Air cleaners and respiratory infections in schools. A modeling study using epidemiological, environmental, and molecular data

Abstract

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Using a multiple-measurement approach, we examined the real-world effectiveness of portable HEPA-air filtration devices (air cleaners) in a school setting.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We collected environmental (CO<jats:sub>2</jats:sub>, 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.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>All 38 students (age 13<jats:italic>−</jats:italic>15 years) participated. With air cleaners, mean particle con-centration decreased by 77% (95% credible interval 63%<jats:italic>−</jats:italic>86%). There were no differences in CO<jats:sub>2</jats:sub>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<jats:italic>−</jats:italic>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.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>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.</jats:p></jats:sec>