Air Cleaners and Respiratory Infections in Schools: A Modeling Study Based on Epidemiologic, Environmental, and Molecular Data

Nicolas Banholzer; Philipp Jent; Pascal Bittel; Kathrin Zürcher; Lavinia Furrer; Simon Bertschinger; Ernest Weingartner; Alban Ramette; Matthias Egger; Tina Hascher; Lukas Fenner

doi:10.1093/ofid/ofae169

Air Cleaners and Respiratory Infections in Schools: A Modeling Study Based on Epidemiologic, Environmental, and Molecular Data

Open Forum Infect Dis. 2024 Mar 21;11(4):ofae169. doi: 10.1093/ofid/ofae169. eCollection 2024 Apr.

Authors

Nicolas Banholzer^{1

2}, Philipp Jent^{2

3}, Pascal Bittel^{2

4}, Kathrin Zürcher^{1

2}, Lavinia Furrer⁴, Simon Bertschinger¹, Ernest Weingartner⁵, Alban Ramette^{2

4}, Matthias Egger^{1

6

7}, Tina Hascher^{2

8}, Lukas Fenner^{1

2}

Affiliations

¹ Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
² Multidisciplinary Center for Infectious Diseases, University of Bern, Bern, Switzerland.
³ Department of Infectious Diseases, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
⁴ Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
⁵ Institute for Sensors and Electronics, University of Applied Sciences and Arts Northwestern Switzerland, Windisch, Switzerland.
⁶ Population Health Sciences, University of Bristol, Bristol, UK.
⁷ Centre for Infectious Disease Epidemiology and Research, University of Cape Town, Cape Town, South Africa.
⁸ Institute of Educational Science, University of Bern, Bern, Switzerland.

Abstract

Background: 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 data over 7 weeks during winter 2022/2023 in 2 Swiss secondary school classes: environmental (CO₂, particle concentrations), epidemiologic (absences related to respiratory 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 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%), 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 respiratory 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.