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. 2022 Aug 31;10(4):e0062222.
doi: 10.1128/spectrum.00622-22. Epub 2022 Jul 6.

Symptomatic and Asymptomatic Transmission of SARS-CoV-2 in K-12 Schools, British Columbia, Canada April to June 2021

Alexandra Choi  1 , Louise C Mâsse  2   3 , Samantha Bardwell  4 , Iryna Kayda  5 , Yanjie Zhao  1 , Yang Xin Zi Xu  1 , Ani Markarian  1 , Daniel Coombs  4 , Adrienne Macdonald  6 , Allison W Watts  7 , Nalin Dhillon  6 , Michael Irvine  8 , Collette O'Reilly  9 , Pascal M Lavoie  2   7   10 , David M Goldfarb  2   10   11
Affiliations

Symptomatic and Asymptomatic Transmission of SARS-CoV-2 in K-12 Schools, British Columbia, Canada April to June 2021

Alexandra Choi et al. Microbiol Spectr. .

Abstract

We prospectively studied SARS-CoV-2 transmission at schools in an era of variants of concern, offering all close contacts serial viral asymptomatic testing up to 14 days. From the 69 primary cases detected in schools, 392 close contacts were identified and offered asymptomatic testing. A total of 229 (58%) were close school contacts, and of these, 3 tested positive (1.3%), 2 of which were detected through asymptomatic testing. This is in contrast to the 117 household contacts, where 43 (37%) went on to become secondary cases. Routine asymptomatic testing of close contacts should be examined in the context of local testing rates, preventive measures, programmatic costs, and health impacts of asymptomatic transmission. IMPORTANCE There is concern that schools may be a setting where asymptomatic infections might result in significant "silent" transmission of SARS-CoV-2, particularly after the emergence of more transmissible variants of concern. After the programmatic implementation of a strategy of asymptomatic testing of close COVID-19 contacts as part of contact tracing in the school setting, the majority of the secondary cases were still found to have occurred in home or social contacts. However, for the 6.2% of secondary cases that occurred in close school contacts, the majority were detected through asymptomatic testing. The potential added yield of this approach needs to be considered within the overall setting, including consideration of the local epidemiology, ongoing goals of case and contact management, additional costs, logistical challenges for families, and possible health impacts of asymptomatic transmission.

Keywords: COVID-19; SARS-CoV-2; asymptomatic; school; transmission.

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Conflict of interest statement

The authors declare a conflict of interest. C.O’R. is an employee of the Vancouver School District, but the District was not involved in the design, analysis, interpretation of the data or the drafting of this manuscript. Rest of the authors declare no conflict of interest.

Figures

FIG 1
FIG 1
Flow diagram of close contacts who became cases and who did not by contact type. Other contacts comprise 48% social (N = 22), 7% extracurricular (N = 3), 35% mixed school and social (N = 16), and 10% unidentified (N = 5).
FIG 2
FIG 2
Flow chart of asymptomatic testing participation and test results.
See this image and copyright information in PMC

References

    1. Bark D, Dhillon N, St-Jean M, Kinniburgh B, McKee G, Choi A. 2021. SARS-CoV-2 transmission in kindergarten to grade 12 schools in the Vancouver Coastal Health region: a descriptive epidemiologic study. Cmajo 9:E810–E817. doi: 10.9778/cmajo.20210106. - DOI - PMC - PubMed
    1. Irfan O, Li J, Tang K, Wang Z, Bhutta ZA. 2021. Risk of infection and transmission of SARS-CoV-2 among children and adolescents in households, communities and educational settings: a systematic review and meta-analysis. J Glob Health 11:e05013. doi: 10.7189/jogh.11.05013. - DOI - PMC - PubMed
    1. Mehta NS, Mytton OT, Mullins EWS, Fowler TA, Falconer CL, Murphy OB, Langenberg C, Jayatunga WJP, Eddy DH, Nguyen-Van-Tam JS. 2020. SARS-CoV-2 (COVID-19): what do we know about children? A systematic review. Clin Infect Dis 71:2469–2479. doi: 10.1093/cid/ciaa556. - DOI - PMC - PubMed
    1. Brandal LT, Ofitserova TS, Meijerink H, Rykkvin R, Lund HM, Hungnes O, Greve-Isdahl M, Bragstad K, Nygård K, Winje BA. 2021. Minimal transmission of SARS-CoV-2 from paediatric COVID-19 cases in primary schools, Norway, August to November 2020. Euro Surveill 26:2002011. doi: 10.2807/1560-7917.ES.2020.26.1.2002011. - DOI - PMC - PubMed
    1. Hershow RB, Wu K, Lewis NM, Milne AT, Currie D, Smith AR, Lloyd S, Orleans B, Young EL, Freeman B, Schwartz N, Bryant B, Espinosa C, Nakazawa Y, Garza E, Almendares O, Abara WE, Ehlman DC, Waters K, Hill M, Risk I, Oakeson K, Tate JE, Kirking HL, Dunn A, Vallabhaneni S, Hersh AL, Chu VT. 2021. Low SARS-CoV-2 transmission in elementary schools—Salt Lake County, Utah, December 3, 2020–January 31, 2021. MMWR Morb Mortal Wkly Rep 70:442–448. doi: 10.15585/mmwr.mm7012e3. - DOI - PMC - PubMed

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