I've seen a lot of people getting mad at the WHO's use of "puff cloud" for exhaled aerosols. I don't want to jump on anyone's post about it and come off as argumentative about it, but, can someone please explain to me why this is considered an absurd idea?
It's a fairly well established way to discuss aerosols. When you breathe out, it doesn't rocket across whatever space you're in to fill the room. Dispersal takes time, and there's temperature differences that can lead to some cohesion, of sorts, of your exhaled "cloud." I think this has been something aerosol transmission people have been using for years.
Just looking though papers I've bookmarked over the last few years, pretty much everything that models exhaled air uses the term "cloud" including Professor Jimenez's oft cited 2021 paper "How did we get here: what are droplets and aerosols and how far do they go? A historical perspective on the transmission of respiratory infectious diseases"
https://royalsocietypublishing.org/doi/pdf/10.1098/rsfs.2021.0049
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9430019/
Yesterday when I wrote this, I didn't know about this article:
Now I understand why people are upset.
First and foremost, please read the document and not just hot takes about it.
https://iris.who.int/bitstream/handle/10665/376496/9789240089181-eng.pdf
I think the very first paragraph of the article is wrong:
"Airborne viruses will be called "pathogens that transmit through the air” under new terminology the World Health Organization hopes will end a scientific rift that hampered the early response to COVID-19."
The document's not even about "viruses" to begin with. It's about "pathogens" which are defined by The American Heritage Dictionary as:
"An agent that causes disease, especially a virus, bacterium, or fungus."
We're all here discussing the fact that language matters, and right off the bat we have imprecise language, minimizing the science, in this article. It's not JUST about viruses. This is important.
Further, they are not saying that airborne viruses will be called "pathogens that transmit through the air." In fact, they define airborne spread as...."airborne transmission" and you don't even have to go far. It's right there in the Executive Summary. They even put "airborne transmission" in bold.
I think what everyone is arguing about is "descriptor" vs "definition" in the end.
A descriptor is a term that can be used to describe or identify.
"The descriptor ‘through the air’ can be used in a general way to characterize an infectious disease where the main mode of transmission involves the pathogen travelling through or being suspended in the air."
No one has attempted to change the definition of airborne in this document as I've seen at least half a dozen people declare.
"Under the umbrella of the ‘through the air’, two descriptors can be used:
•‘Airborne transmission/inhalation’: Occurs when IRPs expelled into the air as described above and enter, through inhalation, the respiratory tract of another person and may potentially cause infection. This form of transmission can occur
when the IRPs have travelled either short or long distances from the infectious person. The portal of entry of an IRP with respiratory tract tissue during airborne transmission can theoretically occur at any point along the human respiratory tract, but preferred sites of entry may be pathogen specific. It should be noted that the dis-
tance travelled depends on multiple factors including particle size, mode of expul-
sion and environmental conditions (such as airflow, humidity, temperature, setting, ventilation).
•‘Direct deposition’: Occurs when IRPs expelled into the air following a short-range
semi-ballistic trajectory, then directly deposited on the exposed facial mucosal sur-
faces (mouth, nose or eyes) of another person, thus, enter the human respiratory tract
via these portals and potentially cause infection."
Airborne transmission is there. It's described. It's a term that you can use colloquially or technically going forward and say, confidently, that the WHO says so.
To get to the heart of the "puff" matter here, let's go all the way down to the end of the Bloomberg article.
"Still, Greenhalgh, professor of primary care health sciences at the University of Oxford, said Thursday that "airborne” best describes respiratory pathogens that are transmitted through the air.
"WHO wants to introduce terms like ‘puff cloud,’” she said in a post on X. "This is a retrograde step. I for one won’t be playing ball.”"
I fear she has not read the document, nor even the Executive Summary. Airborne DOES best describe it, and that's why they literally described it as airborne. The word "airborne" is used 65 times.
Rather than finding the WHO's declaration as a "retrograde step" you want to know what I found to be a retrograde step? Bloomberg quoting Professor Greenhalgh, who is not an aerosol scientist at all, and whose bio apparently won't use the term "mask" for how we should move forward.
"With colleagues at Oxford, I’ve helped set up a rapid review service for answering questions from the research literature. I’ve been digging out the evidence base on whether or not the public should be wearing face coverings as we move out of lockdown. I think they should."
I've noted before that it seems to depend on your instance as to where it cuts that off. At least here versus my zeroes account often show it differently. The size of the preview it shows for the first link differs across instances, too. I sincerely appreciate the feedback, though. I know I need to work on my scientific communication skills and I never would have even noticed, or thought about that!
@BE
Thank you very much!
For even more clarity, you may want to edit so that the 'click to read more' doesn't show up right after you quote the wrong part, and before you give the correct information 🙂
Or is that just me? I'm using the generic Mastodon web app