
Modeling the effectiveness of respiratory masks in reducing influenza (2018) - Terretta
https://www.ncbi.nlm.nih.gov/pubmed/30229968
======
Leary
The US has 12 million N95 in stockpile, another 5 million N95 that expired.

The US has 30 million surgical masks in stockpile.

The US needs 300 million N95 masks for medical professionals. [1]

[1] [https://www.cnbc.com/2020/02/28/us-mulls-using-sweeping-
powe...](https://www.cnbc.com/2020/02/28/us-mulls-using-sweeping-powers-to-
ramp-up-production-of-coronavirus-protective-gear.html)

Therefore it is rational for public health policy to reserve high quality
masks for medical professionals, regardless of their effectiveness for the
general public.

I wonder how many masks they can manufacture a week in this emergency.

~~~
dawnerd
I've seen a lot of people suggest not buying the masks when they're in stock
at hardware stores so 'hospitals can have some' which I find absolutely
hilarious - Just the image of a hospital sending staff down to a Home Depot
for some N95 paint masks...

~~~
jtbayly
I know a story of an ER doctor sending somebody to the hardware store for a
tool. My brother also had a regular tool used during his visit to the ER. I
don’t think it’s outside the realm of possibility that they simply purchased
it at the hardware store. (It was a dremel with a diamond blade to remove his
aircraft-grade aluminum ring from an injured finger. Let that be a warning to
you about what you put on your finger.)

~~~
ethbro
Out of morbid curiosity, how'd they get it off?

Slip a super-hard, super-thin backer underneath it, then cut? (Aluminum
probably being the best scenario, as far as industrial metals go)

~~~
londons_explore
Just cut directly. A tiny scratch and a tiny burn from the heat of the cutting
disc, but nothing worse than a paper cut.

------
tristanj
More here: Study finds N95 masks reduce risk of coronavirus infection
[https://www.livescience.com/respirators-prevent-
coronavirus-...](https://www.livescience.com/respirators-prevent-coronavirus-
infection-study.html)

 _As Wang 's study revealed, rates of infection differed between doctors and
nurses with [N95] respirators and those without._

 _Specifically, the authors examined data collected from Jan. 2-22 at six
departments within the Zhongnan Hospital. Within the 10-day period, the
hospital treated 28 individuals with confirmed cases of COVID-19 and 58
"suspicious" cases. The medical staff in each department followed different
safety protocols when treating the patients._

 _About 280 medical staff in the hospital 's Respiratory, ICU and Infectious
Diseases departments wore N95 respirators and washed their hands frequently,
while about 215 in the departments of Hepatobiliary Pancreatic Surgery, Trauma
and Microsurgery, and Urology wore no masks and disinfected their hands less
frequently. Although the respirator group encountered confirmed cases more
often than the unmasked group — more than 730% more often — no one in the
respirator group became infected._

 _In comparison, 10 people in the unmasked group contracted the novel disease,
despite treating fewer infected patients._

 _" It would appear that N95 respirators, no surprise, protect against health
care acquisition of the virus," said Dr. William Schaffner, an infectious-
diseases specialist at Vanderbilt University in Tennessee, who was not
involved in the current study. The small study is "reassuring in that sense,"
although there was no reason to think that N95 respirators wouldn't block out
the novel coronavirus effectively, he added._

~~~
tgb
So the mask group was also competely confounded with being infectious disease
specialists? Perhaps there were other precautions besides masks and hand
washing that they were taking due to their training, even if not explicitly.
Still interesting, particularly given the widespread appearance of "don't
bother with masks" articles these days.

~~~
joe_the_user
I don't think you can call multiple elements to a protocol a "confounding
factor".

Study: "wearing a mask and washing your hands has been shown to stop
infection."

Critic: "This study is worthless, it can show which of these procedures was
effective!"

Study: "uh, err..."

Confounding factors would uncontrollable factors that people couldn't
implement themselves. People can clearly wash their hands and wear masks.

~~~
tgb
That's simply not what I said. The confounding factor isn't hand washing
(though that also makes it impossible "model the effectiveness of respiratory
masks" as the title says), it's that it's comparing one department to other
departments, and those departments surely differ by more than just hand
washing and face masks. Infectious disease specialists were trained
differently, do different procedures, etc. They see patients with different
symptoms and at different stages of their disease.

Essentially the way to treat this is not a study of N doctors but a study of
only n departments, which turns it more into an anecdote - albeit a compelling
one.

------
ruxmtl
Anyone have any info on the comparability of COVID-19 to H1N1 in terms of
transmission methods since we have official trace data, studies and reports on
H1N1? Am having this discussion and being pointed out the fact that H1N1's
particulate size is actually smaller than COVID-19 (80-120nm vs 200nm
respectively).

------
KKKKkkkk1
According to Google Scholar, this paper has zero citations. This does not
engender too much trust in its results.

------
blackrock
For something like this, I wonder why the health workers haven’t started using
those positive-pressure helmet hazmat suits. Like those from that Outbreak
movie.

------
dieselerator
I wonder how it feels to be assigned to the control group?

------
gyrgtyn
This seems very simple and cost effective?

------
droithomme
Thanks for this. The US Surgeon General needs to be fired and delicensed from
medical practice after his claim yesterday that no one should buy masks
because masks don't work. He has no business representing himself as a
qualified medical professional.

His statements are such egregious malpractice that they rise to the caliber of
extreme negligence and should expose him given his position to liability and
possibly criminal charges for contributory homicide.

South Korea is looking at charging church officials with "murder through
willful negligence" ([https://www.nytimes.com/2020/03/01/world/coronavirus-
news.ht...](https://www.nytimes.com/2020/03/01/world/coronavirus-news.html)).
The reason? They told church members to remove their masks during services as
it was "disrespectful to God." Telling people not to wear masks is murder
through willful negligence.

~~~
asdff
Masks don't protect you from others, they protect others from you, and if you
are a health professional dealing with infected people from vulnerable
populations, or a surgeon asking for a scalpel over an open body, you are
going to assume that you are infected and capable of transmitting disease out
of an abundance of caution. Masks for the general healthy public is borderline
hysteria and affects the medical supply chain.

~~~
nec4b
Respiratory masks do indeed protect you from others. This is the whole point
of this article.

~~~
asdff
I wasn't saying n95 respirators don't do anything. They are very effective. I
was talking about disposable surgical masks that people are now wearing
everywhere.

~~~
droithomme
You should consider reading the scientific study that this entire thread is
about.

 _> In this article, a risk assessment model previously developed in general
form was used to estimate the effectiveness of different types of protective
equipment in reducing the rate of infection in an influenza outbreak. It was
found that a 50% compliance in donning the device resulted in a significant
(at least 50% prevalence and 20% cumulative incidence) reduction in risk for
fitted and unfitted N95 respirators, high-filtration surgical masks, and both
low-filtration and high-filtration pediatric masks. An 80% compliance rate
essentially eliminated the influenza outbreak._

It's not the only study.

[https://www.sciencedaily.com/releases/2019/09/190903134732.h...](https://www.sciencedaily.com/releases/2019/09/190903134732.htm)

 _> Summary: The study reported 'no significant difference in the
effectiveness' of medical masks vs. N95 respirators for prevention of
influenza or other viral respiratory illness. _

------
bouncycastle
I did my own little experiment with masks which you can also easily repeat the
experiment yourself.

Note that this works on the regular masks you can buy from regular shops such
as convenience stores that the general public mostly wears.

Put on the mask in cold weather or a chill room and then take a deep breath
and breathe out. You will notice a lot of steam is coming off around the sides
of the masks and especially around the nose area where these masks are not
sealed. Worse if you cough of sneeze! This is even more so after the mask has
been worn for some time and gets soggy.

Next, go outside and ask your friend to light a cigarette and exhale smoke in
your face while you take a deep breath through your nose. (Wearing the mask as
you would normally do). You will find a lot of smoke gets around the mask,
mostly around the edges around the nose.

You can make your own conclusions from there. My conclusion was that these
things are mostly toys and the majority of people wearing them either do not
fit them correctly or do not change often or both, and they also may be
putting too much confidence in them.

~~~
saurik
As I imagine you are expecting to test for smoke in that case by seeing if you
can smell it: of course you can smell it, as what you are smelling there is a
gas. An N95 mask filters particles larger than some reasonably large size,
which hopefully includes giant encapsulated viruses filled with genetic
material but is not going to include the odor from smoke which is made up of
individual molecules of stuff like syringol. An N95 mask is not some kind of
"only oxygen and nitrogen and carbon dioxide (and whatever else you absolutely
need from air)" filter: it is just that most scents thankfully aren't harmful,
but happen to be correlated with stuff that is.

FWIW, when I wear an N95 mask I do _not_ get steam from its edges (that is
either a ludicrously poor fit or you are expecting to be able to breath out
too quickly for your mask design), but you also need to remember that
breathing out is "safe" while breathing in is not, and yet the pressure in the
two cases is very different, so something can be very effective even if it has
the issue you are complaining about (and some masks are even designed
specifically like that, with pressure vents to make breathing easier so you
can exhale quickly without a problem and then pull air in more slowly where
the feedback is more clear).

~~~
Reelin
> giant encapsulated viruses filled with genetic material

Somewhat tangential, but viruses are actually _really_ small. Some approximate
sizes for comparison:

* Pollen: 20 - 35 um

* E. coli: 2 um

* HEPA filter: 99.97% capture at 0.3 um

* N95: 95%+ at 0.1 - 0.3 um [1]

* Sterilizing filter pore size: 0.22 um

* Virus: 0.004 - 0.1 um

Even the sterilizing filter in the lab doesn't remove viruses. I'm not
actually sure what mechanics are going on in this case that allow an N95 to
protect you.

[1]
[https://www.ncbi.nlm.nih.gov/pubmed/9487666](https://www.ncbi.nlm.nih.gov/pubmed/9487666)

~~~
ve7ftz
Masks actually have kind of a funny response curve (see 5th page of linked
PDF).

The masks are basically made out of layers of tiny (as small as 1um) fibres
that force the air to weave through them to get to you. Larger particles tend
to hit fibres on their way through, while smaller ones tend to get pushed out
of the way of bigger things like air molecules rushing through and get bumped
into the fibres and captured. The things that get though are the ones in the
sweet spot of being small enough to make their way around the fibres in the
air, but large enough to not simply be knocked out of the path by the air
molecules themselves.

The lowest efficiency is around 0.04-0.1um on the models tested (so perfect
range for most viruses) but even then they were still only dropping to like
94% effectiveness. I expect “94% effective” is still enough to see a
significant different but that’s just my gut feeling.

All kind of moot, though, as coronaviruses (per 4th page of linked PDF) are
actually closer to 0.125um, which is veering back to 100% effectiveness. And
if we expect that a lot of transmission is happening in droplets, those are
_much_ larger and easily caught by the filter.

[https://multimedia.3m.com/mws/media/409903O/respiratory-
prot...](https://multimedia.3m.com/mws/media/409903O/respiratory-protection-
against-biohazards.pdf)

