Quantifying human and environmental viral load relationships amidst mitigation strategies in a controlled chamber with participants having COVID-19

Several studies indicate that COVID-19 is primarily transmitted within indoor spaces. Therefore, environmental characterization of SARS-CoV-2 viral load with respect to human activity, building parameters, and environmental mitigation strategies is critical to combat disease transmission. We recruited 11 participants diagnosed with COVID-19 to individually occupy a controlled chamber and conduct specified physical activities under a range of environmental conditions; we collected human and environmental samples over a period of three days for each participant. Here we show that increased viral load, measured by lower RNA cycle threshold (CT) values, in nasal samples is associated with higher viral loads in environmental aerosols and surfaces captured in both the near field (1.2 m) and far field (3.5 m). At ambient conditions with ~ 0 Air Changes per Hour (ACH), near field measurements showed a higher particulate matter abundance and carbon dioxide (CO2) concentration as compared to far field measurements. We also found that aerosol viral load in far field is correlated with the number of particulates within the range of 1 µm -2.5 µm. Furthermore, increased ventilation and filtration are associated with lower environmental viral loads, and higher relative humidity is associated with lower aerosol viral loads and higher surface viral loads, consistent with an increased rate of particle deposition. Data from near field aerosol trials with high expiratory activities suggest that respiratory particles of smaller sizes (0.3 µm -1 µm) best characterize the variance of near field aerosol viral load. Moreover, our findings indicate that building operation practices such as ventilation, filtration, and humidification substantially reduce the environmental aerosol viral load, and therefore inhalation dose, and should be prioritized to improve building health and safety.