There has been a multi-day debate occurring amongst @AntibioticDoc and many engineers and Aerosol scientists, regarding whether there is sufficient evidence to use HEPA filters to mitigate against Airborne Transmission of SARS2.
.@DavidElfstrom points out, the professional bodies overseeing HVAC, filtering, IAQ (even for hospitals!), are the local engineering regulatory bodies + ASHRAE.
@ashraenews, @APEGA_AB have both been unequivocal re. Airborne Transmission & filtration.
4/20
However, it is evident from the following tweets, that @AntibioticDoc, the Co-Chair of the @AHS_media Scientific Advisory Group, doesn't think there's enough evidence to justify the cost of HEPA filters in schools.
"Just because there's evidence of Airborne Transmission, doesn't mean we should mitigate against it during vaccine rollout"
"Just because there's evidence of Airborne, doesn't mean HEPAs are the answer for schools"
6/20
Ok - "So What? Who cares what an Alberta ID thinks about this? Agree to disagree!"
The reason so many of us care, is because @AntibioticDoc is the Co-Chair of the @AHS_media Scientific Advisory Group for SARS2.
Read this document to understand the influence of this group.
7/20
This group reviews/summarizes the evidence, and then provides policy/guidance documents and recommendations to Alberta Health for "operational decision-making".
They are quite literally the scientific gatekeepers for Alberta re. SARS2 policy.
8/20
So it's quite notable that the Co-Chair of this group is stating their isn't sufficient evidence to justify the purchase of HEPA filters in schools.
The main concern, appears to be regarding introduction of "air currents" caused by the filtered air outflow from the HEPA.
9/20
This is a common fear from ID docs, which is steeped in #DropletDogma, and ignorant of fluid dynamics.
The belief is that SARS2 is spread by droplets, which would naturally stay close to a person, unless a HEPA filter or fan is introduced, then it would blow them around.
10/20
First, Aerosols will naturally and randomly disperse throughout a room, without any external fan.
Without adequate ventilation and filtration, the infectious aerosols will build-up in the room like a cloud of smoke.
11/20
Second, I fail to see how natural ventilation (opening windows and doors) is better for this perceived harm, than a HEPA.
Natural ventilation will also induce air currents - but they will be much more unpredictable. Will depend on window installation, Delta T, and wind.
12/20
By this logic, the safest place, would be a perfectly sealed room, with no mechanical ventilation, fans or open windows. All the droplets would magically drop to the floor.
This is wrong - dangerously so. This would result in a hotbox of COVID aerosols. Think smoke.
13/20
HEPAs have an intake for the infectious air, and an exhaust for the clean air (most exhaust straight up). The flow patterns are predictable, and can be considered when installed by professionals. The same is not true with windows- you don't know which way the air will flow.
14/20
The other concern that's been raised is cost. @CorsIAQ has done the math - they are cheap, and have advantages far beyond mitigation of SARS2 transmission.
They are certainly cheaper than retrofitting entire HVAC systems.
Alberta can afford to install HEPA filters in every classroom. The Federal Government transferred $250 Million to Alberta, for the purposes of supporting a safe return to school. This is what that money was for.
Nobody seems to know. But if the current Alberta School Safety measures are any indication, probably a whole lotta Hygiene Theatre.
17/20
In summary, Alberta has $250M to facilitate a safe return to school in Sept. The chance they will spend any of that on Airborne Mitigations, like HEPA filters, is slim to none, given that the Scientific Advisory Group states there isn’t enough evidence to justify the cost.
18/20
This is a pretty distressing situation for Alberta. The emperor has no clothes.
Talk to your local schools/school boards directly. Point them to mechanical engineering/HVAC experts like @marwa_zaatari.
For those following this HEPA filter thread – this is a really important acknowledgement. It’s clear from the thread, and this particular tweet, that many Infectious Disease experts still doubt that aerosol transmission is an important/mitigable transmission route for SARS2🧵 1/
While they acknowledge aerosol transmission can occur, they believe it is a rare event occurring in special circumstances, and is therefor not worth the $ to mitigate.
Eg. re HEPAs: "We need to resource by best impact", "Changes need rigorous justification and business case".
2/
See my pinned tweet for a thread summarizing the overwhelming evidence that Aerosol Transmission is an important and mitigable route. At the end, I provided a reference list and posed a question to the ID holdouts - no responses yet. 3/
During Friday's debate with @kprather88 and @DFisman, Dr. Conly raised a fairly common counter-point for why he thinks COVID is NOT Airborne: the relatively low Secondary Attack Rate (SAR) and Reproduction Rate (R0).
Let's unpack this flawed argument in a 🧵
1/
Dr. Conly states the SAR is 3 to 10%, with a household mean of 18%.
He then correctly points out that there is significant heterogeneity within the data, which means some people transmit to no contacts, while others transmit to everyone.
2/
After admitting to the heterogeneity, he cautions we "have to be careful not to draw conclusions" from these superspreaders... eg. Chalet (73% SAR), Choir (53%), and Diamond Princess (58.9%). He suggests there were "extenuating circumstances", and seems to dismiss them. 🧐
3/
As Dr. Conly reminded us on Friday, when considering Airborne Transmission, "it's very important to take into consideration the very very complex environment".... "direction of airflow, the number of air changes, temperature, relative humidity... its veeery very complex"
2/
This is actually NOT "complex" for Aerosol scientists, mechanical engineers, building scientists, and other experts in fluid mechanics. Due to the Pandemic, these experts have diverted their brainpower to this problem. See summary of studies below.
Let's unpack Dr. Conly on the Precautionary Principle.
Q: Why weren't HCW provided N95s, given the advanced warning that SARS2 might be Airborne?
Conly: "I need to see a much higher level of evidence..."
(🤔 That's not how the Precautionary Principle works)
🧵 1/
He then makes a pretty bold claim:
"certainly from our experience in Alberta, in Phase 1" the HCWs wore "gowns, gloves, medical masks"... and "not a single HCW transmission"... despite "highly infectious, hot viral patients"
*Phase 1* is defined here: MARCH-APRIL 2020
2/
So why the "Phase 1" qualifier? Why is he using evidence from a 1 to 2 month period that was over a year ago, and extrapolating out to "8 months of continuous contact time", rather than just telling us what happened during the past year?
Re. "Is this really a debate?". Watch this video for yourself...
While this is from July 2020... so far there has been no public movement from Dr. Conly or the WHO IPAC committee on this issue. If anything they have dug-in their heels further.