THREAD: 19 Tips for a DIY mask fit test to reduce your risk of #COVID19.
H/t @amandalhu & @__philipn__
What did I miss?
Fit-testing Tip #1: Keep it Simple.
Get a nebulizer (usually $30-40) & some 3M FT-32 Bitrex solution ($24).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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….
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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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/
Data in #Austria show a rising COVlD wave. The x axis (bottom) has infrequent labels, but the data shown go through October 8th.
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.
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.
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
Key points in my letter to the pharmacy boards. 🧵1/7
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
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.
On the back end of this unprecedented 11th wave, "times they are a-changin." In particular, COVlD levels are shifting north and east.
Notice that few states are in the highest and lowest categories. Much of the south and west have considerable transmission post-peak. Many places in the north and east are seeing steady or increasing transmission after relatively lower levels.
Overall, levels are lower than the past few weeks, but transmission remains considerable. Those relying on anecdata (friends, coworkers, and family infected) may increasingly realize we are in a wave.
We estimate nearly 750,000 new daily infections nationwide, meaning approximately 1 in 66 people or 1.5% are actively infectious.
These estimates are derived by linking wastewater levels to IHME true case estimates using methodology commonly employed worldwide, detailed on the website, noted in a pre-print. Many publications in leading medical journals link wastewater data to key metrics that matter, noted in the online technical appendix.
In this week's report, we note adding North Dakota and Puerto Rico to the heat map in support of health equity. We have been imputing ND levels since the launch of PMC 3.0 using data from neighboring states. PR continues to report qualitative levels using the CDC format but is not longer included on the CDC website.
1/8 🧵
PMC COVlD Update, Sep 29, 2025 (U.S.)
State-level prevalence estimates, AL to MS. The levels use CDC labels, which tend to have an optimistic portrayal of risk. For example, CO is listed at "low" (by our estimate 1.5% infectious).
#MaskUp at 1.5% if having lapsed.
2/8 🧵
PMC COVlD Update, Sep 29, 2025 (U.S.)
State-level prevalence estimates, Missouri to Wyoming.
New York had *huge* retroactive upward corrections, and is now "High," as many residents hypothesized.
Note, Puerto Rico only provides CDC qualitative levels, so no data.