#17,468
Regardless of what happens with COVID-19 going forward, we can be pretty confident that it won't be our last severe pandemic. Fortunately, buried within the thousands of studies published on the pandemic over the past 3 years we have an immense amount of data on how novel viruses spread, and ways to reduce their impact.
Of course, having the information - and learning from it - are two different things. But I digress.
Twenty years ago, during our first brush with a coronavirus epidemic (see SARS and Remembrance), one of the most memorable events was the massive outbreak at the Amoy Gardens Apartment in Hong Kong where 330+ residents were infected.
A 2006 review found:
Environmental transmission of SARS at Amoy Gardens.
McKinney KR1, Gong YY, Lewis TG.
Abstract
Recent investigations into the March 2003 outbreak of SARS in Hong Kong have concluded that environmental factors played an important role in the transmission of the disease. These studies have focused on a particular outbreak event, the rapid spread of SARS throughout Amoy Gardens, a large, private apartment complex. They have demonstrated that, unlike a typical viral outbreak that is spread through person-to-person contact, the SARS virus in this case was spread primarily through the air.
High concentrations of viral aerosols in building plumbing were drawn into apartment bathrooms through floor drains. The initial exposures occurred in these bathrooms. The virus-laden air was then transported by prevailing winds to adjacent buildings at Amoy Gardens, where additional exposures occurred. This article reviews the results of the investigations and provides recommendations for maintenance and other measures that building owners can take to help prevent environmental transmission of SARS and other flulike viruses in their buildings.
Despite the experience at Amoy Gardens, the spread of COVID aerosols via ventilation and air conditioning systems was initially downplayed (see June 2020's ECDC Technical Report: Heating, ventilation and air-conditioning systems in the context of COVID-19), which reassured.
In conclusion, the available evidence indicates that:
- Transmission of COVID-19 commonly occurs in closed indoor spaces.
- There is currently no evidence of human infection with SARS-CoV-2 caused by infectious aerosols distributed through the ventilation system ducts of HVACs. The risk is rated as very low.
That view would eventually change as we began to see more and more reports of unexpectedly efficient COVID spread through large residential and/or commercial buildings, including:
EID Journal: Probable Aerosol Transmission of SARS-CoV-2 through Floors and Walls of Quarantine Hotel, Taiwan, 2021
EID Journal: Detection of SARS-CoV-2 on Surfaces in Quarantine Rooms
EID Journal: Aerosol and Surface Distribution of SARS-CoV-2 in Hospital Wards, Wuhan, China
CCDC Weekly: Field Simulation of Aerosol Transmission of SARS-CoV-2 in a Special Building Layout
To this list we can add the following report in the journal Public Health in Practice on an outbreak at a high-rise residential building in Shenzhen, China which found evidence that (like Amoy Gardens) faulty plumbing venting was probably behind the rapid spread of the virus.
I've only reproduced the abstract below, so you'll want to follow the link to read the full study. I'll have a postscript when you return.
High-rise buildings: A risk factor in the COVID-19 Omicron epidemic period
Author links open overlay panelHongxin Lyu a, Xianwu Zhong b, Qiaojie Huang c, Linkai Zheng d, Hongbiao Chen a, Song Cai cShow more
https://doi.org/10.1016/j.puhip.2023.100389Get rights and content
Under a Creative Commons license
Abstract
Objectives
This study aimed to investigate possible viral transmission scenarios inside a high-rise building during the Omicron phase of the COVID-19 pandemic.
Study design
Cross-sectional study design.
Methods
In order to determine the pathogenicity of the Omicron variant of SARS-CoV-2, demographic, vaccination and clinical data were collected from COVID-19 positive cases during an outbreak in a high-rise residential building in Shenzhen, China, in early 2022. The pattern of viral transmission inside the building was determined through field investigation and engineering analysis. The results highlight the risk of Omicron infection in high-rise residential buildings.
Results
Symptoms of infection with the Omicron variant are predominantly mild. Younger age has a greater impact on the severity of disease than vaccination status. Each floor of the high-rise building investigated contained 7 apartments, numbered 01 to 07, positioned in the same layout on each floor. The drainage system included vertical pipes from the ground to the roof of the building. There were statistically significant differences in infection rates at different time points and incidence ratios between apartment numbers ending in 07 (type 07) and other apartments (P < 0.001).
Households with early disease onset were concentrated in apartment type 07 and the severity of their disease was more severe. The incubation period of the outbreak was 5.21–5.31 days and the time-dependent reproduction number (Rt) was 12.08 (95% confidence interval [CI] 7.66, 18.29). Results suggest both non-contact and contact viral transmission may have contributed to the outbreak. The drainage system in the building allows aerosol regurgitation, thus indicating that the structure of the building may have led to spread of the virus from the sewage pipes. Infections in other apartments may have been as result of viral transmission in the elevators and intimate family contact.(Continue . . . )
Conclusions
Results from this study suggest that Omicron transmission was likely to be via the sewage system, supplemented by contact transmission in the stairs and elevators. The environmental spread of Omicron needs to be highlighted and prevented.
Until relatively recently the importance of aerosol transmission of viruses and bacteria has been downplayed, with many citing an `effective range' of less than two meters, a very brief `suspension time', and short-term viability in the environment as limiting factors.
But studies, like the one above, suggest that we underestimate the durability and tenacity of these viruses.
In 2014's ICAAC Video: How Quickly A Virus Can Spread In A Building, we looked at an experiment on fomite transmission, which they described as:
Using tracer viruses, researchers found that contamination of just a single doorknob or table top results in the spread of viruses throughout office buildings, hotels, and health care facilities. Within 2 to 4 hours, the virus could be detected on 40 to 60 percent of workers and visitors in the facilities and commonly touched objects. Simple use of common disinfectant wipes reduced virus spread by 80 to 99 percent.We've even seen evidence that viruses may be aerosolized via a more circuitous route (see Nature: Another Toilet Plume Study To Consider), and even some evidence of long-distance spread of avian flu via dust particles (see Nature: Airborne Transmission May Have Played A Role In Spread Of U.S. 2015 HPAI Epizootic).
While vaccines, antivirals, and NPIs will be our main defense against the next pandemic, there are roles for better building design, improved ventilation and filtration systems, and better cleaning and disinfecting procedures.