{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T06:22:59Z","timestamp":1787638979479,"version":"build-2736575974"},"reference-count":105,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T00:00:00Z","timestamp":1787616000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Public Health"],"abstract":"<jats:p>\n                    In school environments, characterized by high occupancy and prolonged exposure, airborne contaminants pose risks to respiratory health and learning outcomes. Portable air cleaners (PACs) are increasingly considered as a supplement to ventilation, yet field-based evidence remains heterogeneous, with few randomized trials and limited data on microbial agents. Here, we describe the design and methodology of a large-scale cluster-randomized controlled trial evaluating PAC effectiveness in Dutch primary school classrooms. The study included 180 classrooms across 29 primary schools, with classrooms clustered within schools and randomized to HEPA-filter PACs, ionization\/plasma PACs, or no PACs. The design incorporated a three-week baseline or two-week post-intervention control period, and three repeated three-week intervention periods in the main phase, totaling up to 14\u202fweeks per school. PACs were pre-tested under standardized laboratory conditions, screened for safety, and operated at comparable clean air delivery rates (CADR). Airborne dust was collected using electrostatic dust fall collectors (EDCs) and analyzed for bacterial markers representing common human microbiome constituents, a general bacterial indicator, and viral markers for seasonal infections. In 12 classrooms, active air sampling was conducted alongside EDCs to validate and quantify passive measurements. Continuous monitoring of particulate matter (PM\u2081\u2080, PM\u2084, PM\u2082.\u2085, PM\u2081), CO\u2082, air temperature, relative humidity, and volatile organic compounds (VOCs) was performed. Classroom-level absenteeism and parent-reported respiratory symptoms were collected retrospectively. Weekly national infectious-disease surveillance and outdoor PM and NO\u2082 data will contextualize indoor measurements and health outcomes. Hierarchical mixed-effects models accounting for school, cluster, and classroom structure will analyze microbial outcomes. Bayesian hierarchical models may be applied for values outside the quantifiable range. By integrating comprehensive indoor air quality assessment with a dual-control design distinguishing pre-existing classroom differences from temporal trends, this registered trial (\n                    <jats:uri>ClinicalTrials.gov<\/jats:uri>\n                    , NCT07479420; 6 March 2026) provides a rigorous framework to evaluate PACs under real-world classroom conditions and support evidence-informed strategies to improve classroom indoor air quality.\n                  <\/jats:p>\n                  <jats:p>\n                    <jats:bold>Clinical trial registration<\/jats:bold>\n                    :\n                    <jats:ext-link>https:\/\/clinicaltrials.gov\/study\/NCT07479420?term=air%20cleaner&amp;amp;viewType=Card&amp;amp;intr=air%20cleaner&amp;amp;rank=4<\/jats:ext-link>\n                    , ClinicalTrials.gov, NCT07479420.\n                  <\/jats:p>","DOI":"10.3389\/fpubh.2026.1892902","type":"journal-article","created":{"date-parts":[[2026,8,25]],"date-time":"2026-08-25T05:34:44Z","timestamp":1787636084000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Evaluating air cleaner effectiveness in schools: a comprehensive review and protocol of a cluster-randomized controlled trial of physicochemical and microbial markers"],"prefix":"10.3389","volume":"14","author":[{"given":"Esm\u00e9e Rianne","family":"Janssen","sequence":"first","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kimberly J.","family":"Linde","sequence":"additional","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marcel G. L. C.","family":"Loomans","sequence":"additional","affiliation":[{"name":"Department of the Built Environment, Eindhoven University of Technology","place":["Eindhoven, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wietske","family":"Dohmen","sequence":"additional","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"L\u00fctzen","family":"Portengen","sequence":"additional","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lili","family":"Xia","sequence":"additional","affiliation":[{"name":"Department of the Built Environment, Eindhoven University of Technology","place":["Eindhoven, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jan F. L.","family":"Diepens","sequence":"additional","affiliation":[{"name":"Department of the Built Environment, Eindhoven University of Technology","place":["Eindhoven, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Dick J. J.","family":"Heederik","sequence":"additional","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Twan","family":"van Hooff","sequence":"additional","affiliation":[{"name":"Department of the Built Environment, Eindhoven University of Technology","place":["Eindhoven, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Inge M.","family":"Wouters","sequence":"additional","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lidwien A. M.","family":"Smit","sequence":"additional","affiliation":[{"name":"Institute for Risk Assessment Sciences, Utrecht University","place":["Utrecht, Netherlands"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,8,25]]},"reference":[{"key":"ref1","doi-asserted-by":"publisher","first-page":"1082","DOI":"10.1017\/S0950268806005875","article-title":"Modelling the transmission of airborne infections in enclosed spaces","volume":"134","author":"Noakes","year":"2006","journal-title":"Epidemiol Infect"},{"key":"ref2","doi-asserted-by":"publisher","first-page":"119","DOI":"10.12932\/AP0838","article-title":"Association of indoor air quality and preschool children\u2019s respiratory symptoms","volume":"35","author":"Siwarom","year":"2017","journal-title":"Asian Pac J Allergy Immunol"},{"key":"ref3","first-page":"682","article-title":"Poor air quality in classrooms related to asthma and rhinitis in primary schoolchildren of the French 6 cities study","volume-title":"Thorax","author":"Annesi-Maesano","year":"2012"},{"key":"ref4","doi-asserted-by":"publisher","first-page":"314","DOI":"10.1183\/09031936.00084612","article-title":"Endotoxin levels in homes and classrooms of Dutch school children and respiratory health","volume":"42","author":"Jacobs","year":"2013","journal-title":"Eur Respir J"},{"key":"ref5","doi-asserted-by":"publisher","first-page":"057002","DOI":"10.1289\/EHP3169","article-title":"Association between early life exposure to air pollution and working memory and attention","volume":"127","author":"Rivas","year":"2019","journal-title":"Environ Health Perspect"},{"key":"ref6","doi-asserted-by":"publisher","first-page":"E2128757","DOI":"10.1001\/jamanetworkopen.2021.28757","article-title":"Transmission of SARS-CoV-2 after COVID-19 screening and mitigation measures for primary school children attending School in Li\u00e8ge, Belgium","volume":"4","author":"Meuris","year":"2021","journal-title":"JAMA Netw Open"},{"key":"ref7","doi-asserted-by":"publisher","first-page":"1144","DOI":"10.1126\/science.ade1675","article-title":"COVID-19 and children","volume":"377","author":"Pierce","year":"2022","journal-title":"Science (1979)"},{"key":"ref8","author":"Moscoviz","year":"2022"},{"key":"ref9","doi-asserted-by":"publisher","first-page":"36","DOI":"10.1016\/j.jad.2021.01.020","article-title":"The psychological impact of COVID-19 and restrictive measures in the world","volume":"283","author":"Passavanti","year":"2021","journal-title":"J Affect Disord"},{"key":"ref10","doi-asserted-by":"publisher","first-page":"231","DOI":"10.1186\/s12887-021-02704-1","article-title":"Interviewing children: the impact of the COVID-19 quarantine on children\u2019s perceived psychological distress and changes in routine","volume":"21","author":"Segre","year":"2021","journal-title":"BMC Pediatr"},{"key":"ref11","doi-asserted-by":"publisher","first-page":"400","DOI":"10.1001\/jamapediatrics.2021.5840","article-title":"School closures during social lockdown and mental health, health behaviors, and well-being among children and adolescents during the first COVID-19 wave: a systematic review","volume":"176","author":"Viner","year":"2022","journal-title":"JAMA Pediatr"},{"key":"ref12","volume-title":"Ventilatie in schoolgebouwen","year":"2022"},{"key":"ref13","volume-title":"Bouwbesluit 2025 [Dutch Building Decree 2025]","year":"2025"},{"key":"ref14","volume-title":"GGD-richtlijn medische milieukunde: ventilatie op school en gezondheid","year":"2023"},{"key":"ref15","volume-title":"Opdracht van het Ministerie van Binnenlandse Zaken en Koninkrijksrelaties","year":"2021"},{"key":"ref16","doi-asserted-by":"publisher","first-page":"109922","DOI":"10.1016\/j.buildenv.2022.109922","article-title":"Ventilation and thermal conditions in secondary schools in the Netherlands: effects of COVID-19 pandemic control and prevention measures","volume":"229","author":"Ding","year":"2023","journal-title":"Build Environ"},{"key":"ref17","doi-asserted-by":"publisher","first-page":"538","DOI":"10.1111\/ina.12231","article-title":"Classroom ventilation and indoor air quality-results from the FRESH intervention study","volume":"26","author":"Rosbach","year":"2016","journal-title":"Indoor Air"},{"key":"ref18","volume-title":"WHO Global air Quality Guidelines. 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