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Dr. Alex Huffman Profile picture
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5 Feb, 33 tweets, 25 min read
1/ In context of extra precautions against new COVID variants, some new questions pop up about #masks.

Article by @cwarzel @zeynep asks/answers some good questions to start. Other thoughts in a 🧵, e.g. N95s, fit (Tw7+ ⬇️), when to replace (Tw25 ⬇️), etc.
nytimes.com/2021/01/29/opi…
2/ Countless recent articles w/ interviews from relevant experts imploring people to still take mask-wearing & overall airborne COVID health seriously.

One of many, here by @skbaer w/ broad contribution. (Tw33 below has link to a compilation of more).
buzzfeednews.com/article/skbaer…
3/ Many good arguments recently towards motivating broader use of #bettermasks, i.e. #N95s. So if not using already, consider.

See e.g. this editorial by @j_g_allen: washingtonpost.com/opinions/2021/…

Or this opinion-piece by a group of excellent scientists:
4/ One of the simplest overviews on practical aspects of this topic of upgraded masks/respirators (i.e. N95s, KN95s, double-masking) is a brief video interview also with @j_g_allen:
5/ Also a great overview on the importance & physical science principles behind face masks for COVID-19 protection was written recently by @MonicaGandhi9 & @linseymarr. It's a very short, easy read; worth your time.
cell.com/med/fulltext/S…
6/ This is one of the best videos to explain how masks work (especially focused on #N95s); by @minutephysics.
7/ To achieve adequate health benefit from masks, keep in mind that both FILTRATION & FIT are critical.

I frequently share this video that beautifully demonstrates the importance of fit. Notice what happens to the aerosol with a poorly fitting mask:
8/ Scientific motivation for better mask FIT quality is deep & wide. Three of *many*:

I.e. poor fit of surgical masks = insufficient & danger to HCWs

Goldberg et al:
Prof. @CappaSnappa: researchsquare.com/article/rs-142…
Rothamer et al (⬇️): medrxiv.org/content/10.110…
9/ Also *lots* of research & resources on mask/filtration quality. 🧵 not meant to be comprehensive, but e.g.:

Pan et al: medrxiv.org/content/10.110…
Clapp et al: jamanetwork.com/journals/jamai…
Interactive graphs by @smogdr: jv.colostate.edu/masktesting/
Lit: examine.com/topics/coronav…
10/ One strategy to improve filtration/fit combo could be to double-mask. This can be effective (webinar from Sept by @Smogdr w/ test data: ).

But make sure that the added layers don't interfere with your ability to breath smoothly through the material.
11/ Another broad strategy to improve mask FIT is to add a #maskbrace to hold on a looser mask w/ gaps (i.e. surgical). It's usually a piece of rubber that makes sure no aerosol sneaks in or out through gaps at your face, nose, chin.

E.g. Rothamer et al.: medrxiv.org/content/10.110…
12/ Here is a short video interview with @katherinepasem1, a designer of the @FixTheMask brace:

You can buy these braces at fixthemask.com.
13/ OR you can use the free template provided by @FixTheMask to make your own #maskbrace for improved fit.
fixthemask.com/products/v2-di…
14/ This is a nice video explaining by @FixTheMask filtration in general and the importance of good mask fit:
15/ @linseymarr (aerosol & mask-testing expert) recently shared her impressions after having made one of these DIY mask braces:
16/ Another good #maskbrace option is the Badger Seal developed through @UWMadEngr, which can be purchased for ~$10 or made yourself using their linked instructions & videos.
making.engr.wisc.edu/mask-fitter/
17/ No matter the mask, only as effective as it's ability to seal to face around both nose & mouth.

If hard to breath through a #mask, it is too restrictive/thick. Air (& aerosol) will always escape mask. If air exits via gaps rather than THROUGH layer(s), mask is ineffective!
18/ CDC doc gives some tips related to checking the seal of your mask/respirator:

- Make sure material sucks in or blows out sufficiently when breathing
- Fogging glasses or gaps formed are signs of poor fit

(Note: for COVID, never use a mask w/ valve!)
cdc.gov/niosh/docs/201…
19/ This is a 4-min video also shows how to do a user seal-check on a #N95 mask/respirator.

Keep in mind that this was developed for occupational safety and not wrt general public health, but most principles still apply.

(HT @DavidLKeating)
20/ Some other links with various tips & hacks in terms of mask fit:

Via @NebraskaMed: nebraskamed.com/COVID/13-mask-…

O'Kelly et al: medrxiv.org/content/10.110…

CDC: cdc.gov/coronavirus/20…

Via @lisa_iannattone:

Article by @mgodoyh: npr.org/sections/healt…
21/ Also important to note that facial hair/beards makes it very difficult/impossible to get a good fit to your face and so efficiency of the #mask is reduced.

Check out this awesome CDC/NIOSH chart.

Be a #walrus, not Dali!
cdc.gov/niosh/npptl/pd…
22/ Related; you have probably heard of the "#candletest" for testing filtration quality (i.e. blow through mask; candle flame out = bad). I personally don't like this, b/c may just mean air/aerosol escapes through gaps. E.g.:

npr.org/sections/goats…
23/ Mid-summary: Upgrade to best mask quality you can find (N95 if avail., KF94, possibly KN95), but FIT is always still critical. #bettermasks

If you can't breathe easily so exhaled breath goes THROUGH material, it is too restrictive and/or a bad fit.
24/ One concern is counterfeit or knock-off #N95, #KN95 respirators. I don’t think anything is fool-proof, but the CDC has this resource:
cdc.gov/niosh/npptl/us…
25/ Another question that has come up a lot recently is how long you can wear your #N95-type mask. See tweet #1 for some ideas & sub-links.

First, if possible look at manufacturer recommendations for tips.

CDC/NIOSH officially lists e.g. 8-hr limit: cdc.gov/niosh/topics/h…
26/ The next set of tweets is NOT meant to be definitive, b/c there are plenty of people who work in this space more than I do. I assembled some thoughts related to practical questions, however, and these may be helpful as you answer questions specific to your situation.
27/ Convos about practical N95 care & longevity, w/ @linseymarr @Smogdr @j_g_allen @JudahWorldChamp +

- Rotate use per day:
- Filtration likely good for months:
- Good until straps no longer pull to seal:
28/ A few add’l #N95 tips:

- Use longer than 8-hrs likely ok if necessary:
- But best to swap when damp from use (can reduce filtration)
- N95, HEPA filtration add electrostatic properties to boost filtration; this is reduced when damp or after washing
29/ For use outside of a medical environment, it is probably best not to clean N95s but rather to rotate use. I.e. place aside in a paper bag for a couple days and then return, e.g. suggestion by @smogdr:
30/ In a medical environment, may be necessary to sterilize if not enough to dispose. Several studies have focused on break-down after rounds of cleaning, e.g.:

generalsurgerynews.com/In-the-News/Ar…

pubmed.ncbi.nlm.nih.gov/33279587/

Via @linseymarr:
31/ One question is about shelf-life of N95 (and similar) masks. That is relatively little concern. They don't physically break down easily.

This study also supported that from an experimental perspective:
aaqr.org/articles/aaqr-…
32/ Summary: Masks still a critical piece of community armor against further COVID transmission. As variants of concern threaten, upgrade to #bettermasks & focus on fit.

For more general answers wrt #COVIDisAirborne, see FAQ by @jljcolorado & colleagues: tinyurl.com/FAQ-aerosols
33/ If you want to read still further about #bettermasks and much more, lots of articles (search "mask") compiled on both 'media' tab (i.e. news) & 'science articles' tab (research).
docs.google.com/spreadsheets/d…

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More from @HuffmanLabDU

Dr. Alex Huffman Profile picture
3 Feb
1/ Public admission by @mvankerkhove of #WHO that COVID transmission "goes through the air" is a *huge* turn-around from strong, incorrect statements to the contrary.

Strikes me as significant, even if subtle & played off as "we knew all along."

Full vid
2/ Earlier messages #WHO put out were blatantly wrong & dangerous ⬇️.

Many scientists globally have been working tirelessly to pressure @WHO to retract dangerously misleading statements like this & adequately educate that #COVIDisAirborne.
3/ Again, messaging efforts by WHO are critical b/c of their exposure & reach. By openly saying COVID isn't in the air & having press conferences w/o masks, have been undermining efforts to #MaskUp & prevent spread.

Baby steps today, still work to do!
Read 7 tweets
Dr. Alex Huffman Profile picture
3 Feb
Updated preprint on COVID risk modeled from respiratory aerosol data

Notice ⬇️:
- No "safe" distance indoors, b/c aerosols travel
- Masks & ventilation increase safe time, but still risk

Graphs: below each line = safer

HT @linseymarr & @kprather88 (1/x)
medrxiv.org/content/10.110…
2/ Study used the #WellsRiley model to estimate COVID risk from respiratory aerosols in a variety of scenarios, using particle size distribution data from previous studies.

Quanta: Statistical measure of avg infection probability; bigger value = easier to infect [~1 - e^-quanta]
3/ Bazant & Bush study supports broad consensus of observation & preventative steps:

✅No single action sufficient for COVID prevention
✅Steps compound reduction in risk, but never to zero
✅All important: distance, masks, reduced time, incr. ventilation
medrxiv.org/content/10.110…
Read 6 tweets
Dr. Alex Huffman Profile picture
1 Feb
Imp. perspective to remember.

"Excessive attention on making surfaces pristine takes up limited time & resources that would be better spent on ventilation or the decontamination of the air that people breathe": @linseymarr

By @dyanilewis HT @rye_b (1/x)
nature.com/articles/d4158…
2/ A few other key quotes/reminders:
“It’s become clear that transmission by inhalation of aerosols — the microscopic droplets — is an important if not dominant mode of transmission,” says Prof. @linseymarr , who studies airborne disease transmission.
3/
 “You have to make up some really convoluted scenarios in order to explain superspreading events w/ contam. surfaces”
“If we’ve already paid attention to the air & we have some extra time resources, then yes, wiping down those high-touch surfaces could be helpful”: @linseymarr
Read 5 tweets
Dr. Alex Huffman Profile picture
30 Jan
Study showing nosocomial (in hospital) transmission of COVID to HCWs despite surgical masks & distancing.

Important b/c:
1) Virus aerosolized w/o AGPs; only possible if airborne
2) Surgical masks insufficient (weak filtration; bad leakage)
via @CPita3 1/x
academic.oup.com/ofid/advance-a…
2/ Conclusions of the study are anecdotal, but they are important b/c they add further direct support to a mountain of diverse evidence suggesting #COVIDisAirborne, though not treated so by #WHO and others.

RT original from @CPita3:
3/ One key, practical take-away: upgrade your #mask quality (#N95, when possible) and always make sure it fits snugly all around to reduce air/virus leakage & transmission risk.
Read 6 tweets
Dr. Alex Huffman Profile picture
28 Jan
My heart is heavy today at the loss of Prof. Paul Crutzen, Nobel Laureate and a giant of both science & humanity, truly with no equal.

So many profound contributions: ozone layer chemistry, nuclear winter, #Anthropocene, +

A few quotes & obs. below (1/x)
mpic.de/4677594/trauer…
2/ "He was the first to show how human activities damage the ozone layer. This knowledge ... was the basis for the worldwide ban on ozone-depleting substances – a hitherto unique example of how Nobel Prize-winning basic research can directly lead to a global political decision.”
3/ “Paul Crutzen was also a pioneer of the sciences focusing on the impact of human civilization on the environment, whether through his findings on the destruction of the ozone layer or through his later scientific work on human-made climate change."
nobelprize.org/prizes/chemist…
Read 9 tweets
Dr. Alex Huffman Profile picture
27 Jan
1/ An interesting editorial by Prof. MacIntyre, infectious disease professor at the @KirbyInstitute at @UNSW. Edited by @mariemcinerney.

She postulates on why the COVID pandemic response has been such a "catastrophic failure of many Western democracies".
croakey.org/the-hijacking-…
2/ For reference, Prof. MacIntyre wrote this scientific editorial with @rajah_mich on 'Scientific evidence supports aerosol transmission of SARS-CoV-2"
aricjournal.biomedcentral.com/articles/10.11…
3/ Much focus on importance of a #multidisciplinary approach. A few interesting quotes:

"The evidence is clear that SARS-COV-2 is airborne, yet guidelines in many countries do not yet reflect this, thus hampering the ability to control the spread and endangering health workers."
Read 6 tweets

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