Risk of Infection Due to Airborne Virus in Classroom Environments Lacking Mechanical Ventilation

The COVID-19 pandemic highlighted the role of indoor environments on disease transmission. Enclosed spaces where pathogen-laden aerosols accumulate was strongly linked to increased transmission events. Here we employ a surrogate non-pathogenic virus, the bacteriophage phi6, to interrogate aerosol transmission in classroom environments that do not have any natural or mechanical ventilation in order to determine how effectively aerosols facilitate new infections. We find that virus-laden aerosols establish new infections over all distances tested within minutes and that the time of exposure did not change transmission rate. We further find that humidity, but not temperature nor a UV-based disinfection device, significantly impacted transmission rates. Our data suggest that, even without mechanical ventilation, relative humidity remains a highly effective mitigation strategy while UV air treatment did not. Practical Implications Transmission of pathogens through airborne particles is a major source of disease transmission. People now spend much of their time indoors, thus understanding indoor airborne transmission is vital to managing outbreaks. Most classrooms in the U.S. do not have any mechanical ventilation systems and so here, we test airborne transmission of a virus in such classrooms. Infection transmission rates are not greatly impacted by distance, time or even some UV treatment, but are curbed by the amount of moisture in the air.