Investigation of air change rate and aerosol behavior during an outbreak of COVID-19 in a geriatric care facility

Abstract

We investigated the air change rate (ACR) using the tracer gas method in five areas where the risk of aerosol infection was assumed to be high for an outbreak of an infection among 59 people in a nursing home in Miyagi Prefecture, Japan. The ACRs at the time of the outbreak were estimated to be 4.35, 2.42, 2.04, 4.96, and 6.26 per hour in the general bathroom, special bathroom, shared room, private room, and day room, respectively. In general bathrooms, special bathrooms, shared rooms, and private rooms, the ACR greatly increased by 1.48-5.74 times by opening windows. Because the private rooms, where the initial infected patients were thought to have been, were spatially connected to the common recreational day room, the transfer of aerosols from private rooms to the day room may have been the origin of the mass infection. We reproduced the downwind contamination situation using thermo-fluid simulations and found that infectious aerosols could reach the day room in approximately one minute through the corridor. In elderly care facilities, open architectural spaces are advocated to realize a Quality of Life (QoL) and monitor residents; however, management is required to reduce the downwind infection risk from aerosols and ACR.