Transmission and infection risk of various pathogen-laden expiratory droplets in a coach bus with COVID-19

Sun Yat-Sen University, Zhuhai, China

^* Corresponding author: hangj3@mail.sysu.edu.cn

Abstract

The study about droplet transmission in crowded, poorly ventilated buses and the resulting infection risk(IR) remains rare. Based on a COVID-19 outbreak which the index patient located at bus rear, we performed CFD simulations to study the effect of initial droplet diameters and hourly ventilation rate(ACH) on droplet transmission and IR. The outdoor pressure differential creates the natural ventilation enters from theskylight at bus rear and exits from the front one. With increased ACH, the IR of tracer gas reduced quickly, from 11.1-15.3% under 0.62ACH to 1.3-3.1% under 5.66ACH. Furthermore, the IR of 100μm/50μm droplets was almost independent of ACH as most droplets were deposited due to gravity. Furthermore, 5μm droplets are more widely dispersed than larger droplets, and can spread further with increasing ACH with a low IR(≤0.4%). Unlike general rooms, most droplets are deposited on the route passing through the long-distance bus space(~9.46m). But the tracer gas will not deposit, so the tracer gas can only be used to simulate the fine droplet dispersion process in the long-distance bus. Our research results provide a reference for future research on droplet transmission in the bus environment, and also provide a guidance for epidemic prevention.