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

Aug 21
During times like these when COVlD transmission heats up in the U.S., expect to see a lot more angry outbursts for three central reasons.

First, "displacement," or people trying to deny the reality of their anxiety by taking it out on other people....
Second, a lot of people can sustain a strong denial of reality about the ongoing pandemic during lulls. They suppress the existence of COVlD waves and excess deaths, disability, and retirements.

During waves, those defenses burst. Loss of control = anger...
Third, a lot of people (many reading this) understand COVlD correctly & experience righteous indignation during COVlD waves. We quite reasonably do not like all of the unjust and gratuitous suffering.

I find it helpful to channel that intensity into helping other people....
Read 6 tweets
Aug 19
I submitted my comment to endorse universal high-quality masks (respirators) in healthcare. Today is the final day.

Alt text continues in the following posts. RE: Z94.4, Selection, use, and care of respirators (New Edition)  Dear Colleagues,  As the director of a population science program at a major U.S. cancer center, I strongly endorse this draft proposal to increase the use of high-quality well-fitting masks (respirators) in medical settings. I will comment on the relevance of this proposal mainly for cancer care. In the U.S., cancer care is commonly more organized than other specialty care and, thus, often leads the way on policy initiatives, which then translate to other elements of care over time.  1. COVID-19 continues to cause excess dea...
They put forth projections, with the most granular detail for the U.S. and U.K., suggesting excess deaths will persist through at least 2033. Their projections do not show excess deaths stopping in 2033; that is simply the final year of their current analysis. Moreover, while they provide the most data for the U.S. and U.K., their analysis suggests a more general trend throughout the globe. The COVID-19-associated excess deaths are commonly identified as cardiovascular and cancer causes of death.   Swiss Re Institute. (2024). The future of excess mortality after COVID-19. https://www.swissr...
Alt text continued 2. The SARS-CoV-2 virus that causes COVID-19 continues to transmit at high rates worldwide. Overall, 28 nations continue to use wastewater surveillance to monitor SARS-CoV-2 levels. A directory is available at the dashboard that I oversee (pmc19.com/data). In the U.S., we are currently experiencing our 11th wave of transmission. Many nations are experiencing annual or twice annual waves of transmission.
Alt text continued 3. International consensus standards identify a broad range of patients at known high-risk of severe outcomes of COVID-19. The largest group at known high risk of severe outcomes is patients with cancer. Other diagnoses associated with above average risk include people undergoing transplants or receiving dialysis, and patients with any of these diagnoses: immunodeficiencies, renal disease, systemic-immune mediated or single-site immune-mediated inflammatory conditions, asplenia, anatomical barrier defects, pregnancy, and diabetes. These findings underscore the importance of standards in hea...
Read 7 tweets
Aug 16
🚩🚩🚩
As a vigorous defender of #CDC data, their switch from using normalized to non-normalized COVlD wastewater surveillance data today harms data quality.

"Normalizing" means accounting for basic confounders like rain levels. It is a choice to use worse data.
1/5🧵 Image
Historically, the CDC data have correlated near-perfectly with similar metrics, such as Biobot's wastewater estimates (still active) or the IHME true case estimates (through mid-2023).

The changes reduce those correlations. It's like going from an A+ to a B.

2/5🧵
You can readily see the loss of data quality in the PMC "whole pandemic" graph (preview shown, subject to change) with choppier waves, caused by the CDC adding extra noise to the data and applying retroactively from BA.1 Omicron to present.

3/5🧵 Longitudinal graph of the pandemic waves. Notice how they start becoming choppier in 2022, as a result of today's changes at the CDC
Read 5 tweets
Aug 12
PMC COVID Dashboard, August 11, 2025 (U.S.)

The CDC says transmission is heating up.

"Very High" (3)
🔺Guam
🔺Hawai'i
🔺Louisiana

"High" (12)
🔺Alabama
🔺Alaska
🔺California
🔺Colorado
🔺Delaware
🔺Florida
🔺Indiana
🔺Mississippi
🔺Nevada
🔺S. Carolina
🔺Texas
🔺Utah

🧵1/12Heat map from CDC data. High/Very high states noted in post
Transmission is highest in these regions. Graphics note the CDC levels and PMC prevalence estimates.

🔥Louisiana (Very High): 1 in 19 actively infectious
🔥Guam (Very High): 1 in 26
🔥Hawai'i (Very High): 1 in 28
🔥Texas (High): 1 in 45

🧵2/12 Graphics show heat maps and prevalence estimates, noted in the post
Statewide transmission remains "High" in Florida, according to the CDC. PMC estimates 1 in 50 actively infectious.

Several cities report "Very High" transmission. Several sites are offline.

🧵3/12 Heat map and prevalence estimate noted in the post
Read 12 tweets
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

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