confirm transmission over a school-household network, SARS-CoV-2 transmission pairs in children aged 4-17 years were analyzed by study year and primary/secondary school. Cases with symptom onset between 1 March 2021 and 4 April 2021 identified by source and contact-tracing in the Netherlands were included. In this period, primary schools were open and secondary school students attended class at least once per week. Within pairs, spatial distance between the postcodes was calculated as the Euclidean distance.

Results: A total of 4059 transmission pairs were identified; 51.9% between primary schoolers; 19.6% between primary and secondary schoolers; 28.5% between secondary schoolers. Most (68.5%) of the transmission for children in the same study year occurred at school. In contrast, most of the transmission of children from different study years (64.3%) and most primary-secondary transmission (81.7%) occurred at home. The average spatial distance between infections was 1.2 km (median 0.4) for primary school pairs, 1.6 km (median 0) for primary-secondary school pairs and 4.1 km (median 1.2) for secondary school pairs.

Conclusion: The results provide evidence of transmission on a bipartite school-household network. Schools play an important role in transmission within study years, and households play an important role in transmission between study years and between primary and secondary schools. Spatial distance between infections in a transmission pair reflects the smaller school catchment area of primary schools versus secondary schools. Many of these observed patterns likely hold for other respiratory pathogens.

Keywords: Children; Covid-19; Network; Transmission.

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Figures

Fig. 1
Fig. 1
Transmission pairs by class (primary school P1-P8, secondary school S1-S6) in the period between 1 March and 28 March for infectors and between 1 March and 4 April for infectees. The size of the bubbles shows the number of pairs per setting. Transmission pairs with an unknown setting are excluded. The color of the bubbles indicates the fraction of transmission (the fractions of the three settings Home, School and Other add up to one for each school year combination) in A - the home setting. B - the school setting. C - other settings than household and school setting.
Fig. 2
Fig. 2
Chord-diagram showing the absolute difference in transmission pairs between school years (difference A→B, A←B). Only those arrows are shown for which there is a significant asymmetry in the direction of pairs. Colors indicate the infector age class.
Fig. 3
Fig. 3
Mean distances in kilometers for primary and secondary school transmission pair combinations with confidence interval. Red bars indicate mean distances without transmission pairs within the same PC6 (zero distance), blue bars indicate mean distances including transmission pairs within the same PC6.
Fig. 4
Fig. 4
Transmission chains with frequency of infections between primary and secondary school, with at least one infected child not living in the same household as the others. Only chains are shown where the setting of transmission of the first pair in the chain is either ‘home’ or ‘school’, with the setting of transmission for the second pair in the chain being the other of the two settings. Red indicates that the transmission of the first pair took place in the ‘home’ setting and thus the transmission setting of the second pair is ‘school’. For blue, it is the other way around. Percentages on the right indicate what part of triplets consists of only secondary (S), primary and secondary (in any order, P + S) or only primary school children (P).
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