Banholzer, NicolasNicolasBanholzerJent, PhilippPhilippJentBittel, PascalPascalBittelZürcher, KathrinKathrinZürcherFurrer, LaviniaLaviniaFurrerBertschinger, Simon MichaelSimon MichaelBertschingerWeingartner, ErnestErnestWeingartnerRamette, Alban NicolasAlban NicolasRamette0000-0002-3437-4639Egger, MatthiasMatthiasEgger0000-0001-7462-5132Hascher, TinaTinaHascherFenner, Lukas AntoineLukas AntoineFenner0000-0003-3309-48352024-10-262024-10-262023-12-30https://boris-portal.unibe.ch/handle/20.500.12422/173683BACKGROUND Using a multiple-measurement approach, we examined the real-world effectiveness of portable HEPA-air filtration devices (air cleaners) in a school setting. METHODS We collected environmental (CO2, particle concentrations), epidemiological (absences related to respiratory infections), audio (coughing), and molecular data (bioaerosol and saliva samples) over seven weeks during winter 2022/2023 in two Swiss secondary school classes. Using a cross-over study design, we compared particle concentrations, coughing, and the risk of infection with vs without air cleaners. RESULTS All 38 students (age 13-15 years) participated. With air cleaners, mean particle concentration decreased by 77% (95% credible interval 63%-86%). There were no differences in CO2 levels. Absences related to respiratory infections were 22 without vs 13 with air cleaners. Bayesian modeling suggested a reduced risk of infection, with a posterior probability of 91% and a relative risk of 0.73 (95% credible interval 0.44-1.18). Coughing also tended to be less frequent (posterior probability 93%). Molecular analysis detected mainly non-SARS-CoV-2 viruses in saliva (50/448 positive), but not in bioaerosols (2/105 positive) or HEPA-filters (4/160). The detection rate was similar with vs without air cleaners. Spatiotemporal analysis of positive saliva samples identified several likely transmissions. CONCLUSIONS Air cleaners improved air quality, showed a potential benefit in reducing respiratory infections, and were associated with less coughing. Airborne detection of non-SARS-CoV-2 viruses was rare, suggesting that these viruses may be more difficult to detect in the air. Future studies should examine the importance of close contact and long-range transmission, and the cost-effectiveness of using air cleaners.enair cleaner airborne transmission molecular detection respiratory viruses schools600 - Technology::610 - Medicine & health300 - Social sciences, sociology & anthropology::360 - Social problems & social services300 - Social sciences, sociology & anthropology::370 - Education500 - Science::570 - Life sciences; biologyworking_paper10.48350/1919863823472310.1101/2023.12.29.23300635