Completed

NCT Number: NCT07479420

Clean Air for Everyone (CLAIRE): an Intervention Study to Reduce the Amount of Fine Particulate Matter and Microorganisms in Classroom Air

In this study, the investigators tested whether portable air cleaners can improve the air quality in primary school classrooms. Poor air quality can affect children's respiratory health and learning. Classroom air quality is a key concern, as children spend a large part of their day there, often with many students in one room. The investigators studied air quality in 180 classrooms in 29 Dutch primary schools. Within each school, classrooms were grouped in threes based on similar characteristics, such as size, number of students, and ventilation system. Classrooms in each group were randomly assigned to receive either: an air cleaner with a filter that traps particles from the air, an air cleaner that uses an electric charge to remove particles from the air, or no air cleaner (control). All devices were tested for safety in a laboratory beforehand. Measurements were taken in all classrooms before the devices were switched on, to provide a refence point. The air cleaners were then operated for nine weeks. After that, air cleaners were switched off for two weeks while additional measurements continued. To measure the effect of air cleaners, special cloths were placed in classrooms to collect dust and tiny droplets from the air, which were later analyzed in a laboratory for bacteria and viruses. This included viruses that commonly cause respiratory infections, such as flu and respiratory syncytial virus (RSV), and bacteria originating from the human skin, nose, or mouth that can spread through the air. Small sensors also tracked tiny particles in the air (particulate matter). The investigators collected additional information on classroom attendance and parent-reported respiratory symptoms to explore possible links. This study provides real-world evidence on how portable air cleaners can affect classroom air quality and may help guide decisions to improve indoor air environments in schools.

Completed

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Key information

Conditions

Airborne Microorganisms Particulate Matter (PM)

Age range

5 year–13 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Utrecht University

Utrecht, 3508 TC, Netherlands

About this study

The cluster-randomized trial evaluated the effectiveness of portable air cleaners in 180 classrooms across 29 Dutch primary schools. Classrooms were grouped within schools based on similar characteristics and randomly assigned to receive either HEPA-filter air cleaners, ionization/plasma air cleaners, or no air cleaners. The study contained a three-week baseline, followed by three repeated three-week intervention periods and a two-week post-intervention period, resulting in 14 weeks of measurements per school. Air cleaners were pre-tested for safety and operated at a clean air delivery rate (CADR) of approximately 400-500 m³/h during intervention. Airborne dust was collected using electrostatic dust fall collectors (EDCs), a passive air sampling method, and analyzed for respiratory viruses, human-associated bacteria and a general bacterial marker using quantitative polymerase chain reaction (qPCR). In a subset of eleven classrooms, active air sampling was performed alongside EDCs, to validate and quantify passive measurements. Low-cost indoor air sensors continuously monitored particulate matter, CO₂, temperature, relative humidity, and volatile organic compounds (VOCs). Retrospective parent-reported respiratory symptoms and classroom absenteeism data were gathered by surveys. Outcomes will be analyzed using hierarchical mixed-effects models.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

Primary schools with at least three comparable classrooms between grade 3-8
Regular primary education classrooms
Primary schools located within reasonable travel distance of Utrecht, the Netherlands

Exclusion criteria

Schools for special education
Secondary schools
Kindergarten classes (grade 1&2; approximately ages 4-6 years)
Schools unable or unwilling to provide the required study information

Treatment and study plan

HEPA filter air cleaners

Device

Classrooms received a portable HEPA filter air cleaner, operated for the duration of the study. Devices were set to provide an approximate clean air delivery rate (CADR) of 400-500 m³/h. Maintenance was performed according to manufacturer guidelines.

Ionization or plasma air cleaners

Device

Classrooms received an ionization or plasma air cleaners, operated for the duration of the study. Devices were set to provide an approximate clean air delivery rate (CADR) of 400-500 m³/h. Maintenance was performed according to manufacturer guidelines.

Primary outcomes

Presence and/or concentration of airborne bacteria and viruses in classroom air

Time frame: 12 weeks per school
Concentration of particulate matter in classroom air

Time frame: 11 weeks per school

Secondary outcomes

Respiratory symptoms

Time frame: Up to 12 months

Number of participants with reported respiratory symptoms. Assessed using parent-reported questionnaires covering the study period.
Student absentee data

Time frame: 12 weeks per school

Student absence from school (yes or no). Anonymous student absentee data were collected from school records after the intervention period. The outcome reflects absenteeism during the period when air cleaning interventions were applied in the classrooms.

Sponsors and collaborators

Lead sponsor

Lidwien Smit

Other

Collaborators

Eindhoven University of Technology
Utrecht University

Registry information

Official study title

Cluster-randomized Controlled Trial Assessing the Impact of Air Cleaning Technologies on Microbial and Physicochemical Markers in Primary School Classrooms

Acronym: CLAIRE

Important dates

Study start: 2023
Primary completion: 2025
Study completion: 2025
First posted: Mar 18, 2026
Registry last updated: Mar 18, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.