Airborne infection risk assessment of COVID-19 in an inpatient department through on-site occupant behavior surveys

Abstract

Airborne transmission is a possible infection route of the coronavirus disease 2019 (COVID-19). This investigation focuses on the airborne infection risk of COVID-19 in a nursing unit in an inpatient building in Shenzhen, China. On-site measurements and questionnaire surveys were conducted to obtain the air change rates and occupant trajectories, respectively. The aerosol transport and dose-response models were applied to evaluate the infection risk. The average outdoor air change rate measured in the wards was 1.1 h^-1, which is below the minimum limit of 2.0 h^-1 required by ASHRAE 170-2021. Considering the surveyed occupant behavior during one week, the patients and their attendants spent an average of 19.4 h/d and 15.1 h/d, respectively, in the wards, whereas the nurses primarily worked in the nurse station (3.0 h/d) and wards (2.4 h/d). The doctors primarily worked in their offices (2.6 h/d) and wards (1.1 h/d). Assuming one undetected COVID-19 infector emitting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the nursing unit, we calculated the accumulated viral dose and infection probabilities of the occupants. After one week, the cumulative infection risks of the patients and attendants were almost equal (0.002), and were higher than those of the nurses (0.0013) and doctors (0.0004). Proper protection measures, such as reducing the number of attendants, increasing the air change rate, and wearing masks, were found to reduce the infection risk. It should be noted that the reported results are based on several assumptions, such as the speculated virological properties of SARS-CoV-2 and the particular trajectories of occupants. Moreover, only second generations of transmission were taken into consideration, whereas in reality, the week-long exposure may cause third generation of transmission or worse.

Keywords: COVID-19; Infection risk; Inpatient department; Occupant behavior.

Fig. 1

Nursing unit in a comprehensive hospital in Shenzhen, China: (a) surveyed inpatient building highlighted in orange and (b) plan of the inpatient building. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2

Virus transport via exhaled aerosols in a ward.

Fig. 3

Removal rate for different particle size bins: (a) surface deposition rate; (b) filtration rate; and (c) total removal rate.

Fig. 4

Flowchart of the study methodology.

Fig. 5

Occupancy in different functional spaces: (a) doctors; (b) nurses; (c) patients; and (d) attendants.

Fig. 6

Daily dwell times in different functional spaces: (a) daily-average dwell time; (b) dwell time quartile figure of medical staff; and (c) dwell time quartile figure of the patients and attendants.

Fig. 7

Daily averaged contact duration: (a) cumulative histogram and (b) quartile figure.

Fig. 8

Weekly infection probability: (a) total viral dose in different functional spaces and (b) infection probability of susceptible occupants from different groups.

Fig. 9

Cross-infection probability among all occupant groups in the nursing unit.

Fig. 10

Weekly infection risk in seven scenarios: (a) quartile graph of infection probability and (b) average infection probabilities of different occupant groups.

Fig. 11

Distribution of infection risks for different values of k.