During respiratory virus outbreaks, mobile air cleaning devices (MACs) are increasingly considered in schools as a preventive measure. However, evidence on their real-world performance, feasibility, and potential health impact in classroom settings remains limited. This pilot study was conducted to inform the design of a future large-scale trial by providing a comprehensive evaluation of MACs in primary school classrooms, integrating technical performance (including indoor air quality and airborne microbial assessments), user-perceived feasibility, and the suitability of illness-related absenteeism as a potential pragmatic outcome measure for infection rates. A randomized cross-over study was conducted in five Dutch primary schools, involving 45 classrooms equipped with MACs. Each classroom alternated between three-week periods with the devices switched on and off. Indoor air quality was assessed in a subset of classrooms using sensors for CO₂ and particulate matter, while airborne microbial contamination was monitored through air dust sampling and molecular testing. Illness-related absenteeism was evaluated as a potential outcome measure. MACs effectively halved indoor particulate matter levels, confirming their technical performance. This reduction did not translate into a measurable reduction in airborne microbial contamination, although such contamination was successfully detected. Feasibility assessment revealed low acceptability among teachers due to reduced environmental comfort. Absenteeism was identified as a suitable proxy for infectious diseases, with simulations indicating that a future cluster-randomized trial would require 40–70 schools to detect a 20–25% reduction in absenteeism. ... Read more

Mobile air cleaners (MACs) have been proposed as a supplementary solution to combat the spread of respiratory aerosols in school classrooms. To determine which, where and how to use MACs, seven small- and medium-sized MACs were selected and assessed for different settings and configurations by 1) a decay test for determining the clean air delivery rate (CADR), and 2) a perception test with a panel of subjects, together with physical measurements, of noise and air movement. The findings show that to achieve the desired CADR (appr. 1000 m3/h for 30 students per classroom), the key factors are the induced airflow pattern and the location of the MACs. MACs with an upward air supply toward the occupied zone showed much higher CADR (max. 775–1332 m3/h) than those with a horizontal air supply (max. 219–333 m3/h). Moreover, using multiple devices simultaneously was crucial when the room size was increased, and combining mechanical ventilation could improve aerosol removal. Achieving a sufficient CADR would always lead to a noise level above the limit of 35 dB(A), yet sometimes the rating of the panel was more than 50% acceptable. The air velocities mostly fulfilled the requirement (<0.2 m/s), which aligned with the positive panel assessment. Hence, the evaluation by a panel of subjects can help to optimize the use of MACs in a classroom. ... Read more