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 29
PMC COVID Dashboard, July 28, 2025 (U.S.)
🧵1/12

PMC estimates 400,000 new daily infections. 1 in 118 people actively infectious.

Weekly stats:
🔹2.8 million infections (>40x reported cases)
🔹>140,000 resulting #LongCOVID cases
🔹>1,000 resulting excess deaths Heat map Very High: Louisiana, Guam High: Hawai'i, Florida
PMC COVID Dashboard, July 28, 2025 (U.S.)
🧵2/12

Please excuse any typos and delays. Any time Mimal's boot turns deep red, we're doing local outreach in addition to dashboard work, etc.

If you don't know Mimal yet, you won't be able to unsee them.
es.wikipedia.org/wiki/MIMALDeep red boot = Louisiana
Minnesota (M), Iowa (I), Missouri (M), Arkansas (A), Louisiana (L) = Mimal  Louisiana is the boot.   Sometimes depicted with Kentucky fried chicken on a Tennessee pan.
PMC COVID Dashboard, July 28, 2025 (U.S.)
🧵3/12

It's HOT COVID SUMMER in the Deep South. No geographic/political prejudices, see next.

Covid is burning through Guam, Louisiana, Florida, and Texas (underestimate due to sites down). Louisiana: 1 in 32, Very High (CDC)
Texas: 1 in 98, Moderate (underestimate, CDC)
Guam: 1 in 25, Very High (CDC)
Florida: 1 in 59, High (CDC)
Read 12 tweets
Jul 25
U.S. CDC numbers just released. Good news (for those not in Louisiana). "Only" a 5% national increase.

2025 has closely tracked with summer 2023 transmission. A 12-13% increase would have been expected based on those numbers. That said... Up: Midwest, Northeast Down: West, South
real-time data have been prone to retroactive corrections. This is frustrating, of course, because it leaves people making decisions based on data that are only of good quality when 2 weeks old.

If we saw a 12% increase this week, I'd say look at 2023 for a glimpse...
at the future. Instead, I would consider these plausible scenarios:
🔹Wave still similar to 2023
🔹Later wave with schools more implicated
🔹Something temporarily much better

Of course, temporarily better often means...
Read 6 tweets
Jul 21
1. PMC COVlD Dashboard, July 21, 2025 (U.S.)

COVlD is surging in 7 states, according to the CDC.
🔹Hawai'i (Very High)
🔹California (High)
🔹Nevada (High)
🔹Texas (High)
🔹Louisiana (High)
🔹Florida (High)
🔹South Carolina (High) Heat map, summarized in post
2. PMC COVlD Dashboard, July 21, 2025 (U.S.)

Western surge:
🔹California: 1 in 63 actively infectious, much higher in LA & Bay areas
🔹Hawai'i: 1 in 35 actively infectious
🔹Nevada: 1 in 63 actively infectious

These are wastewater derived estimates, not from individual tests CA map with stat summarized in post
NV  map with stat summarized in post
HI  map with stat summarized in post
3. PMC COVlD Dashboard, July 21, 2025 (U.S.)

Southern surge:

🔹Texas: 1 in 56
🔹Louisiana (New Orleans): 1 in 65
🔹Florida: 1 in 66
🔹South Carolina: 1 in 71

Again, wastewater estimates (wise indicator), not individual testing (low-quality data). SC map and stat noted in post
LA map and stat noted in post
FL map and stat noted in post
TX map and stat noted in post
Read 12 tweets
Jul 15
1) PMC COVlD Dashboard, July 14, 2025 (U.S.) 🧵

We estimate 1 in 148 Americans are actively infectious. This equates to 2.3 million infections/week, expected to result in >100,000 new #LongCOVID conditions & >800 deaths.

A room of 100 people is a coin toss of an exposure. Figure shows each wave of the pandemic.   Tables: Current Levels for Jul 14, 2025	 % of the Population Infectious	 0.7% (1 in 148)	 New Daily Infections	 324000	 New Weekly Infections	 2268000	 Resulting Weekly Long COVID Cases	 113,000 to 454,000	 Resulting Weekly Excess Deaths	 800 to 1,300	 	 Monthly Forecast	 Average % of the Population Infectious	 1.3% (1 in 80)	 Average New Daily Infections	 598766.6667	 New Infections During the Next Month	 17963000	 Resulting Monthly Long COVID Cases	 898,000 to 3,593,000	 Resulting Monthly Excess Deaths	 6,400 to 10,700	 	 Running Totals	 Infection...
2) PMC COVlD Dashboard, July 14, 2025 (U.S.) 🧵

Transmission (red) is closely tracking the path of 2 years ago (yellow). However, the incoming data are spotty. >20% of CDC states have limited/no data, & Biobot hasn't reported in weeks.

Could be MUCH worse or slightly better. Graph of year over year transmission. The current year (red) is tracking the path of two years ago (yellow) extremely closely. Two years ago, the peak was around September 1, at about 1 million daily estimated infections, and significantly higher than the Delta wave (blue).
3) PMC COVlD Dashboard, July 14, 2025 (U.S.) 🧵

Our model formalizes the mathematical assumptions in those predictions. If transmission follows what we know in terms of how waves grow or slow generally and historical patterns, this is what we'd expect.

The spottiness of the current real-time data reduce precision substantially. Retroactive corrections can make the forecast jump around from better to worse from one week to the next. Expect the worst. Hope for the best.Graph shows national transmission expected to increase the next several weeks.
Read 11 tweets
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

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