Doctors and Engineers Speak the Same Language on COVID-19 Transmission

It's as much about engineering as it is about epidemiology.

Children in an open classroom
Elizabeth McCormick Open Air School, Chicago, USA, 1911.

Library of Congress

Back in March, the World Health Organization (WHO) took a strong position that COVID-19 was not airborne, that it was transmitted through droplets that "are too heavy to hang in the air. They quickly fall on floors and surfaces." This has been the foundation of their advice ever since, and the logic behind the 6-foot social distancing.

But also since March, the building scientists and engineers who deal with air movement have been saying that this is not correct, that there is a long history of studying how viruses move, and they are carried in the air a lot further than 6 feet. Treehugger has been following this closely, as indoor air quality has long been a topic of discussion here.

WHO is still distributing information that many consider to be outdated and ineffective; a one-meter separation is not really relevant, and all that disinfection is not that useful.

The schism got so bad that the engineers (and many doctors) recently started a petition demanding that WHO "recognize the compelling scientific evidence that SARS-CoV-2 spreads by aerosol transmission ('airborne') and urge the WHO to immediately develop and initiate clear recommendations to enable people to protect themselves."

Engineer and building science expert Robert Bean has been on this case for a while, warning that social distancing is totally circumstantial and that as winter comes we face additional challenges with ventilation and humidity control. He explained to Treehugger that "there is definitely a disconnect between professionals that should be collaborating." But this may finally be changing, or at least evolving. A document, "COVID-19 – Lessons Learned and Questions Remaining," summarizes the state of research as of the end of October 2020. There is not a building science engineer among the long list of doctors who contributed to this, but they start off with a quote from William Osler about learning from your mistakes: “You will draw from your errors the very lessons which may enable you to avoid their repetition.” In the section on epidemiology, they address the airborne vs droplet spread controversy by saying there shouldn't be a controversy at all.

"Perhaps the biggest surprise about the issue of airborne spread of SARS CoV-2 is that it has been surprising to so many people. From the beginning of the epidemic, the ability of the virus to spread from person to person has been regularly downplayed by public health officials despite clear evidence of exceptional transmissibility, from the initial explosive spread in Wuhan to its rapid dissemination across China and to the rest of the world. A key lesson learned from this pandemic is that the distinction between 'droplet' and 'aerosol' spread is a false dichotomy that is inconsistent with contemporary knowledge about respiratory aerosols. Aerobiologists have demonstrated that particles produced in the human respiratory tract represent a continuum of sizes."

They explain how the virus can be in large particles or small or anything in between, how it is carried, and these doctors sound a lot like the engineers:

"The likelihood of infection becomes a function of the quantity of virus being produced by the source patient, distance from the source, ambient air flow and whether the producer and potential recipients of the virus are wearing face masks. Smaller particles are much more likely to accumulate in enclosed places with poor air flow and to be transmitted where people are not wearing masks – hence providing a simple explanation for the clear epidemiological evidence that crowded bars, restaurants and gyms favor viral outbreaks and suggesting engineering interventions to reduce the risk of spread."

Carbon Dioxide Monitoring Can Reduce The Risk

How the virus moves
Peng Z, Jiminez JL CC4.0

If one accepts that this is an engineering issue, then one can think of other engineering tools that might help solve the problem. Engineer Shelly Miller wrote in The Conversation that it is difficult to measure the amount of virus that is in the air, or if there is enough fresh air, but measuring CO2 levels is a good proxy.

"Since the coronavirus is most often spread by breathing, coughing or talking, you can use CO2 levels to see if the room is filling up with potentially infectious exhalations. The CO2 level lets you estimate if enough fresh outside air is getting in."

CO2 meters are cheap, and they are being used as the "canary in the coal mine" to determine if there is enough fresh air to dilute the virus. Zhe Peng and Jose Jimenez came to the same conclusion in a study, "Exhaled CO2 as COVID-19 Infection Risk Proxy for Different Indoor Environments and Activities," noting that infected people exhale both CO2 and the virus, so if CO2 levels can be reduced by increased ventilation, the virus levels should be as well.

"CO2 is co-exhaled with aerosols containing SARS-CoV-2 by COVID-19 infected people and can be used as a proxy of SARS-CoV-2 concentrations indoors. Indoor CO2 measurements by low-cost sensors hold promise for mass monitoring of indoor aerosol transmission risk for COVID-19 and other respiratory diseases."

This is now being done in schools, using the CO2 monitor as a way of determining if there is enough ventilation for the number of people in a room of a given size, using a handy Excel spreadsheet calculator from Harvard Healthy Buildings Program.

Joseph Allen of Harvard also tweets some precautions that everyone should consider for Thanksgiving, based on the understanding that this virus is in the air. They used to say this about treating water, but the same applies to air: "The solution to pollution is dilution." Open those windows and if you can, eat outside. Even if WHO is not yet admitting they were wrong, everyone else is getting the message.

View Article Sources
  1. "Coronavirus Disease 2019 (COVID-19)". Centers For Disease Control And Prevention, 2020.

  2. Fang, Ferric C et al. "COVID-19—Lessons Learned And Questions Remaining". Clinical Infectious Diseases, 2020. Oxford University Press (OUP), doi:10.1093/cid/ciaa1654.