Environmental Effects on Viable Virus Transport and Resuspension in Ventilation Airflow

Abstract

Currently little is known on how SARS-CoV-2 spreads indoors and its infectability. The objective of this study is to gain more knowledge on the effect of environmental factors on the spread and infectivity of virus aerosols in the built environment. Understanding how the virus transmits indoors would allow for early detection and mitigation of viral particles in room sized spaces. Bovine coronavirus (BCoV) was used as virus simulant in laboratory experiments conducted in a controlled humidity cabinet at Biosafety Level 2. An air-jet nebulizer was used to disseminate known numbers of BCoV particles. After aerosolization, the surface in the cabinet was swiped at regular time intervals to assess the number of particles impacted. Additional surfaces placed in the chamber and swiped at the end of testing. The samples were quantified using quantitative polymerase chain reaction (qPCR). Virus attachment to the surfaces was analyzed using bio-layer interferometry. The virus aerosols that remained suspended in the air were collected bioaerosol collectors with a reference air sampler and quantitated by qPCR. To monitor the effect of the ventilation on the virus movement, PRD1 bacteriophage aerosols as virus simulants were also disseminated in a ¾ scale ventilated hospital test room equipped with twelve PM2.5 samplers at 15 L/min. After plating and counting the plaque forming units (PFU), the highest concentration of viral particles was detected above the patient’s head in the test room in the second ventilation configuration. Other high virus concentration locations were near the foot of the patient’s bed. From these results, it was determined that with the current airflow set up in the second configuration with the air inlet on the ceiling above the bed, exhaust bottom left on the wall behind the bed, the virus particles concentrate over the lower part of the patient’s bed. Based on air property measurements, aerosol collections and the mechanical blueprint of the model room, a computational flow model was created to visualize the entrainment and movement of the virus in the ventilation airflow. The models showed the third presented configuration minimized particle concentration at the door while the first configuration decreased overall particle concentration in the room.