Mike Hoerger, PhD MSCR MBA Profile picture
Dec 17, 2022 21 tweets 9 min read Read on X
THREAD: 19 Tips for a DIY mask fit test to reduce your risk of #COVID19.

H/t @amandalhu & @__philipn__

What did I miss? Assorted fit-testing pictures
Fit-testing Tip #1: Keep it Simple.

Get a nebulizer (usually $30-40) & some 3M FT-32 Bitrex solution ($24). The FT-32 fit-test solution (right) goes in the nebulizer. J
Fit-testing Tip #2: Taste the Failure.

Use the nebulizer to spray the bitrex solution (barely visible). Breathe through your mouth. If you taste it, there’s a mask leak.

"It’s not rocket science," as @CorsIAQ likes to say.
Fit-testing Tip #3: Spray at Problem Areas.

I use the nebulizer to spray bitrex fit-testing solution all around the nose bridge, by both cheeks, and under the chin.

You’ll quickly taste a leak. Spray all around the edge of the mask. Make a big loop. Focu
Fit-testing Tip #4: Go Hoodless.

Do what ya wanna, but for DIY fit testing, the method above works fine w/o the hood.

I bought a hood – overpriced! Plus, the goal is to get as many people as possible fit testing. Many would find them off-putting or feel claustrophobic. Me wearing a fit-testing hood. In my view, not needed for DI
Fit-testing Tip #5: Don’t Test around Maskless People/Animals.

After reinstalling a new filter on my Flo Mask, I did a fit test while my son was having a bath. He started coughing. For a moment, I worried he had COVID.

Put 2&2 together, cranked up the HEPA & gave him juice. Don't test around other people or animals. If too much bitre
Fit-testing Tip #6: Have a Beverage Handy.

You’re testing for leaks. You will find some. The bitrex tastes horrible, like licking a rubber band. Have some OJ or a soda ready for after you’re done.
Fit-testing Tip #7: Share the Wealth.

Supplies cost $60 total. It takes hardly any fit-testing solution to test, so offer the opportunity to friends, family, or co-workers. You’ll help protect their health & better cocoon yourself from illness too.

Wise investment. Protect those in your "pods" or "bubbles"
Fit-testing Tip #8: Wear and N95 or #BetterMask.

I tested all 3 of my favorite N95s: the Aegle flat-fold, 3M Aura, and 3M VFlex. I could pass a fit test with each, some caveats noted later. Aegle, 3M Aura, 3M VFlex
Fit-testing Tip #9: Select the Best N95 for YOUR Face.

If you have several masks, test and compare. Go with the winner.

For me, the 3M VFlex held up most robustly. The 3M Aura needs to be readjusted if I talk to much. The Aegle is harder to seal at the nose. The 3M VFlex passed a fit test most easily and robustly, whe
Fit-testing Tip #10: Get your best N95 to fit better.

Although the 3M VFlex most easily & robustly passed fit-testing, I realized I hadn’t been pulling it back far enough under the chin (@jasmith_yorku). I also learned how best to adjust the nose piece to get the best fit. Dr. James showing off how to wear the under-chin region of t
Fit-testing Tip #11: Elastomeric Masks beat N95s.

I tested 6 elastomeric masks. I hate the word “elastomeric.” It’s alienating.

They’re just non-disposable, reusable masks. Great seal. All outperformed my disposable N95s when testing the limits. I'm wearing the Flo Mask, my go-to elastomeric. It's the mos
Fit-testing Tip #12: Get your Elastomeric to Fit Better.

Straps can wear out or loosen over time! Filters also need to be reinstalled properly. Use fit testing periodically and when installing new filters to confirm no leaks. Flo Mask filter. I added a cancer ribbon (safe). Put the fil
Fit-testing Tip #13: Procedure Masks are a Joke.

Fit tested, fails in <0.5 sec. Air flows to the path of least resistance. Gaps poorly guard against inhaling/exhaling viral-laden aerosols.

Everybody should be using #BetterMasks, paid w/public funds.
Fit-testing Tip #14: Cloth Masks are ALSO a Joke.

Also tested a cloth mask. Fails in <0.5 sec. Viral-laden aerosols are too small. Not good enough for 2022.

Everybody should be using #BetterMasks, paid w/public funds.
Fit-testing Tip #15: Fit-test Ear-Loop Masks.

I don't wear ear-loop masks (many KN95/KF94). My experience fit-testing makes me skeptical of cheek gaps.

Worrisome if spending much time in a poorly-ventilated space (car, plane, school, office).
Fit-testing Tip #16: Check for Counterfeits.

Many KN95/KF94 masks are counterfeits, especially on Amazon. Even the city of New Orleans distributed fakes “N95s” last winter. Use fit-testing to check whether a mask is legitimate.
thelensnola.org/2022/01/14/cit…
Fit-testing Tip #17: Facial Hair is a COVID Risk.

My disposable N95s start to fail fit-testing after about 2.5 days w/o shaving. My elastos make it about 3.5 days. If you’re clean-shavin, keep it clean.

If you prefer facial hair, use a mask-safe cut, or know the risk. Facial hair can create mask leaks, increasing COVID risk. Kn
Fit-testing Tip #18: DBAA.

No, fit-testing is not REQUIRED for masks to “work.”

It’s about improving safety on the margins (5-10%) and especially for the most dangerous prolonged contexts.
osha.gov/laws-regs/stan…. https://www.osha.gov/laws-regs/standardinterpretations/2018-
FYI, I have no conflicts of interest, such as investing in one of the companies mentioned.

I’m a psychologist just trying to help people understand COVID mitigation tips I didn’t know a year ago so maybe you can reduce your lifetime number of cumulative SARS-CoV-2 infections.

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More from @michael_hoerger

Jul 2
🌍Want to track COVID transmission accurately worldwide?

This PMC thread walks you through leading dashboards with information more up to date than WHO & EU directories.

🧵 1/ World map, countries with high-quality up-to-date surveillance systems shown in blue.
The Pandemic Mitigation Collaborative (PMC) Dashboard provides weekly COVID updates for the U.S., using wastewater surveillance derived case estimation models and analytic forecasting.

We have added a list of international dashboards:
🧵 2/
pmc19.com/data/index.php…Australia: NSW Health Australia Department of Health, Western Australia Austria: Federal Government of Austria City of Vienna - Regional Coron-A Consortium Austria Czech Republic: State Health Institute Czech Republic Belgium: Belgian Institute for Health Canada: Government of Canada Andrew Young's Canada Visualization C19 Resources Canada * World Health Network (WHN) Canada **
Denmark: Statens Serum Institut Denmark Europe (multi-national): EU Wastewater Observatory Finland: National Institute for Health and Welfare Finland WHN Finland ** France: French Republic Data Airborne Risk Reduction Association (ARRA) France Zan Armstrong's France Visualization COVID Weather App France (Android, IOS, or Web) Thomas Delattre's France Visualization Germany: Infection Radar Germany Bay-VOC Bavaria Region Berlin Waterworks WHN Germany **
Hong Kong: Centre for Health Protection, Hong Kong Hungary: National Center for Public Health and Pharmacy of Hungary India: Pune Knowledge Cluster of India Gujarat Biotechnology Research Centre of India Ireland: Health Protection Surveillance Centre Ireland Japan: Japan Institute for Health Security Latvia: Institute of Food Safety, Animal Health and Environment Latvia Lithuania: National Public Health Centre of Luthuania Luxembourg: Microbs Luxembourg Netherlands: National Institute for Public Health and the Environment Netherlands WHN Netherlands ** New Zealand: New Zealand Institute for...
Slovenia: National Institute of Public Health Slovenia Spain: Government of Catalonia - Regional South Africa: National Institute for Communicable Diseases of South Africa South Korea: Korea Disease Control and Prevention Agency Sweden: Pathogens Sweden Switzerland: Swiss Confederation Federal Office of Public Health ETH Zurich Switzerland WISE Dashboard U.K.: Public Health Scotland Buckinghamshire Disability Service (BuDS) U.K.  *See the numbers 1-21 along the lower left. Click on 3-6 for national and regional data. ** Click on the dropdown menu. May need to try a different web browser.
Our international directory includes official government dashboards & those developed by citizen scientists.

We exclude countries that have stopped reporting in the past 2-12 months even if on EU or WHO lists. We also exclude low-quality data from opt-in testing programs.
🧵 3/
Read 43 tweets
Jun 24
PMC COVlD Dashboard, Jun 23, 2025 (U.S.)

🔥Biggest uptick since Jan
🔥1 in 167 actively infectious
🔥>2 million weekly infections
🔥700-1,200 resulting excess deaths from weekly infections

Track transmission closer to home w/our new state & international resources 👇

🧵1/6
PMC COVlD Dashboard, Jun 23, 2025 (U.S.)

🔹With >90% probability, we have entered the 11th COVlD wave.
🔹In a room of 50 people, there is already a 1 in 4 chance of an exposure.
🔹We expect nearly 15 million infections in the next month, and rising.

🧵2/6Current Levels for Jun 23, 2025	 % of the Population Infectious	 0.6% (1 in 167)	 New Daily Infections	 287000	 New Weekly Infections	 2009000	 Resulting Weekly Long COVID Cases	 100,000 to 402,000	 Resulting Weekly Excess Deaths	 700 to 1,200	 	 Monthly Forecast	 Average % of the Population Infectious	 1.0% (1 in 97)	 Average New Daily Infections	 493300	 New Infections During the Next Month	 14799000	 Resulting Monthly Long COVID Cases	 740,000 to 2,960,000	 Resulting Monthly Excess Deaths	 5,300 to 8,800	 	 Running Totals	 Infections Nationwide in 2025	 74869000	 Average Number of Infect...
PMC COVlD Dashboard, Jun 23, 2025 (U.S.)

We continue to expect transmission to break 500,000 daily infections in the U.S. around July 9th.

This is the same prediction as last week, as the forecast was dead on. Yet, there is considerably uncertainty around this timing.

🧵3/6Longitudinal transmission, past 12 months and 1-month forecast
Read 6 tweets
Jun 17
1) PMC COVlD Dashboard, June 16, 2025 (U.S.)

Current transmission (red line) closely tracks that of summer 2023 (yellow line).

We expect to break 500k daily infections between July 9 and the end of July. Our current forecast...Year over year graph of tranmission
2) PMC COVlD Dashboard, June 16, 2025 (U.S.)

Our current forecast is a bit more aggressive, predicting breaking 500k daily infections by July 9. The 2023 trend suggests end of July.

The 95% confidence interval shows large variation. Note that...Past 12 months of transmission (U.S.) and forecast
3) PMC COVlD Dashboard, June 16, 2025 (U.S.)

Note that CDC and Biobot both had retroactive corrections to last week's data, meaning the relative "lull" will last a little longer than the uncorrected data suggested. No big news on NB.1.8.1.

All good news, but...10 pandemic waves. Soon 11
Read 7 tweets
Jun 16
1) Here's a quick example of how the federal government is censoring the best scientific research. It's not just cuts to ongoing research.

It's new grant submissions too... "No forbidden words found"
2) In January, I re-submitted a promising Covid/cancer grant to a non-federal funder. Hundreds of pages. Hundreds of hours of work. The best proposal I've submitted as a scientist.

Out of curiosity, I used Sean Mullen's Scan Assist tool to see how many banned words it had...
3) The proposal had 1,750 banned words. No big deal -- they're non-federal.

BUT I had planned to submit a smaller version to NIH this month as a "back up." Impossible!

It's not a matter of using a thesaurus or the find/replace command. The grant is on *Covid*... 1,750 banned words found
Read 13 tweets
Jun 9
1) PMC COVlD Dashboard, June 9, 2025

CDC wastewater surveillance data show transmission rising. This is our forecast if transmission growth follows typical patterns.

The high & low estimates could be thought of as optimistic & pessimistic scenarios for NB.1.8.1.Forecast graph: Rising transmission the next month
2) PMC COVlD Dashboard, June 9, 2025

Notice that current transmission (red line, lower left) tracks closely with two years ago (yellow), slightly below the median (gray), and not far below last year (orange).

Consider each of these trajectories realistic scenarios.Image
3) PMC COVlD Dashboard, June 9, 2025

All indications are that we are headed into the start of an 11th national wave in the U.S.

We could percolate near the lull point another couple weeks (fingers crossed), but that scenario is becoming less likely.Graph of 10 C19 waves
Read 7 tweets
Jun 3
1/ PMC COVlD Dashboard, June 2, 2025 (U.S.)

National COVlD transmission recently fell to its lowest levels since the pre-Delta era.

It's go-time for many who have delayed medical appointments. The situation will likely get much worse in Jul/Aug.
2/ PMC COVlD Dashboard, June 2, 2025 (U.S.)

An estimated 1 in 211 are actively infectious. Most states are "low" or "very low" per CDC.

The situation remains serious even in a relative "lull." >1.5 million weekly estimated infections to result in 600-900 excess deaths.C19 heat map
year over year graph, tracking closely with the median and past 2 years
Current Levels for Jun 2, 2025	 % of the Population Infectious	 0.5% (1 in 211)	 New Daily Infections	 227000	 New Weekly Infections	 1589000	 Resulting Weekly Long COVID Cases	 79,000 to 318,000	 Resulting Weekly Excess Deaths	 600 to 900	 	 Monthly Forecast	 Average % of the Population Infectious	 0.7% (1 in 139)	 Average New Daily Infections	 344566.6667	 New Infections During the Next Month	 10337000	 Resulting Monthly Long COVID Cases	 517,000 to 2,067,000	 Resulting Monthly Excess Deaths	 3,700 to 6,200	 	 Running Totals	 Infections Nationwide in 2025	 70132000	 Average Number of Infe...
Graph of the whole pandemic, 11th wave forthcoming
3/ PMC COVlD Dashboard, June 2, 2025 (U.S.)

By the end of the month, we forecast an increase to 450k daily infections. If NB.1.8.1 takes off, closer to 600k. If overhyped, percolating only slightly higher.Past 12 months and forecast
Read 5 tweets

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