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New research raises more concerns about airborne transmission of COVID-19

One scientist says, “The world should face the reality.”

As an architect teaching sustainable design at Ryerson School of Interior Design in Toronto, I have been preoccupied for some years with healthy buildings and the intersection of disease and design, and more recently, how COVID-19 will affect the design of our homes, our workplaces, and our cities.

We recently looked at the question of air conditioning, mechanical ventilation and the spread of the coronavirus, quoting chapter and verse from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the organization that recommends standards for the industry. That information was a month old, but engineer Shelly Miller points us to a new paper that was just released:

Miller points to an additional paper “authored by Dr. Morawska, who also led our fearless group of scientists in the writing of this current paper.” It has quite the title: Airborne transmission of SARS-CoV-2: The world should face the reality. Dr. Moraska notes that handwashing and social distancing are not enough; they do not prevent infection by inhalation of the virus.

Science explains the mechanisms of such transport and there is evidence that this is a significant route of infection in indoor environments. Despite this, no countries or authorities consider airborne spread of COVID-19 in their regulations to prevent infections transmission indoors. It is therefore extremely important that the national authorities acknowledge the reality that the virus spreads through air, and recommend that adequate control measures be implemented to prevent further spread of the SARS-CoV-2 virus, in particular removal of the virus-laden droplets from indoor air by ventilation.

Dr. Moraska looks at past events, including SARS-CoV-1, which hit Hong Kong and Toronto hard, and which spread in the air, as well as a number of other virus outbreaks, and sees no reason why this one should be different.

“Therefore, all possible precautions against airborne transmission in indoor scenarios should be taken. Precautions include increased ventilation rate, using natural ventilation, avoiding air recirculation, avoiding staying in another person’s direct air flow, and minimizing the number of people sharing the same environment.”

So why isn't this being done? Why is it not raised as an issue of significant importance? It's complicated. Dr. Moraska suspects that it might be due to the fact that it is hard to figure out accurately. But the fact that there are no simple methods for detecting the virus in the air does not mean that the viruses do not travel in the air. She concludes:

To summarize, based on the trend in the increase of infections, and understanding the basic science of viral infection spread, we strongly believe that the virus is likely to be spreading through the air…Therefore, we plead that the international and national authorities acknowledge the reality that the virus spreads through air, and recommend that adequate control measures, as discussed above be implemented to prevent further spread of the SARS-CoV-2 virus.

How can airborne transmission of COVID-19 indoors be minimized?

Lidia Morawska was the lead author (along with Shelly Miller and 33 others from around the world) of the recent study which looked at this question, noting that “inhaling small airborne droplets is probable as a third route of infection, in addition to more widely recognized transmission via larger respiratory droplets and direct contact with infected people or contaminated surfaces.”

Their first and probably most important point is that ventilation should be recognized as an important consideration in dealing with the virus. This isn't just in hospital buildings, which have been designed to have good ventilation, but also:

…in public buildings and other shared spaces, such as shops, offices, schools, kindergartens, libraries, restaurants, cruise ships, elevators, conference rooms or public transport, where ventilation systems can range from purpose-designed mechanical systems to simply relying on open doors and windows. In most of these environments, ventilation rates are significantly lower than in hospitals for various reasons, including limiting airflows for energy and cost savings.

It is important to deal with this now, as “stay-at-home lockdown measures are gradually relaxed, much of the population may return to spending increasing amounts of time in inadequately ventilated workplaces, offices, schools and other public buildings, where they may be exposed to a risk of acquiring viral infections by inhalation.”

Measures that should be taken immediately:

  • Ventilation rates should be increased by system modifications. However, they acknowledge that “this is not via a simple ‘flick of a switch'” as these systems are designed for each building and are complex systems.
  • Avoid air recirculation. This was recommended also by the European and American engineering associations. As I noted earlier, this is not going to be easy in really hot climates. As for split systems (like the one in that restaurant in China) and like the ones found all over North America, which have no fresh air intakes at all, these should just be turned off or supplemented by lots of fresh air through opening windows. Again, this will be very hard in summer in the hotter parts of the country.
  • Air cleaning and disinfection devices may be beneficial. This includes Ultraviolet Light (UVC) systems as discussed earlier. Also, portable air filters and cleaners could help.
  • Minimize the number of people within the same indoor environment in an epidemic. This is a tough one; nobody really knows what the number of people in a given space is safe and what isn't. But their empirical guideline makes sense: “In a school or a supermarket, for example, if the number of infected students or shoppers is low, and the ventilation rate is high, the risk of airborne transmission can be low.” Crowding a bunch of people into a subway or bus is another story.

If implemented correctly, these recommended building-related measures will lower the overall environmental concentrations of airborne pathogens and thus will reduce the spread of infection by the airborne route. Together with other guidance on minimising the risk of contact and droplet transmission (through hand-washing, cleaning of hand-touch sites, and the appropriate use of PPE), these ventilation-related interventions will reduce the airborne infection rates not just for SARS-CoV-2 in the current COVID-19 pandemic, but also for other airborne infectious agents.

There are lots of lessons for architects and engineers here; perhaps it is time to look again at traditional ways of keeping cool again, shading buildings with vegetation and having lots of cross-ventilation, increasing insulation to minimize the need for recirculated air.

But perhaps the most important lesson from all of this is that we have to change the design process; architects can't just design a building and then toss the plans over to an engineer. The mechanical systems and the building design are inseparable – how the air moves, how much is needed. Instead of designing for aesthetics or value or comfort, we have to design for health.

Blood BrothersTaken before we had to social distance/ Lloyd Alter/CC BY 2.0

But there are lessons for everyone else as well: avoid crowds, dine al fresco, wear a mask, support your smaller neighborhood store where you are more likely to be one of a few people in it, or those nice little restaurants with the big garage doors.