Airborne MicroorganismsCLAIRENCT07479420
Clean Air for Everyone (CLAIRE): an Intervention Study to Reduce the Amount of Fine Particulate Matter and Microorganisms in Classroom Air
A study testing HEPA filter air cleaners and Ionization or plasma air cleaners in people with Airborne Microorganisms and Particulate Matter (PM), run by Lidwien Smit at 1 site in Netherlands.
Trial summary
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. Read more about this study
- Who is it for?
- Ages 5 to 13 yearsHealthy volunteers can take part
- Conditions the study is for
- Airborne Microorganisms, Particulate Matter (PM)
- What is being tested?
- HEPA filter air cleaners and Ionization or plasma air cleaners
- Type of treatment
- Medical device
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 180 participants
- Where
- 1 siteNetherlands
- Study dates
- 6 Dec 2023to 1 May 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 5 to 13 years
- All sexes
- Healthy volunteers accepted
- Child
Who may be able to join
- 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
Who cannot join
- 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
Trial locations and contacts
1 site in 1 country.
About this study
Official title: Cluster-randomized Controlled Trial Assessing the Impact of Air Cleaning Technologies on Microbial and Physicochemical Markers in Primary School Classrooms
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.
Read the detailed description
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.
- Conditions
- Airborne Microorganisms, Particulate Matter (PM)
- Being tested
- HEPA filter air cleaners, Ionization or plasma air cleaners
- Keywords
- Air cleaner, Indoor air quality, Primary schools, Particulate matter, Respiratory viruses, Airborne bacteria, Cluster-randomized trial
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
HEPA filter air cleanersDevice
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 cleanersDevice
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.
| Study group | Role | What they receive |
|---|---|---|
| HEPA filter air cleaners | Experimental | Classrooms received a portable HEPA filter air cleaner, operated for the duration of the study. Receives: Device: HEPA filter air cleaners |
| Ionization or plasma air cleaners | Experimental | Classrooms received a portable ionization or plasma air cleaners, operated for the duration of the study. Receives: Device: Ionization or plasma air cleaners |
| Control | No intervention | Classrooms received no intervention. |
What is being measured
The primary outcome is the main question the study is designed to answer.
Presence and/or concentration of airborne bacteria and viruses in classroom air
Measured: 12 weeks per school
Concentration of particulate matter in classroom air
Measured: 11 weeks per school
Secondary outcomes (2)
Respiratory symptoms
Number of participants with reported respiratory symptoms. Assessed using parent-reported questionnaires covering the study period.
Measured: Up to 12 months
Student absentee data
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.
Measured: 12 weeks per school
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted18 Mar 2026
- Study start6 Dec 2023
- Primary completion1 May 2025
- Study completion1 May 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (3)Papers the sponsor has linked to this study.
- Other trials for Airborne MicroorganismsStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Cluster-randomized controlled trial in primary school classrooms. Classrooms were randomly assigned to one of two air cleaning interventions or a control condition. All classrooms had a baseline period prior to intervention and repeated measurements.
- Masking
- Single blind
- Who is masked
- Outcomes assessor
- Enrolment
- 180 participants (actual)
Sponsor and investigators
- Lead sponsor
- Lidwien Smit
- Sponsor type
- University, hospital or other
- Collaborators
- Utrecht University, Eindhoven University of Technology
- Responsible party
- Sponsor-investigator, Lidwien Smit, Utrecht University
- Investigators
- Lidwien A. Smit, PhD, Principal investigator, Utrecht University
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07479420
- Sponsor's protocol ID
- 10031209
- Other IDs
- LSHM22032
- Acronym
- CLAIRE
- Status last verified
- Mar 2026
- First submitted
- 6 Mar 2026
- Last updated
- 18 Mar 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided
Publications
Noss I, Wouters IM, Visser M, Heederik DJ, Thorne PS, Brunekreef B, Doekes G. Evaluation of a low-cost electrostatic dust fall collector for indoor air endotoxin exposure assessment. Appl Environ Microbiol. 2008 Sep;74(18):5621-7. doi: 10.1128/AEM.00619-08. Epub 2008 Aug 1.
PubMed 18676704ANSI/AHAM. AC-1-2020: Method for Measuring Performance of Portable Household Electric Room Air Cleaners. 2020.
Janssen ER, Linde KJ, Loomans MGLC, Dohmen W, Portengen L, Xia L, Diepens JFL, Heederik DJJ, van Hooff T, Wouters IM, Smit LAM. Evaluating air cleaner effectiveness in schools: a comprehensive review and protocol of a cluster-randomized controlled trial of physicochemical and microbial markers. Front Public Health. 2026 Aug 25;14:1892902. doi: 10.3389/fpubh.2026.1892902. eCollection 2026.
PubMed 42712555
Study at a glance
From the registry record, last updated by the sponsor on 18 Mar 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Cluster-randomized Controlled Trial Assessing the Impact of Air Cleaning Technologies on Microbial and Physicochemical Markers in Primary School Classrooms
- ClinicalTrials.gov ID
- NCT07479420
- Acronym / sponsor ID
- CLAIRE / 10031209
- Conditions
- Airborne Microorganisms, Particulate Matter (PM)
- Keywords
- Air cleaner, Indoor air quality, Primary schools, Particulate matter, Respiratory viruses, Airborne bacteria, Cluster-randomized trial
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 180 participants (actual)
- Lead sponsor
- Lidwien SmitUniversity, hospital or other
- Collaborators
- Utrecht University, Eindhoven University of Technology
- Study start
- 6 Dec 2023 (actual)
- Primary completion
- 1 May 2025 (actual)
- Study completion
- 1 May 2025 (actual)
- First posted
- 18 Mar 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Detailed description
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.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Single blind (outcomes assessor)
- Number of arms
- 3
- Model description
- Cluster-randomized controlled trial in primary school classrooms. Classrooms were randomly assigned to one of two air cleaning interventions or a control condition. All classrooms had a baseline period prior to intervention and repeated measurements.
| Arm | Type | Receives |
|---|---|---|
| HEPA filter air cleaners | Experimental | Device: HEPA filter air cleanersClassrooms received a portable HEPA filter air cleaner, operated for the duration of the study. |
| Ionization or plasma air cleaners | Experimental | Device: Ionization or plasma air cleanersClassrooms received a portable ionization or plasma air cleaners, operated for the duration of the study. |
| Control | No intervention | –Classrooms received no intervention. |
Who may qualify
- Ages
- 5 to 13 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Child
Key inclusion criteria (3 listed)
- 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
Key exclusion criteria (4 listed)
- 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
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| HEPA filter air cleanersClassrooms 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. | Device | HEPA filter air cleaners |
| Ionization or plasma air cleanersClassrooms 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. | Device | Ionization or plasma air cleaners |
Primary outcome
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
2 secondary outcomes
Respiratory symptoms
Time frame: Up to 12 months
Student absentee data
Time frame: 12 weeks per school
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 18 Mar 2026.
- Results publication: PubMed 18676704Noss I, Wouters IM, Visser M, Heederik DJ, Thorne PS, Brunekreef B, Doekes G. Evaluation of a low-cost electrostatic dust fall collector for indoor air endotoxin exposure assessment. Appl Environ Microbiol. 2008 Sep;74(18):5621-7. doi: 10.1128/AEM.00619-08. Epub 2008 Aug 1.
- Results publicationANSI/AHAM. AC-1-2020: Method for Measuring Performance of Portable Household Electric Room Air Cleaners. 2020.
- Derived from this study: PubMed 42712555Janssen ER, Linde KJ, Loomans MGLC, Dohmen W, Portengen L, Xia L, Diepens JFL, Heederik DJJ, van Hooff T, Wouters IM, Smit LAM. Evaluating air cleaner effectiveness in schools: a comprehensive review and protocol of a cluster-randomized controlled trial of physicochemical and microbial markers. Front Public Health. 2026 Aug 25;14:1892902. doi: 10.3389/fpubh.2026.1892902. eCollection 2026.
- Individual participant dataSharing planned: Undecided
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Lidwien A. Smit, PhD principal investigator
Utrecht University
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing HEPA filter air cleaners and Ionization or plasma air cleaners in people with Airborne Microorganisms and Particulate Matter (PM), run by Lidwien Smit at 1 site in Netherlands.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 3 inclusion and 4 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 18 Mar 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Netherlands. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Presence and/or concentration of airborne bacteria and viruses in classroom air (time frame: 12 weeks per school). The study lists 2 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07479420, which also lists 3 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 18 Mar 2026; AzTrials last refreshed its copy on 4 Nov 2026.