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

Nov 3
PMC COVlD Update, Nov 3, 2025 (U.S.)
1 of 9 🧵

The relative "lull" in SARS-CoV-2 transmission is unlikely to go much lower.

✨1 in 209 people are estimated actively infectious, likely the lowest levels of 2025 nationwide.

Get boosted. Stock up on masks, tests, & filters. Year-over-year graph
PMC COVlD Update, Nov 3, 2025 (U.S.)
2 of 9 🧵

No data presently suggest the rise of a winter wave any earlier than "usual."

If following historical trends, transmission will pick up Nov 15-29. Last year's rise was atypically late. Forecasted transmission
PMC COVlD Update, Nov 3, 2025 (U.S.)
3 of 9 🧵

Expect rising misinformation/disinformation as transmission heats up:
🔹Abuse of community notes, particularly surrounding wastewater methodology
🔹Paid bot army attacks, especially about boosters & masks
Read 9 tweets
Oct 28
PMC COVlD Update, Oct 27, 2025 (US)

Transmission typically accelerates in mid-November.

We are currently in a relative 'lull.' We estimate about a quarter-million new daily infections with 1 in 185 people actively infectious. Still bad, likely to get worse.

1/9 🧵 year over year graph
PMC COVlD Update, Oct 27, 2025 (US)

Our forecast through November 8 calls for flat transmission.

Nothing yet indicates the onset of a winter wave, but it would also be atypical for the lull to last much longer than another 2-3 weeks.

2/9 🧵 Graph of recent transmission and current forecast
PMC COVlD Update, Oct 27, 2025 (US)

We estimate 264,000 new daily infections during this 'lull' period.

Biobot data have returned. Our substitute data from WWS last week correlated r=.97 (near perfect) with that, but Biobot did retroactively increase recent estimates.

3/9 🧵 Graph of the 11 waves of the pandemic
Read 9 tweets
Oct 21
PMC COVlD Update, Oct 20, 2025 (U.S.)

SARS-CoV-2 transmission has fallen.
🔹1 in 191 (0.5%) actively infectious
🔹"Lull" levels at 20% of the summer peak
🔹255,000 new daily infections (still concerning)

Many will knock out higher-risk activities the next 2-4 weeks.
🧵1/11 Graph of the 11 waves, shows current lull.
PMC COVlD Update, Oct 20, 2025 (U.S.)

"Lull" transmission remains dangerous:
🔹1.8 million estimated new weekly infections
🔹>90,000 estimated new #LongCOVID conditions from this week's infections
🔹>500 excess deaths to result from this week's infections

🧵2/11 Infections						 Proportion Actively Infectious										1 in 191 (0.5%) New Daily Infections										 255,000  Infections the Past Week										 1,800,000  Infections in 2025										 191,000,000  Cumulative Infections per Person										 4.69  										 Long COVID										 Long COVID Cases Resulting								13,000 to 51,000		   from New Daily Infections										 Long COVID Cases Resulting								90,000 to 360,000		   from New Weekly Infections										 										 Excess Deaths										 Excess Deaths Resulting 									70 to 120	   from New Daily Infections										 Excess Deaths ...
PMC COVlD Update, Oct 20, 2025 (U.S.)

Exposure risk during "lull" transmission remains high when engaging in many social interactions.

Interacting with 25 people yields a 12% chance of exposure. 100 people? 41% chance of exposure, assuming no testing/isolation.

🧵3/11 Number of People		Chances Anyone is Infectious		 1				0.5% 2				1.0% 3				1.6% 4				2.1% 5				2.6% 10				5.1% 15				7.6% 20				10.0% 25				12.3% 30				14.5% 50				23.1% 75				32.5% 100				40.8% 200				64.9% 300				79.2%
Read 11 tweets
Oct 11
PMC COVlD Wave Update (Europe)
11 October 2025 🧵

The PMC website includes an international directory of websites with COVlD wastewater monitoring. It is more up to date than the directories of the EU and WHO.

Let's review what's happening in Europe...

1/ world map, nations with surveillance shown in blue. URL says pmc19.com/global
Data in #Austria show a rising COVlD wave. The x axis (bottom) has infrequent labels, but the data shown go through October 8th.

Find more here:

2/ pmc19.com/austrialongitudinal graph
COVlD levels have been percolating in #Belgium, with "moderate" levels overall.

The transmission pattern is similar across regions. Plants at Namur-Brumagne and Oostende report "high" levels.



3/ pmc19.com/belgiumheat map and longitudinal graph
Read 20 tweets
Oct 5
PMC COVlD Update, Week of Oct 6, 2025 (U.S.)
🧵1/9

An estimated 1 in 81 people are actively infectious during the ongoing 11th wave.

The "shutdown" has created a blackout at the state level.

Transmission is half that of the peak one month ago, and we anticipate a relative national "lull" in early-to-mid November, albeit still at dangerous levels.

Our model uses a combination of CDC and Biobot data, so we are able to estimate national statistics despite the CDC data going offline. On the map, note that Puerto Rico continues to update; they use a CDC-style system but were dropped by the CDC long ago. For full methodology, review the technical appendix on the website.Heat map, grayed out. 1 in 81 estimated actively infectious, or 602,000 new daily infections, per wastewater-derived estimates.
PMC COVlD Update, Week of Oct 6, 2025 (U.S.)
🧵2/9

#DuringCOVID is today. We estimate >600,000 new daily infections. This is about half the peak on September 6.

Notice current levels are similar to the estimated peaks of the first 3 waves. 11 wave graph
PMC COVlD Update, Week of Oct 6, 2025 (U.S.)
🧵3/9

Weekly estimates:
🔹4.5 million infections
🔹>200,000 resulting long-term health conditions
🔹>1,300 resulting excess deaths Infections						Oct 6, 2025				pmc19.com/data Proportion Actively Infectious										1 in 81 (1.2%) New Daily Infections										 602,000  Infections the Past Week										 4,540,000  Infections in 2025										 189,000,000  Cumulative Infections per Person										 4.69  										 Long COVID										 Long COVID Cases Resulting								30,000 to 120,000		   from New Daily Infections										 Long COVID Cases Resulting								227,000 to 910,000		   from New Weekly Infections										 										 Excess Deaths										 Excess Deaths Resulting 									170 to 280	   from New Daily Infe...
Read 9 tweets
Oct 3
BREAKING: 3 State Pharmacy Boards Still Block COVlD Boosters without a Prescription

ACIP voted against prescriptions for boosters & 47 states + DC follow that guidance.

Georgia, Missouri, & Louisiana require prescriptions.

Key points in my letter to the pharmacy boards. 🧵1/7 Map shows only Missouri, Louisiana, and Georgia are blocking residents from routing COVlD boosters unless they have a prescription.
Georgia law indicates that the pharmacy board is to follow ACIP. They do not dictate further nuance. Georgia continues to require prescriptions, going against the spirit of the law, ACIP, and 47 other states.

🧵2/7 Georgia:  State law does NOT require a prescription if it is a “vaccine that is included on the adult immunization schedule recommended by the Advisory Committee on Immunization Practices (ACIP)”1 ACIP voted against prescriptions, and 47 states have accepted that schedule.  The law does not mention a CDC Director sign-off, which may be delayed months. Act now to save lives.  1. https://law.justia.com/codes/georgia/title-43/chapter-34/article-2/section-43-34-26-1/
Louisiana law tells the pharmacy board to follow ACIP. ACIP says do not require a prescription, and 47 other states agree.

The Louisiana pharmacy board continues to require a prescription.

🧵3/7 Louisiana:  State law does NOT require a prescription if the “vaccine is administered in conformance with the most current immunization administration protocol as set forth by the United States Centers for Disease Control and Prevention Advisory Committee on Immunization Practice.” 2 ACIP voted against prescriptions, and 47 states have accepted that protocol.  The law does not mention a CDC Director sign-off, which may be delayed months. Act now to save lives.  2. https://law.justia.com/codes/louisiana/revised-statutes/title-37/rs-37-1218-1/
Read 7 tweets

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