Not enough data to know whether the virus that causes COVID-19 can spread through a building’s ventilation system
The coronavirus can be spread through buildings’ heating, ventilation and air conditioning system (HVAC)
Unsubstantiated (insufficient data)
A team of researchers based out of the University of Alberta claims the virus that causes COVID-19 can spread through building ventilation systems. Our verdict is that this claim is unsubstantiated: there is still not enough data to clearly demonstrate this.
In April 2020, a Canadian federal grant was awarded to the University of Alberta, to study mitigation strategies against COVID-19 transmission through heating, ventilation and air conditioning (HVAC) systems. This is a preliminary study with no conclusions yet. While there are some studies suggesting the possibility of airborne transmission and a group of scientists have asked the World Health Organization to reconsider its position, there is still no scientific consensus and WHO and the US Centers for Disease Control and Prevention maintain that more research needs to be urgently conducted to conclude that the COVID-19 virus is airborne. Until then, it is likely that airborne transmission is possible, but researchers are still not sure how frequently. If and when this mode of transmission is confirmed, further studies would have to be conducted to determine if HVAC systems can spread the virus.
Droplets are not defined as airborne transmission
The US Centers for Disease Control and Prevention (CDC) explains that the coronavirus spreads through respiratory droplets, produced through exhalation, coughing or sneezing. These can only travel a short distance, before falling, which is why we have physical distancing rules of 2 meters. People can become infected by touching an infected surface and then touching their mouth, nose or eyes before washing their hands.
Even if these droplets technically travel through the air, they are not considered, in technical terms, as airborne transmission. The World Health Organization (WHO) explains that airborne transmission is defined as the transmission of particles that are smaller than the heavy droplets that the coronavirus spreads through and can travel farther and stay in the air longer. The WHO maintains that this is not the case for the new coronavirus.
Previously, Australian scientists have argued that it is likely that COVID-19 can be spread through the air. They make this argument because this strand of the virus, also known as SARS-CoV-2, has a predecessor, SARS-CoV-1, which was airborne. This is still a theory and not yet corroborated by actual studies.
In an open letter dated July 6, 2020, 239 scientists in 32 countries urged the medical community to recognize the potential for airborne spread of COVID-19. They cite multiple studies and acknowledge that while there is not yet universal acceptance of airborne transmission of SARS-CoV2 in the medical community, there is enough preliminary evidence to encourage precautions to be taken. According to this letter, there is “significant potential” for spread through inhalation at short to medium distances, which they define as up to several meters, or room scale.
In response, WHO updated its brief on modes of transmission for the first time since March 29 2020. They are aware of studies which have evaluated the presence of COVID-19 RNA in air samples but is not indicative of viable virus that could be transmissible. WHO acknowledged that research is “urgently needed to investigate such instances and assess their significance for transmission of COVID-19.” It is important to know whether viable virus is found and what role it may play in transmission.
Can HVAC systems still propel heavy droplets?
The University of Alberta’s study was in part inspired by an outbreak at a restaurant in a southern Chinese city, linked to its air conditioning unit. According to a paper published by the Guangzhou Yuexiu District Center for Disease Control and Prevention, scientists studying a cluster of COVID-19 people who had eaten at that restaurant found that the strong airflow from the AC “could have propagated droplets” and that in this case, the air-conditioned ventilation prompted the droplet transmission. They did not find that the coronavirus was airborne.
However, this is only one reported incident with an exceedingly small sample size in a restaurant where the overall ventilation was poor. There have not been other reported cases of HVAC systems carrying droplets. In addition, the authors of the study share limitations that are important to consider. They did not conduct an experimental study, which would have mimicked an airborne transmission route within that restaurant, nor did they estimate the risk of infection through other routes by testing asymptomatic family members and other diners. No other guests and staff members of the restaurant tested positive for COVID-19.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), a professional association, insists that HVAC systems play only a small role in disease transmission generally and COVID-19 is not an exception. Other routes of transmissions, like person-to-person contact, are much more likely.
Is there enough data to make a case?
In this case there is insufficient data to be conclusive about the role of HVAC systems in the transmission of COVID-19. Our verdict is that the claim published in the Canadian newspaper The National Post is unsubstantiated.
Preliminary research does not mean scientific consensus, which will take much longer, and consensus can evolve and change as new research is conducted. The virus that causes COVID-19 is a novel virus, meaning it was previously unrecorded until this pandemic. Usually when academic research studies are released, they are peer reviewed, which means they are reviewed by outside experts to judge their quality, credibility and reliability. As Stanford University news explains, because this is a crisis situation, there has been a serious need for information and solutions as soon as possible and a lot of information is being released as “pre-prints”, without the usual high standards of this peer-reviewed process. It is done to encourage collaboration and increase the speed of results, but it does create a risk that studies are partially or incorrectly completed.
How to protect yourself in the meantime?
In addition to WHO’s recommendations for physical distancing and routine cleaning, there are a number of precautions you can take regarding HVAC systems. For inside your home, the US CDC recommends washing your hands regularly for 20 seconds, avoid contact with people who are sick, even inside your home, and clean and disinfect used surfaces daily. If possible, the sick person should stay in a separate room. If there is a sick person, WHO recommends ensuring that plumbing is well-maintained to avoid contaminating the plumbing or ventilation system through aerosolized faecal matter in the bathroom. Alternately, if possible, the sick person should use a separate bathroom.
For public buildings, to further reduce risk, ASHRAE recommends increasing outdoor air ventilation, disabling on-demand ventilation, opening minimum outdoor air dampers as high as 100%, eliminating recirculation, and increasing central air filtration. According to ASHRAE, HVAC systems provide ventilation and filtration that can keep the air clean and reduce the concentration of possible pathogens. They also recommend running HVAC systems on minimum outside air when buildings are unoccupied.
The open letter from scientists recommends minimizing air recirculation and supplementing general ventilation with other airborne infection controls, like local exhaust, high efficiency air filtration, and germicidal ultraviolet lights. The letter also recommends not overcrowding public buildings and public transport. WHO recommends checking that building ventilation, air exchange, and dehumidification equipment of covered pools are in good working order.
The collision repair news site, Repairer Driven News, asked the CDC for recommendations about cars and HVAC systems. According to the CDC spokesperson, the CDC has not issued recommendations for decontamination of building HVAC systems that have potentially been exposed to the coronavirus and that, as of yet, there is no evidence that the virus can remain viable in these systems. This is because, so far, experts have found that the virus loses its ability to infect people naturally within a matter of hours or days.
In the case of cars, the CDC recommended that rideshare, taxi, and limo drivers not use the recirculated air option for the car’s ventilation during passenger transport. They suggested using the car’s vents to bring in fresh outside air and/or lower the vehicle windows instead.
If you think your car may have been contaminated with the COVID-19 virus, the CDC spokesperson recommends a wait period of 24 hours with maximum sun exposure to deactivate any traces of the virus that may be present. When the vehicle is outside, vacant with its doors open and windows down, ensure that the system is not set to recirculation mode, set the heater to maximum temperature, and turn on the blower motor at maximum setting for 5 minutes. Finally, after completing one or both of these steps, disinfect the car’s surfaces.
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July 30, 2020
We updated this text on July 2020, to reflect the continuing conversation between the scientific community and the World Health Organization on whether the SARS-CoV-2 virus which causes COVID-19 is airborne. Our verdict, which reflects our fact-checking about the potential transmission of SARS-CoV-2 through heat, ventilation and air conditioning (HVAC) systems has not changed; more studies are needed to arrive at a firm conclusion on this particular topic. A group of scientists have encouraged precautions be taken in light of the potential for spread of SARS-CoV-2 through airborne transmission.
Here is the substantive content that we added:
In an open letter dated July 7, 2020, 239 scientists in 32 countries urged the medical community to recognize the potential for airborne spread of COVID-19. They cite multiple studies and acknowledge that while there is not yet universal acceptance of airborne transmission of SARS-CoV-2 in the medical community, there is enough preliminary evidence to encourage precautions to be taken. According to this letter, there is “significant potential” for spread through inhalation at short to medium distances, which they define as up to several meters, or room scale.
In response, WHO updated its brief on modes of transmission for the first time since March 29 2020. They confirmed reports of airborne transmission but did not acknowledge that COVID-19 could be spread through airborne transmission. The WHO acknowledged that research is “urgently needed to investigate such instances and assess their significance for transmission of COVID-19.”
Earlier in the text, we also added the caveat to distinguish between airborne transmission of the virus and transmission through HVAC systems: “Until then, it is likely that airborne transmission is possible, but researchers are still not sure how frequently. If and when this mode of transmission is confirmed, further studies would have to be conducted to determine if HVAC systems can spread the virus.”
American Society of Heating, Refrigerating and Air-Conditioning Engineers https://www.ashrae.org/file%20library/technical%20resources/ashrae%20journal/2020journaldocuments/72-74_ieq_schoen.pdf
Environment International https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7151430/
Stanford University News https://news.stanford.edu/2020/04/06/open-science-era-covid-19/
US Centers for Disease Control and Prevention https://www.cdc.gov/coronavirus/2019-ncov/faq.html https://www.cdc.gov/coronavirus/2019-ncov/community/organizations/rideshare-drivers-for-hire.html
World Health Organization https://www.who.int/news-room/commentaries/detail/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations#:~:text=According%20to%20current%20evidence%2C,transmission%20was%20not%20reported. https://www.who.int/westernpacific/emergencies/covid-19/information/physical-distancing https://apps.who.int/iris/bitstream/handle/10665/331937/WHO-2019-nCoV-Hotels-2020.2-eng.pdf
Journal of Clinical Infectious Diseases
The coronavirus can be spread through buildings’ heating, ventilation and air conditioning system (HVAC)
June 16, 2020
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