Airborne transmission of the Delta variant of SARS-CoV-2 in an auditorium. (1st July 2022)

• Record Type: Journal Article
• Authors: Huang, Jianxiang; Hao, Tongping; Liu, Xiao; Jones, Phil; Ou, Cuiyun; Liang, Weihui; Liu, Fuqiang
• Is Part Of: Building and environment. Volume 219(2022)
• Publication Date: 2022-07-01
• Subjects: COVID-19 -- Delta variant -- Airborne transmission -- Numerical simulation -- Auditorium; Buildings -- Environmental engineering -- Periodicals; Building -- Research -- Periodicals; Constructions -- Technique de l'environnement -- Périodiques; Electronic journals; 696
• DOI: 10.1016/j.buildenv.2022.109212
• Languages: English
• ISSNs: 0360-1323

Abstract

Abstract: The Delta variant of SARS-CoV-2 has inflicted heavy burdens on healthcare systems globally, although direct evidence on the quantity of exhaled viral shedding from Delta cases is lacking. The literature remains inconclusive on whether existing public health guidance, based on earlier evidence of COVID-19, should respond differently to more infectious viral strains. This paper describes a study on an outbreak of the Delta variant of COVID-19 in an auditorium, where one person contracted the virus from three asymptomatic index cases sitting in a different row. Field inspections were conducted on the configuration of seating, building and ventilation systems. Numerical simulation was conducted to retrospectively assess the exhaled viral emission, decay, airborne dispersion, with a modified Wells-Riley equation used to calculate the inhalation exposure and disease infection risks at the seat level. Results support the airborne disease transmission. The viral emission rate for Delta cases was estimated at 31 quanta per hour, 30 times higher than those of the original variant. The high quantity of viral plume exhaled by delta cases can create a high risk zone nearby, which, for a mixing ventilation system, cannot be easily mitigated by raising mixing rates or introducing fresh air supply. Such risks can be reduced by wearing an N95 respirator, less so for social distancing. A displacement ventilation system, through which the air is supplied at the floor and returned from the ceiling, can reduce risks compared with a mixing system. The study has implications for ventilation guidelines and hygiene practices in light of more infectious viral strains of COVID-19. Highlights: An outbreak of the Delta variant of COVID-19 in a mechanically ventilated auditorium was studied. The viral emission rates from Delta cases were 30 times higher than those of the original lineage. The more contagious viral variant cannot be mitigated by sufficient air ventilation alone. A displacement ventilation system provides additional protections than a mixing system. N95 masks are effective against more contagious viral variants, less so for social distancing.