Insufficient ventilation led to a probable long-range airborne transmission of SARS-CoV-2 on two buses

Cuiyun Ou; Shixiong Hu; Kaiwei Luo; Hongyu Yang; Jian Hang; Pan Cheng; Zheng Hai; Shanliang Xiao; Hua Qian; Shenglan Xiao; Xinping Jing; Zhengshen Xie; Hong Ling; Li Liu; Lidong Gao; Qihong Deng; Benjamin J Cowling; Yuguo Li

doi:10.1016/j.buildenv.2021.108414

Insufficient ventilation led to a probable long-range airborne transmission of SARS-CoV-2 on two buses

Build Environ. 2022 Jan:207:108414. doi: 10.1016/j.buildenv.2021.108414. Epub 2021 Oct 2.

Authors

Cuiyun Ou¹, Shixiong Hu², Kaiwei Luo², Hongyu Yang¹, Jian Hang¹, Pan Cheng³, Zheng Hai⁴, Shanliang Xiao⁵, Hua Qian⁶, Shenglan Xiao³, Xinping Jing⁴, Zhengshen Xie⁴, Hong Ling¹, Li Liu⁷, Lidong Gao², Qihong Deng⁸, Benjamin J Cowling⁹, Yuguo Li^{3

9}

Affiliations

¹ School of Atmospheric Sciences, Sun Yat-sen University, and Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China.
² Hunan Provincial Center for Disease Control and Prevention, Changsha, China.
³ Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, China.
⁴ Shaodong County Center for Disease Control and Prevention, Shaodong, China.
⁵ Shaoyang City Center for Disease Control and Prevention, Shaoyang, China.
⁶ School of Energy and Environment, Southeast University, Nanjing, China.
⁷ School of Architecture, Tsinghua University, Beijing, China.
⁸ XiangYa School of Public Health, Central South University, Changsha, China.
⁹ School of Public Health, The University of Hong Kong, Hong Kong, China.

Abstract

Uncertainty remains on the threshold of ventilation rate in airborne transmission of SARS-CoV-2. We analyzed a COVID-19 outbreak in January 2020 in Hunan Province, China, involving an infected 24-year-old man, Mr. X, taking two subsequent buses, B1 and B2, in the same afternoon. We investigated the possibility of airborne transmission and the ventilation conditions for its occurrence. The ventilation rates on the buses were measured using a tracer-concentration decay method with the original driver on the original route. We measured and calculated the spread of the exhaled virus-laden droplet tracer from the suspected index case. Ten additional passengers were found to be infected, with seven of them (including one asymptomatic) on B1 and two on B2 when Mr. X was present, and one passenger infected on the subsequent B1 trip. B1 and B2 had time-averaged ventilation rates of approximately 1.7 and 3.2 L/s per person, respectively. The difference in ventilation rates and exposure time could explain why B1 had a higher attack rate than B2. Airborne transmission due to poor ventilation below 3.2 L/s played a role in this two-bus outbreak of COVID-19.

Keywords: Airborne transmission; COVID-19; Public transport; SARS-CoV-2 infection; Ventilation requirement.