Integrating CFD and exposure modeling for estimating viral exposures at the air-surface interface

Integration of CFD modeling with exposure models for exploring relationships between surface and air transmission routes provides insights into how indoor design and engineering controls influence exposures. One environment in which this integrated methodology is being used is in healthcare. The study objective was to evaluate the influences of differences in healthcare professionals’ (HCPs’) behavior and differences in deposition of norovirus-containing bioaerosols on surfaces for different single patient room layouts and air exchange rates on norovirus accruement on HCP hands. A finite volume Navier Stokes computational fluid dynamics (CFD) model using Lagrangian particle tracking was integrated with a calibrated microbial transfer model and a human behavior model informed by observed mock doctors’ rounds. Viral accruement on hands was estimated for two single patient room set ups, or “room orientations,” where the patient was facing the right side of the room (right-facing) or the left (left-facing). Three air changes per hour (ACH) (10, 6, and 2.5 ACH) and three inlet/outlet scenarios were explored. Viral accruement was compared by room orientation, ACH, and inlet/outlet scenario. The most influential surface on viral accruement on hands was the patient. Greater deposition on the patient occurred when the windows acted as velocity inlets and the door as a pressure outlet (for all 3 ACHs) or when the small windows were velocity inlets and the large window was a pressure outlet (for 6 and 2.5 ACH). When deposition on the patient was different between left- and right-facing rooms, deposition differences drove differences in accruement on hands as opposed to differences in observed behaviors between left- and right-facing rooms. Further modeling expansions include incorporating dose-related behaviours (e.g., self-inoculation), to allow for risk assessment applications.