Thread by @alexdoan96

I've seen this floating around a lot on Twitter and it's frustrating to see science misappropriated like this. It's additionally damaging as many well-meaning folks might see it, think it's credible, and then choose not to wear masks. Well, let's look at the science (1/?).

Before I start, I'm not a doctor and this isn't medical advice. If you have a medical emergency, PLEASE GO SEE A DOCTOR. If any doctors or scientists would like to chime in, I'd love to hear your thoughts. I might be wrong and I'm always trying to learn (2/?)

Starting with the first study: (PMID 18500410).
1) The *lowest* recorded pulse oximeter reading was ~96% SpO2, which is in the normal range (95%+) (3/?)

2) The authors write, "Surgical masks may impose some
measurable airway resistance, but it seems doubtful if this
significantly increases the process of breathing." (4/?)

3) The authors conclude, "This change in SpO2 may be either due to the facial mask or the operational stress, since similar changes were observed in the group performing surgery without a mask." That's right, even a *no-mask* control group had SpO2 drop. (5/?)

Second study: (PMID 32237672).
The quoted text here is a misrepresentation of the authors' actual conclusions. Take a look at the paper itself if you're curious here: nejm.org/doi/10.1056/NE…
(6/?)

The authors write, "More compelling is the possibility that wearing a mask may reduce the likelihood of transmission from asymptomatic and minimally symptomatic health care workers with Covid-19 to other providers and patients." (7/?)

They go on to say, "Masking all providers might limit transmission from [mild/ambiguous cases] by stopping asymptomatic and minimally symptomatic health care workers from spreading virus-laden oral and nasal droplets." (8/?)

I'm going to refer to this study a lot because a LOT of these quotations are misrepresented. A huge issue with this graphic is that it's citing literature that indicate that masks don't protect the wearer. True, but they protect OTHERS. (9/?)

In a pandemic scenario, reducing transmission - especially from asymptomatic/presymptomatic individuals - is critical. Therefore, protecting others is extremely important as well. If a sick individual cannot spread a disease, the disease dies out. (10/?)

Next: The Annals of Internal Med Paper.

This paper was retracted. acpjournals.org/doi/10.7326/L2…

The authors themselves wrote "our findings are uninterpretable."

So...that's that. (11/?)

Next: PMID 32232837
N95's cause headaches. Yes...they're very tight because they need to protect the wearer. Ask any frontline healthcare worker if the protection is worth a headache. (12/?)

Beyond that, the authors speculate that the etiology of headache is most likely due to pressure/strain from the mask - an external compression headache, not one caused by limited gas exchange (although they do mention the possibility) (13/?)

Next: PMID 22188875
The quotation here is completely taken out of context and goes against what the authors actually believe. Here are other quotations from the paper. (14/?)

"Eight of nine retrospective observational studies found that mask and/or respirator use was independently associated with a reduced risk of severe acute respiratory syndrome." (15/?)

They conclude, "Mask use is best undertaken as part of a package of personal protection, especially including hand hygiene in both home and healthcare settings. Early initiation and correct and consistent wearing of masks/respirators may improve their effectiveness." (16/?)

And besides - remember what I said earlier - most studies evaluated whether or not masks protected the WEARERS. Even if they do not, they protect OTHERS. And if I protect you and you protect me, we're all protected. (17/?)

Next: I accidentally skipped over PMID 31289698. Whoops, here goes:
I don't really understand why this is a reason not to wear masks. It's just a reason why you need to replace them. (18/?)

Next: PMID 19216002
First: again, this study only considers the *wearer* of the mask. Therefore, in the context of epidemiology/population-level health, it's not a complete picture of what masks can do - if everyone wears a mask, we are all more protected. (19/?)

On the methodology: this study followed 32 healthcare workers, split into 2 arms (mask/no mask), over 77 days and evaluated frequency of colds. Each group had one cold. Over 77 days. (20/?)

I'm sure there's more that went into this study, but I don't know how the authors can attribute a single cold in both arms to wearing masks or not wearing masks while at work. I get most of my colds in my sleep... (20/?)

Furthermore, this doesn't show masks are dangerous by any means - if anything, it just shows they're not a panacea for cold prevention. Which I haven't seen anyone claiming recently. (21/?)

Next: PMID 20092668.
Take a look at this article and then look at the one sentence that was cherrypicked for this very misleading and dangerous graphic. Because...hoo boy, this article *absolutely* supports mask wearing. Here's some more context. (22/?)

The authors note, "There is some evidence to support the wearing of masks or respirators during illness to protect others, and public health emphasis on mask wearing during illness may help to reduce influenza virus transmission," AKA wearing a mask protects others (23/?)

I think the best part of this study is the 4 other studies they cite - let's take a look at a table summarizing findings: (24/?)

If correct interventions are made, masks and good hand hygiene do seem to reduce the chance of infection in a community setting. I'd love to hear someone chime in on this one - it's the one I feel most shaky about. (25/?)

Next: PMID 25903751
This doesn't say cloth masks are worse than nothing, it's arguing cloth masks are worse than *medical* masks...which is pretty expected. But again - our favorite flaw in application of these studies strikes again...(26/?)

This study, like many others before, is only examining protection for the WEARER. We know that SARS-CoV-2, the virus that causes COVID-19, can travel on droplets. And masks help catch or at least slow down said droplets. (27/?)

Next: the Medical News Today article.
Thanks for describing the etiology of respiratory acidosis. The article, in the "causes" section, mentions *nothing* about masks causing respiratory acidosis. This is a non-starter. (28/?)

Next: the University of Edinburgh pre-print.
This paper examines the protective capabilities of surgical and hand-made masks vs. respirators and face shields. So keep that in mind while evaluating the paper - it's not really a surprise that cloth masks =/= N95's. (29/?)

With that being said, the paper still finds that even handmade masks reduce how far your breath escapes in some directions: (30/?)

They especially help with front throughflow during coughing: (31/?)

What the authors are pointing out, however, is that airflow gets redirected up and to the sides due to masks - which makes sense. However, reducing frontal flow matters - if you're talking to someone, they're probably standing in front of you. (32/?)

Which finally brings me to the last (JAMA) article:
This is the last article so of course I get to use my favorite point - this article is again concerned with protecting the *wearer*, not the *community*. And at this point, you're probably tired of me explaning this point (33/?)

Plus of course - why take my word for it? I'm just an M0.
Well, here's commentary from The Lancet:
thelancet.com/journals/lance…
(34/?)

Of note, "we suggest a stronger public health rationale [for wearing masks] is source control to protect others from respiratory droplets." The authors go on to write... (35/?)

"Previous research on the use of masks in non-health-care settings had predominantly focused on the protection of the wearers and was related to influenza or influenza-like illness.14 These studies were not designed to evaluate mass masking in whole communities..." (36/?)

"...But absence of evidence of effectiveness from clinical trials on mass masking should not be equated with evidence of ineffectiveness. There are mechanistic reasons for covering the mouth to reduce respiratory droplet transmission." (37/?)

Science is constantly evolving. We update our recommendations based on what we've learned. I am sorry to those who are confused about the switch in mask guidance, but the medical and scientific community is now quite united in asking you to please wear a mask. (38/?)

Finally, sometimes the best evidence just comes from what's unfolding around us. And there, we can see that countries with good mask adherence are doing better. Take for example Hong Kong. (39/?)

Early on in the COVID-19 pandemic, 98.8% of respondents to a survey said they wore face masks. While many factors go into infection control, 16 days after their first COVID-19 case, only 12 local cases were confirmed (40/?)
atsjournals.org/doi/pdf/10.116…

And while it's true that HK has seen 2 more waves of COVID-19, despite their very high population density they still have a per-capita caseload 40 times less than the US. Their death rate? 210 times lower. Two hundred and ten. (41/?)

Anyways...thank you for reading this if you made it this far. I know this is a lot, but I also think putting science into context - especially when it can save lives - is critically important. As said before - please correct me on my own misunderstandings. (42/?)

I am trying to set the record straight on the deliberate, dangerous cherrypicking that informed this image I've seen widely disseminated, but at the same time I don't want to myself spread incorrect information. (43/?)

Stay safe, stay well, be kind to each other - and please...WEAR A MASK! (44/44)

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