New studies have fuelled speculation about COVID-19 spreading through the air, and emphasised the vital role that HVAC systems will play in controlling the virus.
Since the beginning of the outbreak, the World Health Organization has advised that SARS-CoV-2, the virus that causes COVID-19, is mainly transmitted through contact with respiratory droplets.
When someone with COVID-19 coughs, sneezes, talks or even exhales, these relatively large particles – bigger than 5μm – land on nearby objects and surfaces. Other people can become infected with the virus by touching these objects or surfaces, and then touching their eyes, nose or mouth.
The airborne route
As well as respiratory droplets, people produce much smaller aerosols when they cough, sneeze, talk and exhale. Researchers have been keenly investigating whether these can also spread the virus.
A recent study published in Nature investigated the aerodynamic nature of SARS-CoV-2 by measuring viral RNA (ribonucleic acid) in aerosols in different areas of two Wuhan hospitals during the COVID-19 outbreak in February and March 2020. It found elevated concentrations of viral RNA in patients’ toilet areas, but very low levels in isolation wards and ventilated patient rooms.
The study proposes that “SARS-CoV-2 may have the potential to be transmitted via aerosols”. It also notes that “room ventilation, open space, sanitisation of protective apparel, and proper use and disinfection of toilet areas can effectively limit the concentration of SARS-CoV-2 RNA in aerosols.”
The key outstanding question here is whether viral RNA can actually transmit the virus – the study did not establish the infectivity of the virus detected. It recommends that future work explore this topic.
Restaurant case sparks controversy
Although it concludes that the most likely cause of this outbreak was droplet transmission, it notes that the air conditioning system may have helped the droplets travel beyond what is generally considered a “safe” distance, leading to more infections.
The study has also been picked up by news outlets around the world, which have – perhaps rather simplistically – highlighted a link between air conditioning and COVID-19.
But the rigour of the report has been questioned by many, including Bill Bahnfleth, chair of ASHRAE’s Epidemic Task Force. “The conclusions of the EID article are not well-supported by evidence,” he says. The Cooling Post has also lambasted the study.
The role of HVAC
In terms of HVAC systems and COVID-19, the big unknowns are whether aerosol particles can transmit the virus, and also, whether there is any possibility of a particle moving through an air conditioning system from one part of a building to another.
The Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH) notes that “although there is currently no direct research that supports that SARS-CoV-2 can be transferred through workplace HVAC systems, there is similarly no research to say that it can’t.”
In the meantime, there is general consensus around steps that that should be taken with HVAC systems to help prevent the spread of COVID-19. Chief among these is to increase outdoor air ventilation and to ensure that effective air filters are selected and maintained appropriately.
AIRAH has prepared a list of answers to frequently asked questions and is advising building owners and operators to seek qualified advice on measures such as increasing outdoor air ventilation, humidity control and air filters.