Catherine Clase
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catherineclase.bsky.social
Catherine Clase
@catherineclase.bsky.social
4.6K followers 1.5K following 520 posts
Professor of medicine, kidney doc, epidemiologist, editor, mask researcher and advocate (airborne)

@docshumanity.bsky.social

Opinions my own

https://www.doctorshumanity.org/petition
https://maskevidence.org
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catherineclase.bsky.social
Catherine Clase @catherineclase.bsky.social · Jan 21
The idea that 'cloth masks are good only for droplets' still circulates. Many have said this, but it is wrong.

Recommendations about cloth masks, from spring 2020, were based on aerosol evidence

www.acpjournals.org/doi/10.7326/...

#WearTheBestMaskAvailable
1/14
Cloth can block droplets and aerosols, and layers add efficiency. Filtration efficiency for single layers of different types of cotton cloth in a bioaerosol (0.2 µm) experiment was between 43% and 94%, compared with 98% to 99% for fabric from disposable medical masks (2). In a summary of similar observations, single layers of scarfs, sweatshirts, T-shirts, and towels were associated with filtration efficiency of 10% to 40% in experiments using NaCl aerosol (0.075 µm) (3). For tea towel fabric, studied with aerosol-sized particles, filtration efficiency in experiments using a bacterial marker was 83% with 1 layer and 97% with 2 layers, compared with 96% for a medical mask (4). In experiments using virus, 1 layer of tea towel had 72% efficiency and 1 layer of T-shirt fabric 51%, compared with 90% for a medical mask (4). A 2020 study confirms that some fabrics block clinically useful percentages of transmission, even for aerosols and even in single layers; multiple layers improve efficiency (5).
catherineclase.bsky.social
I just signed: please sign and share here and in your networks.

International

secure.avaaz.org/campaign/en/...
Don’t bulldoze our pitch
URGENT: Children in Bethlehem are about to lose the only place where they can play and feel safe. Help them reach FIFA before Israel destroys their pitch. Sign and share.
secure.avaaz.org
January 7, 2026 at 2:16 PM
catherineclase.bsky.social
Between flu and back-to-school, here's a refresher on masks.

All masks work

N95s work best

In health care, N95s work best when you wear them continuously. Targetting risk is less effective. Anecdotally, the number of times I've learned something in an encounter & been grateful for my N95...
catherineclase.bsky.social Catherine Clase @catherineclase.bsky.social · Jan 21
The idea that 'cloth masks are good only for droplets' still circulates. Many have said this, but it is wrong.

Recommendations about cloth masks, from spring 2020, were based on aerosol evidence

www.acpjournals.org/doi/10.7326/...

#WearTheBestMaskAvailable
1/14
Cloth can block droplets and aerosols, and layers add efficiency. Filtration efficiency for single layers of different types of cotton cloth in a bioaerosol (0.2 µm) experiment was between 43% and 94%, compared with 98% to 99% for fabric from disposable medical masks (2). In a summary of similar observations, single layers of scarfs, sweatshirts, T-shirts, and towels were associated with filtration efficiency of 10% to 40% in experiments using NaCl aerosol (0.075 µm) (3). For tea towel fabric, studied with aerosol-sized particles, filtration efficiency in experiments using a bacterial marker was 83% with 1 layer and 97% with 2 layers, compared with 96% for a medical mask (4). In experiments using virus, 1 layer of tea towel had 72% efficiency and 1 layer of T-shirt fabric 51%, compared with 90% for a medical mask (4). A 2020 study confirms that some fabrics block clinically useful percentages of transmission, even for aerosols and even in single layers; multiple layers improve efficiency (5).
January 5, 2026 at 11:08 PM
catherineclase.bsky.social
open.substack.com/pub/charliea...
Venezuela - The Lesson for Canada
Make no mistake, the attack on Venezuela by the Trump regime is not about removing a rogue leader; it is a deliberate attack on international law.
open.substack.com
January 5, 2026 at 1:51 PM
catherineclase.bsky.social
In response to U.S. bombing of Venezuela, and kidnapping the President and First Lady, we are assembling at the Federal Building [55 Bay St. North] at noon to protest actions by the Carney government that have been complicit with these illegal actions.

#HamOnt Hope to see you there!
Monday at noon. 55 Bay Street N. Demonstrate against U.S. Aggression against Venezuela and the Carney government's complicity. We encourage people in the Hamilton area to join us on Monday, the 5th, for an emergency protest about Venezuela. In response to U.S. bombing of Venezuela, and kidnapping the President and First Lady, we are assembling at the Federal Building [55 Bay St. North] at noon to protest actions by the Carney government that have been complicit with these illegal actions. Hope to see you there! [Thanks to Hamilton artist Sonali Menezes for this awesome poster!]
January 5, 2026 at 12:13 AM
catherineclase.bsky.social
Article 2.4 of the UN charter:

All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations
www.un.org/en/about-us/...
United Nations Charter (full text) | United Nations
www.un.org
January 4, 2026 at 7:22 PM
catherineclase.bsky.social
secure.avaaz.org/campaign/en/...
Don’t bulldoze our pitch
URGENT: Children in Bethlehem are about to lose the only place where they can play and feel safe. Help them reach FIFA before Israel destroys their pitch. Sign and share.
secure.avaaz.org
January 3, 2026 at 10:54 PM
catherineclase.bsky.social
www.ctvnews.ca/canada/artic...
Here’s how long it took Canada’s top CEOs to earn what the average Canadian worker makes all year
By 9:23 a.m. on Jan. 2, 2025, Canada’s 100 highest-paid CEOs had already earned what the average Canadian worker made in an entire year, according to a new report.
www.ctvnews.ca
January 3, 2026 at 6:18 PM
catherineclase.bsky.social
“And if you cut [laws] down… do you really think you could stand upright in the winds that would blow then?”
cristianfarias.com Cristian Farias @cristianfarias.com · 4d
Best thing I’ve read this morning, from a human rights lawyer in Mexico. Translation is in the ALT-text.
Twitter thread in Spanish by José Mario de la Garza, a human rights lawyer in Mexico, translated using Google Translate: 1. Overthrowing a dictator sounds morally right. No one mourns a tyrant. But international law wasn't built to protect the good, but to restrain the powerful. That's why it prohibits force almost without exception: not because it ignores injustice, but because it knows that if each country decides whom to "liberate" by force, the world reverts to the law of the strongest. 2. The problem is not Maduro. The problem is the precedent. When military force is used to change governments without clear rules, sovereignty ceases to be a limit and becomes an obstacle. Today it is “overthrowing a dictator”; tomorrow it will be “correcting an election,” “protecting interests,” “restoring order.” The law does not absolve dictatorships, but neither does it legitimize unilateral crusades. Cont’d: 3. The uncomfortable question is not whether a tyrant deserves to fall, but who decides when and how. Because history teaches something brutal: removing a dictator is easy; building justice afterward is not. And when legality is broken in the name of good, what almost always follows is not freedom, but chaos, violence, and new victims. The law exists to remind us of this, even when it makes us uncomfortable. Maduro isn't the problem: he's the face of the problem. Removing him from power would be merely opening the door. Behind him is the machine: Rodríguez, Cabello, the military command, the operators of repression and plunder. If you only change the person at the top and leave the system intact, what follows isn't democracy: it's a reshuffling. And there's something even more difficult: Chavismo didn't just capture institutions, it captured daily life. Economy, media, bureaucracy, employment, fear, favors, blackmail. A country can't be "de-Chavistaized" by decree or by an electoral miracle. The real transition begins when that network is broken without setting the country ablaze. The challenge is enormous, and it's also a moral one: to unite without vengeance, but without impunity. Targeted justice for those most responsible, truth for the victims, guarantees that the rest will dismantle the system, and a plan for people to live again—not just survive. Because freedom doesn't come with a new president: it comes when the state ceases to be a threat.
January 3, 2026 at 6:16 PM
Reposted by Catherine Clase
edmondsscanner.bsky.social
remember:
a piece of art featuring blue balloons that says "You still haven't met all of the people who are going to love you." Found at Powell's Books in Portland
January 1, 2026 at 5:35 PM
Reposted by Catherine Clase
heathermcpherson.bsky.social
Se réjouir de l’enlèvement illégal d’un chef d’État étranger et célébrer la prise de contrôle d’un autre pays par les États-Unis est irresponsable et dangereux. Le Canada ne peut pas choisir quand le droit international s’applique. Sinon, les règles ne protègent personne.
January 3, 2026 at 6:09 PM
Reposted by Catherine Clase
sujo.bsky.social
In 2026, I'll still be #oneofthetwo because I rely on my health to work & I think everyone should be able to access public spaces as safely as possible.

I'm one of the three when I'm with my family & one of the seven with extended family. There are many people taking infection control seriously.
A photo of a person with chin-length hair and bangs, wearing glasses and a black mask in front of a red neon light thunderbird by Omaskêko Ininiwak artist Duane Linklater.
January 1, 2026 at 1:59 PM
Reposted by Catherine Clase
charleskeener.bsky.social
www.democracynow.org/2026/1/2/hea...
Zohran Mamdani Sworn In as New York’s First Muslim and First Democratic Socialist Mayor
Democratic socialist Zohran Mamdani has been sworn in as New York City mayor. He has made history as New York’s first Muslim, first South Asian and first African-born mayor, and, at the age of 34, the...
www.democracynow.org
January 2, 2026 at 10:47 PM
Reposted by Catherine Clase
thatingrid.bsky.social
COVID-safe on the train
#OneOfTheTwo
January 2, 2026 at 1:34 AM
catherineclase.bsky.social
On now in #Toronto for the next two weeks

#tiff

www.tiff.net/events/the-v...
The Voice of Hind Rajab
Oscar-nominated director Kaouther Ben Hania blends actual recordings and scripted performances to tell the devastating true story of Hind Rajab, a Palestinian girl trapped in a car under Israeli milit...
www.tiff.net
December 29, 2025 at 3:42 PM
Reposted by Catherine Clase
levostregc.bsky.social
The shorteste daye
The longest nighte
Welcome, sun
Welcome, lighte
December 21, 2025 at 6:05 AM
Reposted by Catherine Clase
luckytran.com
Alt text version
Poster in style of Fallout Tv series and game: a person wearing a n95 mask giving a thumbs up on yellow background. Text reads: Safety first! Your future matters. Wear a mask.
December 20, 2025 at 11:28 PM
Reposted by Catherine Clase
mjnabuurs.bsky.social
After the devastating loss of the 3 children in Ottawa, it was urgent to get info out re the additional ways avail to protect one’s loved ones from serious illness as we enter the holidays…

and to remind young fams this amt of sickness ISN’T normal.

#VaccinePlus

ottawa.citynews.ca/2025/12/21/s...
Schools have become cesspools for cold and flu, but they don't have to be: Ontario School Safety
The volunteer organization Ontario School Safety is calling on the provincial government to improve air quality in schools as flu spreads.
ottawa.citynews.ca
December 22, 2025 at 1:59 AM
catherineclase.bsky.social
😮
December 21, 2025 at 5:36 AM
Reposted by Catherine Clase
hswapnil.medsky.social
Food for thought

Science populism, EBM and influencers

absolutelymaybe.plos.org/2025/12/19/s... from @hildabast.bsky.social
Science Populism, Medicine Style - Absolutely Maybe
I hadn’t been aware of the term science populism until a video about it did the rounds recently. It was a light-bulb…
absolutelymaybe.plos.org
December 20, 2025 at 12:01 AM
Reposted by Catherine Clase
esottransplant.bsky.social
Healthcare must never be a target.

ESOT renews its call for humanity and the protection of healthcare in armed conflicts. Patients, healthcare workers, and hospitals are protected under international humanitarian law.

Medical neutrality must be respected.
Humanity must prevail.

[𝘳𝘦𝘢𝘥 𝘮𝘰𝘳𝘦]⤵️
Renewed Call for Humanity and the Protection of Healthcare in Armed Conflicts • ESOT
The European Society for Organ Transplantation (ESOT) reaffirms its mission to protect patients living with, or in need of, life-sustaining therapies for end-stage organ disease, and to uphold the ethical foundations of medical care, regardless of geography, nationality, or political context.
go.esot.org
December 20, 2025 at 8:00 AM
Reposted by Catherine Clase
ajkd.bsky.social
Glucagon-like Peptide-1 Receptor Agonists and Risk of Major Adverse Cardiovascular Events in Patients With CKD

bit.ly/49qlTTE #OpenAccess
December 20, 2025 at 10:01 PM
Reposted by Catherine Clase
mech0t1.bsky.social
An old TTC ad from a while back
December 21, 2025 at 2:02 AM
Reposted by Catherine Clase
aljazeera.com
Winter cold 'becomes lethal' as Israel restricts entry of tents, blankets and other shelter supplies to ravaged enclave https://aje.io/yrvbry
Winter cold 'becomes lethal' as Israel restricts entry of tents, blankets and other shelter supplies to ravaged enclave
December 16, 2025 at 10:30 PM
Reposted by Catherine Clase
cyberciti.biz
Mozilla has a new CEO and he just announced that Firefox will evolve into a modern AI browser. This is a good example of how management doesn’t understand its own user base and why they go out of their way to install Firefox on Windows, Android, iOS and other devices blog.mozilla.org/en/mozilla/l...
A screenshot from the official Mozilla blog that reads: Firefox will grow from a browser into a broader ecosystem of trusted software. Firefox will remain our anchor. It will evolve into a modern AI browser and support a portfolio of new and trusted software additions.
December 16, 2025 at 8:00 PM
Reposted by Catherine Clase
jonathanconp.bsky.social
"Wear a mask if you're sick" stigmatizes those who wear masks.

"Wear a mask if you care about others" is the message that's been missing.
December 15, 2025 at 2:40 PM