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Al Haddrell Profile picture
@ukhadds
Jun 22, 2023 • 3 tweets • 1 min read • Read on X
I’m proud to have our latest research published on how long #SARSCoV2 remains infectious while airborne! We studied the fundamental processes that drive the loss of viral infectivity in the aerosol phase. #COVIDisAirborne

Here’s a thread going over some of the findings. Image
@ParentMishmash Interesting question btw. Actually, all of your questions have been. Thanks!
@J__Doh Here are the specific values. So, about 10 to 20 times faster decay in sunlight (depending on the season). Image

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More from @ukhadds

Al Haddrell Profile picture
Sep 16
Are respiratory aerosol liquid, solid, neither or both? What about the virus, where does it go? Let's get into this.
We published some work on this previously where we studied how respiratory aerosol changes once it is exhaled.

tandfonline.com/doi/full/10.10…
Once exhaled, the aerosol will begin to lose water. The rate in which the aerosol loses water will depend on the humidity (loses size faster in dry air). The humidity will also determine both the final size and particle structure. Image
Read 6 tweets
Al Haddrell Profile picture
Sep 15
There's been a lot of discussion about the size of exhaled aerosol that contains the most virus. For the most part, it's thought to be in the ~1 to ~5 micron range. There's a little bit of variation between studies, but that's roughly the size of concern (“Viral”).
Image
If you are curious, this is due to a combination of the size distribution of exhaled aerosol and maximum conc that the virus can grow in the respiratory fluid. Here we looked at aerosol size, others have looked into the viral load as a function of size.tandfonline.com/doi/full/10.10…
So, N95 masks work well in filtering out the aerosol size region that is most associated with airborne viral transmission. The key really does come down to fit.

hse.gov.uk/respiratory-pr…
Read 6 tweets
Al Haddrell Profile picture
Aug 14
Huge paper exploring the relationship between exhalation aerosol counts and CO2 has just been published.

Take home message: CO2 and aerosol strongly correlate in silence. Vocalisation causes this relationship to breakdown (way more aerosol than CO2).
pubs.acs.org/doi/10.1021/ac…
This has huge implications on how CO2 can be used to estimate the aerosol counts in a room. Noise matters!!

I've mentioned this work previously, it's great to see it finally published so everyone can have a good look. Image
I mentioned this work in a previous thread where I discussed the many ways in which CO2 is associated with Covid transmission.

Read 8 tweets
Al Haddrell Profile picture
Aug 5
"How does humidity affect SARS-CoV-2 transmission?"

Whenever this question comes up, the answer I give is along the lines of “it’s complicated”.

So, what exactly do I mean (a 🧵)?

Context: When considering airborne transmission of a respiratory virus, numerous factors are involved.

They ALL matter.

Moreover, they are all independent. Meaning, a certain parameter may affect each factor differently. Image
Since the dawn of the field (1950s/60s), the airborne survival of viruses has been measured as a function of relative humidity (RH) and temperature. There are numerous reasons for this, such as to understand viral transmission and to inform about why the virus decays. Image
Read 15 tweets
Al Haddrell Profile picture
Aug 3
Given the unusually high number of swimmers catching Covid in the Olympics, many have hypothesized as to why. I’ve seen a few people point to some work we published on how environmental factors affect SARS-CoV-2’s aerostability.

Some thoughts🧵:

Context:

When respiratory aerosol is exhaled, the dissolved CO2 in the fluid (in the form of HCO3) leaves the aerosol over the course of a couple of minutes. When the CO2 leaves, the pH of the aerosol reaches >10.3.

The high pH drives viral decay. Image
We have reported that anything that can limit this increase in aerosol pH, such as nitric acid or CO2, slows the airborne viral decay rate. This, in turn, will increase the risk of transmission. Image
Read 14 tweets
Al Haddrell Profile picture
Jun 26
Given that the COVID numbers are on the rise, I thought I’d it useful to share some our research team’s work looking at the interplay between CO2, aerosol, SARS-CoV-2, and airborne transmission. 🧵 Image
SARSCoV2 is spread primarily through the air via aerosol. Meaning, the amount of aerosol a person produces will to some degree correlate with the amount of virus exhaled. Our group has done of studies into how different activities affect aerosol production
tandfonline.com/doi/full/10.10…
The amount of aerosol a person exhales is correlated with how loud they are talking/singing. Perhaps a reason why there have been no super spreader events reported in a library (?) Image
Read 13 tweets

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