The risk of the airborne transmission of disease correlates with the amount of infectious exhaled aerosol. Since people exhale CO2 with aerosol, its conc has been used as proxy for exhaled aerosol In this article, researchers propose a new way to estimate risk of transmission
Here’s a link to the article (the first author is Henry Oswin, a former PhD student from our group who is currently working with Lidia Morawska): sciencedirect.com
sciencedirect.com
For a variety of reasons, CO2 may not be a good proxy for exhaled aerosol. eg, it will underestimate the risk when people are talking, or overestimate when filtration is used. I walked through some of this in my explainer video (excerpt shown below): youtu.be
So, rather than using CO2 to estimate risk, the authors propose developing a technique to measure the amount of just the exhaled aerosol in a room. The challenge then becomes, how do you determine an aerosol is an exhaled aerosol? Infectious microbes are transmitted on exhaled aerosol. The initial composition of exhaled aerosol is essentially saliva or lung fluid. Meaning it’s a complex mixture of salts, sugars, surfactants, mucins and proteins…. And microbes (the flora). en.wikipedia.org
en.wikipedia.org
Bodily fluids will contain many microbes that are nonharmful or even beneficial. In this study, they collected exhaled aerosol and measured something they call the airborne respiratory microflora (ARM). This is essentially the mixture of non-pathogenic microbes in exhaled aerosol.
They use PCR to identify the DNA of the various microbes in exhaled aerosol. To do this, they had volunteers sing “Happy Birthday” and collected the exhaled aerosol with a bioaerosol sampler. They then tested for the specific microbes DNA and found many copies.
They tested their technique in a hospital and found that it worked in a complex environment. Shown here the relative amount of respiratory aerosol detected in different places in a hospital.
They also looked for SARS-CoV-2 in their air samples and found them as well. They were then able to normalize the viral load to the amount of exhaled aerosol. This tells you where there are more infectious exhaled aerosol in given space.
PCR takes a while to report a signal, so these measurements aren’t in real-time. That said, it’s an interesting approach and step in a new and exciting direction. Anyway, those are my thoughts on this cool new study. A good proof of concept. Check it out.