Safety of SARS-CoV-2 test-to-stay in daycare: a regression discontinuity in time analysis

Background and Objectives Test-to-stay concepts apply serial testing of children in daycare after exposure to SARS-CoV-2 without use of quarantine. This study aims to assess safety of a test-to-stay screening in daycare facilities. Methods 714 daycare facilities and approximately 50,000 children ≤6 years in Cologne, Germany participated in a SARS-CoV-2 Pool-PCR screening from March 2021 to April 2022. The screening initially comprised post-exposure quarantine and was adapted to a test-to-stay approach during its course. To assess safety of the test-to-stay approach, we explored potential changes in frequencies of infections among children following the adaptation to the test-to-stay approach by applying regression discontinuity in time (RDiT) analyses. To this end, PCR-test data were linked with routinely collected data on reported infections in children and analyzed using ordinary least squares regressions. Results 219,885 Pool-PCRs and 352,305 Single-PCRs were performed. 6,440 (2.93%) Pool-PCRs tested positive, and 17,208 infections in children were reported. We estimated that during a period of 30 weeks, the test-to-stay concept avoided between 7 and 20 days of quarantine per eligible daycare child. RDiT revealed a 26% reduction (Exp. Coef: 0.74, CI:0.52;1.06) in infection frequency among children and indicated no significant increase attributable to the test-to-stay approach. This result was not sensitive to adjustments for 7-day incidence, season, SARS-CoV-2 variant, and socioeconomic status. Conclusion Our analyses provide evidence that suggest safety of the test-to-stay approach compared to traditional quarantine measures. This approach offers a promising option to avoid use of quarantine after exposure to respiratory pathogens in daycare settings. ### Competing Interest Statement Felix Dewald, Florian Klein and Rolf Kaiser hold EU-wide trademark protection for the terms Lolli-Test (018503959) and Lolli-Methode (018503958). All authors have no competing interests. ### Funding Statement Funding was provided by the German Ministry of Education and Research (BMBF) (registration number: 01KX2021) within Bundesweites Forschungsnetz Angewandte Surveillance und Testung (B-FAST) project of the NaFoUniMedCovid19 consortium. Furthermore, funding was provided by the Bundesministerium fuer Bildung und Forschung (registration number: ZMI1-2521COR004) and by the German Research Foundation (DFG, CRC 1310). Additionally, funding was provided by EURCARE, EU grant No. 101046016. Finally, we acknowledge support for the Article Processing Charge from the DFG (German Research Foundation, 491454339). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: All analyses were performed under a protocol approved by the institutional review board of the Medical Faculty of the University of Cologne (21-1358). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Deidentified PCR test data (including data dictionaries) will be made available, in addition to study protocols, the statistical analysis plan, and the code for analysis. The data and code will be made available upon publication to researchers who provide a methodologically sound proposal for use in achieving the goals of the approved proposal. Proposals should be submitted to felix.dewald@uk-koeln.de. * COVID-19 : Coronavirus disease 2019 SARS-CoV-2 : severe acute respiratory syndrome coronavirus type 2 PCR : polymerase chain reaction RDiT : regression discontinuity in time MSE : mean squared error SES : socioeconomic status IQR : inter-quartile range RKI : Robert Koch Institute