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What does a mask do? Blocks respiratory droplets coming from your mouth and throat.
Two simple demos:
First, I sneezed, sang, talked & coughed toward an agar culture plate with or without a mask. Bacteria colonies show where droplets landed. A mask blocks virtually all of them.
Two simple demos:
First, I sneezed, sang, talked & coughed toward an agar culture plate with or without a mask. Bacteria colonies show where droplets landed. A mask blocks virtually all of them.
What about keeping your distance?
Second demo: I set open bacteria culture plates 2, 4 and 6 feet away and coughed (hard) for ~15s. I repeated this without a mask.
As seen by number of bacteria colonies, droplets mostly landed <6 ft, but a mask blocked nearly all of them.
Second demo: I set open bacteria culture plates 2, 4 and 6 feet away and coughed (hard) for ~15s. I repeated this without a mask.
As seen by number of bacteria colonies, droplets mostly landed <6 ft, but a mask blocked nearly all of them.
I'm aware that this simple (n=1) demo isn't how you culture viruses or model spread of SARS-CoV-2.
But colonies of normal bacteria from my mouth/throat show the spread of large respiratory droplets, like the kind we think mostly spread #COVID19, and how a mask can block them!
But colonies of normal bacteria from my mouth/throat show the spread of large respiratory droplets, like the kind we think mostly spread #COVID19, and how a mask can block them!
My mask vs. no mask demonstrations got perfectly summarized in this brief 34 second video. Masks keep your respiratory secretions to yourself! @providence_phc https://twitter.com/providence_phc/status/1276619220957233154?s=20
Something extra cool, local reporter Kevin Kim came to our teaching lab and tried this same demonstration himself (his reaction in this clip was absolutely genuine). Story airs tonight @KHQLocalNews
The take home: masks matter! https://twitter.com/NewsWithKevin/status/1276605461819580416?s=20
The take home: masks matter! https://twitter.com/NewsWithKevin/status/1276605461819580416?s=20
Masks as a political/social litmus test or used to shame those who won't (or disabled folks who truly can't!) wear them is a travesty.
We wash hands after using the bathroom & wipe noses on tissues. Masks/face shields need to be just another normalized act of hygiene. #MasksWork
We wash hands after using the bathroom & wipe noses on tissues. Masks/face shields need to be just another normalized act of hygiene. #MasksWork
Well I just got back from reading some slides in the lab and this has completely overwhelmed my ability to keep up with comments and questions. Wow.
I'll circle back later tonight to answer questions. Thanks everyone!
I'll circle back later tonight to answer questions. Thanks everyone!
I saw a number of people ask this: how did I sneeze on command?
I actually got a packet of pepper from the cafeteria to try to make myself sneeze - didn't work, just got watery eyes. So I just did a fake stage-sneeze at the plate. https://twitter.com/ShelbyHintze/status/1276632641136025600?s=20
I actually got a packet of pepper from the cafeteria to try to make myself sneeze - didn't work, just got watery eyes. So I just did a fake stage-sneeze at the plate. https://twitter.com/ShelbyHintze/status/1276632641136025600?s=20
When reporter @NewsWithKevin did this experiment, he sang twice. Once he sang Smashmouth's "All Star" and on a different plate rapped Tupac's "Things Will Never Change." The Tupac plate had more bacteria.
Literally spitting verses ... https://twitter.com/EBabady/status/1276649843646181377?s=20
Literally spitting verses ... https://twitter.com/EBabady/status/1276649843646181377?s=20
The clip from tonight's @KHQLocalNews with reporter Kevin Kim repeating this experiment (and reacting to the results) is here. I think this turned out really well! Awesome job Kevin! @NewsWithKevin @providence_phc https://www.khq.com/news/khq-investigates-how-effective-is-a-mask/video_e308a1e8-b74f-11ea-ac6d-878bd6f54032.html
A lot of people asked this: "could you do this with ___ type of mask?" (homemade, single layer, cotton, N95 etc.)
So it's not a bad idea but I would honestly expect the outcome of THIS demonstration to be essentially the same and here's why...
https://twitter.com/argyleumbrella/status/1276702335599697921?s=20
So it's not a bad idea but I would honestly expect the outcome of THIS demonstration to be essentially the same and here's why...
https://twitter.com/argyleumbrella/status/1276702335599697921?s=20
I try to be really clear what this does & does not show.
DOES SHOW: the act of talking (or coughing, sneezing, singing) causes particles of liquid to come out of your mouth.
DOES SHOW: those droplets can carry microbes like bacteria
DOES SHOW: a mask blocks most of those
DOES SHOW: the act of talking (or coughing, sneezing, singing) causes particles of liquid to come out of your mouth.
DOES SHOW: those droplets can carry microbes like bacteria
DOES SHOW: a mask blocks most of those
DOES NOT SHOW: what is the number, size, and distribution of respiratory droplets produced by coughing/talking etc.
DOES NOT SHOW: could these droplets carry viruses (like SARS-CoV-2), does a mask block THOSE
(Based on what we know you can intuit/infer this, but it's not shown)
DOES NOT SHOW: could these droplets carry viruses (like SARS-CoV-2), does a mask block THOSE
(Based on what we know you can intuit/infer this, but it's not shown)
Something I repeated enough while talking that reporter Kevin finally asked, "Why do you keep calling it a 'demonstration' and not an 'experiment'?"
To me this is purely a demonstration bc 1) it was just one single data point and 2) I essentially knew the outcome going in
To me this is purely a demonstration bc 1) it was just one single data point and 2) I essentially knew the outcome going in
I *knew* that coughing on a agar plate would get my mouth bacteria on there and I knew that a mask would decrease that amount (maybe even completely).
I used a surgical mask from a hospital. Would a homemade mask do the same and keep mouth bacteria from the plates? Certainly.
I used a surgical mask from a hospital. Would a homemade mask do the same and keep mouth bacteria from the plates? Certainly.
If I was trying to compare the ability of
- disposable paper mask
- hospital surgical mask
- homemade fabric mask
- N95 mask
- PAPR
to reduce virus transmission, I wouldn't do what I did here, which is see how well a mask blocks minute bits of spit using # of bacteria as a proxy
- disposable paper mask
- hospital surgical mask
- homemade fabric mask
- N95 mask
- PAPR
to reduce virus transmission, I wouldn't do what I did here, which is see how well a mask blocks minute bits of spit using # of bacteria as a proxy
So COULD you test different masks with this same set up? Yes. Would it be different? Eh. Probably not.
A mask preventing your spit & breath from flying out of your mouth, even if doesn't catch it all, will stop some spread of bacteria (see here) AND LIKELY VIRUS (not seen here)
A mask preventing your spit & breath from flying out of your mouth, even if doesn't catch it all, will stop some spread of bacteria (see here) AND LIKELY VIRUS (not seen here)
OK here's what was probably the most common question I saw: what did I sing at (to??) my culture plates.
It was "Dear Theodosia" from Hamilton, top of my lungs.
If I could have anyone's singing talent it would be Leslie Odom Jr.'s. (Spoiler: I don't.) https://twitter.com/feline_cannon/status/1276653662073319424?s=20
It was "Dear Theodosia" from Hamilton, top of my lungs.
If I could have anyone's singing talent it would be Leslie Odom Jr.'s. (Spoiler: I don't.) https://twitter.com/feline_cannon/status/1276653662073319424?s=20
100% true: bacteria are incredibly different from viruses!
But since we expect respiratory droplets to be what primarily spreads #COVID19, I exploit the presence of (easily to grow and visualize) bacteria in respiratory droplets, to show where they go. https://twitter.com/curlfw/status/1276710062807871488?s=20
But since we expect respiratory droplets to be what primarily spreads #COVID19, I exploit the presence of (easily to grow and visualize) bacteria in respiratory droplets, to show where they go. https://twitter.com/curlfw/status/1276710062807871488?s=20
"Microbiology in six words or less..." https://twitter.com/lindsaygoldwert/status/1276730396575707136?s=20
Itâs Friday night and a bunch of nice people are recommending I pull out my nose hair. Things are ver normal and good ... 
You certainly COULD do this. But I was not be trying to quantitate # of droplets/bacteria colonies spread by diff. behaviors or exactly how far. More sophisticated techniques than this show droplet spread by just breathing... https://twitter.com/JeremyMichelson/status/1276656755959754752?s=20
It's a fun idea testing distance of droplets spread by talking, breathing, singing etc. (what about diff. types of songs? Trained or professional singer?)
Would it "prove" that singing can really spread droplets? I think we already know that's the case: https://www.cnn.com/2020/05/13/us/coronavirus-washington-choir-outbreak-trnd/index.html
Would it "prove" that singing can really spread droplets? I think we already know that's the case: https://www.cnn.com/2020/05/13/us/coronavirus-washington-choir-outbreak-trnd/index.html
This could be a fun thing you could do. However, I don't think it would model protection to the mask weaver very well (at least with this simple experiment design....) https://twitter.com/InternFrench/status/1276709773673668611?s=20
Inhaling is an active, high-velocity process, just like exhaling, coughing, and sneezing are.
A mask sitting on top of a plate will certainly block any droplets that come flying at it. But a person breathing in droplets coughed out by another person? Different story.
A mask sitting on top of a plate will certainly block any droplets that come flying at it. But a person breathing in droplets coughed out by another person? Different story.
Unless it's a fit-tested respirator, your surgical or cloth mask won't have an air tight seal. When you inhale, if air finds the path of least resistance, a lot will go in on the sides... (video from LaVision showing air currents w/ and w/o a man's N95) https://twitter.com/PDChina/status/1247167174453506048?s=20
Someone (sorry I can't find who) asked, could I try to catch droplets coming out the SIDE of a surgical mask.
I don't think a bacteria plate-based readout would answer the real question which is "where do THOSE exhalations/droplets go?" I don't know but it won't be out in front.
I don't think a bacteria plate-based readout would answer the real question which is "where do THOSE exhalations/droplets go?" I don't know but it won't be out in front.
Well this has been like nothing I could've expected.
There are replies to a few often-repeated questions in the above thread but a lot of these keep getting re-asked. If you've asked something new, chances are good I'll miss it because, yikes, this got pretty big.
There are replies to a few often-repeated questions in the above thread but a lot of these keep getting re-asked. If you've asked something new, chances are good I'll miss it because, yikes, this got pretty big.
It's been really great interacting with people, seeing other language translations and so many good questions and comments.
Overwhelmingly I've only seen positive responses so thanks for that. Going to get some rest. Thanks! #Masks4All #FaceShieldsForAll
Overwhelmingly I've only seen positive responses so thanks for that. Going to get some rest. Thanks! #Masks4All #FaceShieldsForAll
It's now three days later and things are still going pretty strong.
Going to add to this thread a few additional ideas, reminders and answers. Away we go!
Going to add to this thread a few additional ideas, reminders and answers. Away we go!
I think most of the questions/criticisms I've seen are things that I believe I already addressed enough, but I can circle back on some of them:
"Bacteria =/= viruses!!"
Yes, but large droplets that can carry/deposit both get blocked by masks. https://twitter.com/richdavisphd/status/1276629366789697536
"Bacteria =/= viruses!!"
Yes, but large droplets that can carry/deposit both get blocked by masks. https://twitter.com/richdavisphd/status/1276629366789697536
Not only *can* large droplets carry viruses, but itâs thought that this is the primary way #COVID19 is spread.
Therefore, blocking those droplets? A primary way of preventing that spread.
This @STATnews article (from March!) covers lot of that ground
https://www.statnews.com/2020/03/16/coronavirus-can-become-aerosol-doesnt-mean-doomed/#:~:text=The%20reason%20the%20measles%20is,exist%20as%20a%20true%20aerosol.
Therefore, blocking those droplets? A primary way of preventing that spread.
This @STATnews article (from March!) covers lot of that ground
https://www.statnews.com/2020/03/16/coronavirus-can-become-aerosol-doesnt-mean-doomed/#:~:text=The%20reason%20the%20measles%20is,exist%20as%20a%20true%20aerosol.
So, even if SARS-CoV-2-containing particles exist as an aerosol in measurable but limited capacity, likely not âdriving the pandemicâ (if it were, things would be worse than they are!).
Also the question of *detectable* virus not necessarily being *infectious dose* of virusâŠ
Also the question of *detectable* virus not necessarily being *infectious dose* of virusâŠ
Last thing here, I think this paragraph summarizes a lot of this:
Coronavirus expert Dr. Stan Perlman (actually my first mentor in grad school!): "You have to distinguish between whatâs possible and whatâs actually happening." https://www.statnews.com/2020/03/16/coronavirus-can-become-aerosol-doesnt-mean-doomed/#:~:text=The%20reason%20the%20measles%20is,exist%20as%20a%20true%20aerosol.
Coronavirus expert Dr. Stan Perlman (actually my first mentor in grad school!): "You have to distinguish between whatâs possible and whatâs actually happening." https://www.statnews.com/2020/03/16/coronavirus-can-become-aerosol-doesnt-mean-doomed/#:~:text=The%20reason%20the%20measles%20is,exist%20as%20a%20true%20aerosol.
Lots of people asked, "Please test a homemade mask vs. [other mask like an N95]? What if it was outdoors?"
IMO this simple experiment isn't robust enough to answer those questions one way or another.
Would absence of colonies "prove" that all mask types are equally good? No.
IMO this simple experiment isn't robust enough to answer those questions one way or another.
Would absence of colonies "prove" that all mask types are equally good? No.
OK, something I'm ashamed I didn't explain: âWhat exactly are these "plates"?â
They're bacteria culture plates: Petri dishes with agar (gelatinous, solid even when warmer than room temp), with additives, nutrients to promote bacterial growth. https://twitter.com/richdavisphd/status/1265443436917735425?s=20
They're bacteria culture plates: Petri dishes with agar (gelatinous, solid even when warmer than room temp), with additives, nutrients to promote bacterial growth. https://twitter.com/richdavisphd/status/1265443436917735425?s=20
Red plates some people said looked like "ketchup with pepper dumped on top" are Sheep Blood Agar (literal sheep blood mixed in to the agar).
Brown plates are "Chocolate" Agar, but surprise, it's not chocolate, it's ALSO blood (just heated till the RBCs pop). Bacteria love these.
Brown plates are "Chocolate" Agar, but surprise, it's not chocolate, it's ALSO blood (just heated till the RBCs pop). Bacteria love these.
"Surprise! It's not chocolate, it's *ALSO* blood!" is a fun line to slip into casual conversations if you want to shock and horrify your non-microbiologist friends...
Oh, "why are they different sizes?"
The smaller plates are the standard plates we use for culturing/isolating bacteria colonies. The larger plates are used for disk diffusion antibiotic testing.
This large one was near its expiration date. This seemed like a good use for itâŠ
The smaller plates are the standard plates we use for culturing/isolating bacteria colonies. The larger plates are used for disk diffusion antibiotic testing.
This large one was near its expiration date. This seemed like a good use for itâŠ
Obviously I knew I wasn't the first person to have done this, but this blew me away.
Shared by @TanguyFilloux, it's an article from from December 13, 1918 edition of the California Aggie newspaper, summarizing a "Harvard University experiment" https://twitter.com/TanguyFilloux/status/1276690488578330625
Shared by @TanguyFilloux, it's an article from from December 13, 1918 edition of the California Aggie newspaper, summarizing a "Harvard University experiment" https://twitter.com/TanguyFilloux/status/1276690488578330625
Found this article in digital format here: https://cdnc.ucr.edu/?a=d&d=UCD19181213.2.19.1&e=-------en--20--1--txt-txIN--------1
Man puts culture broth at diff lengths on a lecture hall table. He drinks (!!) a "germ laden liquid," then talks, talks loudly, sneezed and coughed to measure distance.
"Moral: wear your mask."
Dec 13, 1918
Man puts culture broth at diff lengths on a lecture hall table. He drinks (!!) a "germ laden liquid," then talks, talks loudly, sneezed and coughed to measure distance.
"Moral: wear your mask."
Dec 13, 1918
Interestingly, this poem appears in the same Dec 12 (not 13th) 1918 edition of the California Aggie as the "Harvard experiment"
So it sounds like people living through the 1918 influenza also had people saying "it's just the flu."
So it sounds like people living through the 1918 influenza also had people saying "it's just the flu."
Haven't had time to go looking for where/if the actual study was published, but it seems like press releases not citing/linking the original studies was a problem even a hundred years ago! https://twitter.com/JulieMarieWolf/status/1277770254480027654?s=20
Alright just a few more things (and then this thread may be too long and unwieldy to be useful)
A lot of people have asked about face shields and what effect they might have. Answer: a positive one. https://twitter.com/danielwartist/status/1277637018378436614
A lot of people have asked about face shields and what effect they might have. Answer: a positive one. https://twitter.com/danielwartist/status/1277637018378436614
Infectious disease experts from the U of Iowa @eliowa, Michael Emond & @dan_diekema have talked a lot about the value of face shields:
They keep your droplets in, AND they also keep others' from hitting your eyes/face. Easy to make, clean & reuse. Face shields are a great tool.
They keep your droplets in, AND they also keep others' from hitting your eyes/face. Easy to make, clean & reuse. Face shields are a great tool.
How a mask (surgical/cloth face mask vs. an N95) protects *YOU* from a virus has been brought up.
Here's a commentary from @dan_diekema abt why a mask + faceshield (not a respirator) is adequate protection under most conditions, even in a hospital setting https://medcom.uiowa.edu/theloop/announcements/droplet-versus-airborne-precautions-why-we-use-certain-ppe-for-covid-19-patients
Here's a commentary from @dan_diekema abt why a mask + faceshield (not a respirator) is adequate protection under most conditions, even in a hospital setting https://medcom.uiowa.edu/theloop/announcements/droplet-versus-airborne-precautions-why-we-use-certain-ppe-for-covid-19-patients
OK last thing (maybe??)
I said up thread that the overwhelming response to this has been positive.
What I meant was that it's been very positive *toward me* since, actually, there's been a lot retweets/engagments along the lines of "See?? Wear a mask you [expletive] idiots!!!"
I said up thread that the overwhelming response to this has been positive.
What I meant was that it's been very positive *toward me* since, actually, there's been a lot retweets/engagments along the lines of "See?? Wear a mask you [expletive] idiots!!!"
I learned a lot, had to re-examined my own messaging re: masks thanks to @JuliaLMarcus' article "The Dudes Who Wonât Wear Masks"
She connects messages on COVID-19/mask use to AIDS/condom use. An empathy, harm-reduction approach vs a shame & fear-based one https://www.theatlantic.com/ideas/archive/2020/06/dudes-who-wont-wear-masks/613375/
She connects messages on COVID-19/mask use to AIDS/condom use. An empathy, harm-reduction approach vs a shame & fear-based one https://www.theatlantic.com/ideas/archive/2020/06/dudes-who-wont-wear-masks/613375/
Check out this mini-thread of empathetic messaging examples. Acknowledge why it's hard, why it's uncomfortable. It's true and it helps establish trust: https://twitter.com/JuliaLMarcus/status/1277596833548832768?s=20
Adding a few resources on masks that covered a number of points and topics I couldn't (or were outside my expertise).
First this excellent article from @UCSF by Nina Bai quoting experts including @PCH_SF. It covers timelines, evidence & mask types. https://twitter.com/UCSF/status/1278008753498001408?s=20
First this excellent article from @UCSF by Nina Bai quoting experts including @PCH_SF. It covers timelines, evidence & mask types. https://twitter.com/UCSF/status/1278008753498001408?s=20
Second, this "Users Guide to Masks" from @NPRGoatsandSoda. Very clear descriptions of different mask types. @mgodoyh cites experts and studies on basics like "does it protect me or you?" to discussions about what materials to weaves to consider https://twitter.com/NPRGoatsandSoda/status/1278451823519707138
Update: Apparently this alteration of my picture is going around, sometimes with my name still attached.
It's not only fraudulent, but it's wrong: These plates promote the growth/replication of bacteria. A mask does not do this! The inside of your mask =/= these culture plates!
It's not only fraudulent, but it's wrong: These plates promote the growth/replication of bacteria. A mask does not do this! The inside of your mask =/= these culture plates!
A related piece of misinformation I've seen is, "So you're just breathing those bacteria and viruses back in??!!"
You don't *eliminate* viruses or bacteria by breathing them out. If an infection has been established inside of you, it's your immune system that eliminates it.
You don't *eliminate* viruses or bacteria by breathing them out. If an infection has been established inside of you, it's your immune system that eliminates it.
The TYPES of bacteria seen on these culture plates are part of my normal flora (the predominant ones that can grow aerobically anyway). But this is not the AMOUNT of bacteria in my mouth & throat.
If it were, humans' respiratory tracts would be wall-to-wall bacteria sludge.
If it were, humans' respiratory tracts would be wall-to-wall bacteria sludge.
After you've been wearing it, your mask WILL contain moisture and bacteria/viruses you may have exhaled or coughed into it.
That's why you remove it carefully, don't touch the inside, wash your hands afterward and launder it (if fabric) or replace it (following instructions)âŠ
That's why you remove it carefully, don't touch the inside, wash your hands afterward and launder it (if fabric) or replace it (following instructions)âŠ
...but *you* are not put at greater risk of auto-infection by breathing out something you already had.
Your mask doesn't allow your own normal bacteria to replicate to some possibly harmful level. A virus you breathed out was already inside your resp tract.
Keep it to yourself.
Your mask doesn't allow your own normal bacteria to replicate to some possibly harmful level. A virus you breathed out was already inside your resp tract.
Keep it to yourself.
