Air cleaners and respiratory infections in schools: a modeling study based on epidemiologic, environmental, and molecular data

Abstract

Background. Using a multiple-measurement approach, we examined the real-world effective-ness of portable HEPA air filtration devices (air cleaners) in a school setting. Methods. We collected data over 7 weeks during winter 2022/2023 in 2 Swiss secondary school classes: environmental (CO2, particle concentrations), epidemiologic (absences related to res-piratory infections), audio (coughing), and molecular (bioaerosol and saliva samples). Using a crossover design, we compared particle concentrations, coughing, and risk of infection with and without air cleaners. Results. All 38 students participated (age, 13–15 years). 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 air cleaners vs 13 with them. Bayesian modeling suggested a reduced risk of infection, with a pos-terior 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%), indicating that fewer symptomatic students were in class. Molecular analysis detected mainly non–SARS-CoV-2 viruses in saliva (50/448 positive) but not in bioaerosols (2/105) or on the HEPA filters of the air cleaners (4/160). The molecular detection rate in saliva was similar with and without air cleaners. Spatiotemporal analysis of positive saliva samples identified several likely transmissions. Conclusions. Air cleaners improved air quality and showed potential benefits in reducing respira-tory infections. 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. Keywords. air cleaner; airborne transmission; molecular detection; respiratory viruses; schools.