Aerosol transmission of SARS-CoV-2 due to the chimney effect in two high-rise housing drainage stacks

Abstract

Stack aerosols are generated within vertical building drainage stacks during the discharge of wastewater containing feces and exhaled mucus from toilets and washbasins. Fifteen stack aerosol-related outbreaks of coronavirus disease 2019 (COVID-19) in high-rise buildings have been observed in Hong Kong and Guangzhou. Currently, we investigated two such outbreaks of COVID-19 in Hong Kong, identified the probable role of chimney effect-induced airflow in a building drainage system in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We injected tracer gas (SF6) into the drainage stacks via the water closet of the index case and monitored tracer gas concentrations in the bathrooms and along the facades of infected and non-infected flats and in roof vents. The air temperature, humidity, and pressure in vertical stacks were also monitored. The measured tracer gas distribution agreed with the observed distribution of the infected cases. Phylogenetic analysis of the SARS-CoV-2 genome sequences demonstrated clonal spread from a point source in cases along the same vertical column. The stack air pressure and temperature distributions suggested that stack aerosols can spread to indoors through pipe leaks which provide direct evidence for the long-range aerosol transmission of SARS-CoV-2 through drainage pipes via the chimney effect.

Vertical outbreak of COVID-19 in high-rise buildings: The role of sewer stacks and prevention measures

“…The vertical outbreak came into the spotlight as a serious SARS (Severe Acute Respiratory Syndrome) outbreak happened back in 2003 at a private residential apartment in Hong Kong, resulting in 42 deaths and 321 infected cases [ 34 ]. For the current COVID-19 pandemic, 15 vertical outbreaks in residential buildings were reported in Hong Kong and Guangzhou, China [ 35 , 36 ], and one outbreak in Seoul, South Korea [ 37 ] ( Table 1 ). The infected cases were detected along the vertical line in the buildings connected by the same plumbing pipe.…”

A review of facilities management interventions to mitigate respiratory infections in existing buildings

“…Six publications in this review confirmed that viral aerosols in Amoy Gardens' building plumbing were sucked into unit bathrooms through floor drains, contributing significantly to the outbreak, with case studies [ 110 , 113 ], experimental studies [ 107 ], and simulations [ 108 , 111 , 112 ]. Unsurprisingly, another study cluster emerged during the Covid-19 pandemic, employing similar research approaches, such as case studies [ 117 ], experiments [ 115 , 116 ], and modelling [ 109 , 114 , 118 ]. However, the settings of SARS drainage studies were all high-rise Multi-Unit Residential Buildings (MURB), while Covid-19 studies extended the research on hospitals and general high-rise buildings.…”

“…As a result, the drainage system intervention's primary objective was to operate and maintain the existing drainage facilities properly: (1) Regular inspection: FM team is recommended to regularly inspect or deploy a defective trap identification system [ 108 ] to monitor water seal [ 114 ], such as sanitary fixtures equipped with U-traps [ 113 ]. Moreover, it is critical to control tenant installations of equipment that might cause drain lines to get clogged, resulting in pipeline congestion [ 115 ]. (2) Repair and maintenance: The case study by Wong et al highlighted the challenge of maintaining sewage systems in hospitals during the Covid-19 pandemic and the importance of accurately mapping the sewage pipework, especially in older architectures, for rapid response to pipe leakage [ 117 ].…”

Simulation Studies Provide Evidence of Aerosol Transmission of SARS-CoV-2 in a Multi-Story Building via Air Supply, Exhaust and Sanitary Pipelines

“…In an outbreak of COVID-19 in vertically aligned flats in a high-rise building, Kang et al used ethane tracer gas in the bathroom for airflow and dispersion tests and clarified the importance of U-shaped water traps and bathroom ventilation [3]. In two housing blocks in Hong Kong, Wang et al used SF6 tracer gas to conduct toilet simulation experiments and believed that SARS-CoV-2 could be transmitted by long-range aerosol through drainage pipes [19]. Li et al adopted computational fluid dynamics to model the trajectories of aerosol particles during toilet flushing and observed massive upward transport of virus particles [13].…”

“…During quarantine, the early quarantined persons on the fifth floor and the late quarantined person in the non-vertically adjacent room on the seventh floor were detected as successively positive for the novel coronal nucleic acid. The index cases and infected case at a different layer had no direct contact before and after entering the hotel and were not the close contacts of the same confirmed case of coronavirus disease 2019 (COVID- 19), but the virus gene sequencing results were highly consistent. After investigation, there were no external windows of the rooms they lived in, the air conditioning system of the rooms was a fan coil unit and the central air conditioning air supply system to supply air partly taken from the outdoor and partly from the corridor, the sewage and drainage pipes in bathrooms of the fifth to eighth floor for quarantine did not directly exhaust from the top through the vertical pipes but were gathered to a horizontal pipe at the top of the eighth floor and then exhausted through the roof exhaust fan, which was always closed due to elevator maintenance during the quarantine period.…”