The risk of aerosol transmission is not yet fully integrated into institutional COVID safety and prevention policies, which continue to focus on deep-cleaning and two-metre physical distancing, while overlooking ventilation and air filtration.
Current evidence supports the aerosol route as an important mode of transmission of COVID-19. Virus-laden aerosols can infect susceptible contacts through shared room air, but they are also concentrated at close proximity – like smoke.
Control strategies targeting close-proximity transmission, such as physical distancing and mask wearing are well-established and remain critical to reduce aerosol transmission risk. For transmission in shared room air, however, ventilation and air filtration become even more important, as expelled aerosols from breathing, talking or exercising build up in poorly ventilated spaces.
We know that many buildings and residences in our communities have substandard ventilation. To reflect the current scientific evidence, leaders should take the following actions:
- Update COVID-19 guidance to reflect the risk of aerosol transmission of COVID-19
- Engage engineers and other ventilation specialists to develop clear ventilation standards for indoor institutions and integrate these standards into the reopening guidelines for businesses with a higher risk of aerosol transmission (restaurants, bars and gyms)
- Mandate and fund ventilation assessments and upgrades of essential public institutions such as schools and long-term care homes
- Promote strategies to reduce transmission risk in private homes and businesses through clear public health messaging and education (e.g. promoting indoor mask use even when distanced, routinely opening windows to refresh the air, regular HVAC maintenance and filter replacement, turning on available vented range hoods and bathroom exhaust fans)
- Recommend and deploy carbon dioxide (CO2) monitors as a surrogate measure of adequate ventilation (i.e. CO2 concentrations above 1000 PPM significantly increased the risk of becoming infected with TB. Improving the building ventilation to a CO2 concentration of 600 PPM stopped TB outbreak in its tracks.)
- Promote portable air filtration (HEPA) units or low-cost homemade devices using MERV-13 filters and box fans
Example of workplace prevention measure
Since COVID-19 transmits more easily in closed environments with poor ventilation, indoor air quality is a prime concern.
To contain transmission, the following three strategies should be kept in mind:
- Maximize the ventilation of outdoor air
- Maintain between 40% and 60% relative humidity at all times
- Utilize air treatment and optimal air filtration
The issue of poor indoor air quality is not new. “Sick Building Syndrome” demonstrates that poor indoor air quality has health effects. Poor ventilation exacerbates the presence of many sources of air contamination, including VOCs, bacteria, mold, and viruses. Inadequate ventilation stems from long-held energy conservation standards focused on airtight buildings with minimal airflow. New green technologies enable higher airflow from the outside.
Using only one of the above strategies is not a sure-fire way to combat the virus but using a combination of these strategies will minimize the spread.
Specific strategies to reduce indoor aerosol transmission of COVID-19 are adeptly summarized in:
- Canada’s Chief Science Advisor Expert Panel on COVID-19 bioaerosol report
- Occupational Safety and Health Administration (OSHA) Alert
- Harvard TC Chan Risk Reduction Strategies for
Reopening Schools Report.
(adapted from Ventilation not ventilators – an open letter Nov. 24, 2020)
LETTER: “Ventilation not Ventilators”
https://assets.documentcloud.org/documents/20417299/ventilation-not-ventilators-an-open-letter-nov-24-3.pdf November 24, 2020 Hon. Christine Elliott Deputy Premier of Ontario, Ontario Minister of Health and Long-Term Care Dr. David Williams, MD, MHSc, FRCPS Chief Medical Officer of Health, Ministry of Health and Long-Term Care Dr. Brian Schwartz, MD, MScCh Vice-President, Public Health Ontario Dear Hon. Christine Elliott, Dr. David Williams and Dr. Brian Schwartz, […]
Kurnitski, J., A. Boerstra, et al. 2020. REHVA COVID-19 guidance document, “How to operate and use building services in order to prevent the spread of the coronavirus disease (COVID-19) virus (SARS-CoV-2) in workplaces.” March 17 , 2020
In this document REHVA summarizes advice on the operation and use of building services in areas with a coronavirus disease (COVID-19) outbreak, in order to prevent the spread of COVID-19 depending on HVAC or plumbing systems related factors. REHVA published its first COVID-19 guidance mid-March 2020. After two updates (April and August), the fourth version […]
Horve, P.F., Lloyd, S., et al. 2020. “Building upon current knowledge and techniques of indoor microbiology to construct the next era of theory into microorganisms, health, and the built environment.” J Expo Sci Environ Epidemiol. 2020 Mar;30(2):219-235.
In the constructed habitat in which we spend up to 90% of our time, architectural design influences occupants’ behavioral patterns, interactions with objects, surfaces, rituals, the outside environment, and each other. Within this built environment, human behavior and building design contribute to the accrual and dispersal of microorganisms; it is a collection of fomites that […]
Tang, J.W. and Li, Y. 2019. “The airborne microbiome – implications for aerosol transmission and infection control.” BMC Infectious Diseases 2019 19:755
Many infectious diseases, such as tuberculosis, whooping cough, Aspergillus and other fungal infections, human and avian influenza, measles, chickenpox, and some of the emerging viruses, such as Middle East Respiratory Syndrome coronavirus (MERS-CoV) can be potentially spread through aerosol transmission. With the advent of deep-sequencing technologies these can be applied to environmental air samples using metagenomic techniques to characterise the presence and variety of […]
Morawska, L., Ayoko, G.A., et al. 2017. “Airborne particles in indoor environment of homes, schools, offices and aged care facilities: The main routes of exposure.” Environ Int. 2017 Nov; 108:75-83.
It has been shown that the exposure to airborne particulate matter is one of the most significant environmental risks people face. Since indoor environment is where people spend the majority of time, in order to protect against this risk, the origin of the particles needs to be understood: do they come from indoor, outdoor sources […]
Stephens, Brent. 2016. “What Have We Learned about the Microbiomes of Indoor Environments?” mSystems Jul 2016, 1 (4) e00083-16
The advent and application of high-throughput molecular techniques for analyzing microbial communities in the indoor environment have led to illuminating findings and are beginning to change the way we think about human health in relation to the built environment. Here I review recent studies on the microbiology of the built environment, organize their findings into […]