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Well, it looks like 
https://abs.twimg.com/emoji/v2/... draggable="false" alt="😷" title="Gesicht mit Mundschutz" aria-label="Emoji: Gesicht mit Mundschutz">are in the news again. With Dr. Atlas posting doubt that masks are effective (and @Twitter subsequently squashing the tweet), it’s probably time for a quick refresher (just in case anyone is still wondering). Let& #39;s answer the misinformation with data 1/11
First off. Here’s a quick reminder that, yes, COVID can spread before symptoms develop. This contact tracing study from Taiwan found a small, but statistically significant risk of acquiring COVID-19 even when exposed to pre-symptomatic patients. https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2765641">https://jamanetwork.com/journals/... 2/11
So, do masks work? A lot of different types of studies evaluate this question. One of the more interesting ways to look at this is to look at local infection rates before & after mask mandates. It’s sort of an observational study. 3/
Here in the great state of #Ohio, we saw a large (34.9%) reduction in COVID-19 incidence in the month after
@GovMikeDeWine instituted mask mandates https://www.msn.com/en-us/news/us/ohios-coronavirus-cases-drop-after-statewide-mask-order-dramatically-so-in-some-counties/ar-BB18sBRa">https://www.msn.com/en-us/new... 4/
@GovMikeDeWine instituted mask mandates https://www.msn.com/en-us/news/us/ohios-coronavirus-cases-drop-after-statewide-mask-order-dramatically-so-in-some-counties/ar-BB18sBRa">https://www.msn.com/en-us/new... 4/
Next, a retrospective cohort study from Beijing. 335 people in 124 families with at least 1 lab conf. case. Mask use by the case and family contacts before symptom onset was 79% effective in reducing transmission (OR=0.21, 95% CI 0.06 to 0.79). https://gh.bmj.com/content/5/5/e002794">https://gh.bmj.com/content/5...
Next, the holy grail; the meta-analysis. This one in
@TheLancet
looked at over 170 studies evaluating MERS, SARS & COVID-19. Masks (both in health care & non-HC settings) led to reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7)
@TheLancet
looked at over 170 studies evaluating MERS, SARS & COVID-19. Masks (both in health care & non-HC settings) led to reduction in risk of infection (n=2647; aOR 0·15, 95% CI 0·07 to 0·34, RD −14·3%, −15·9 to −10·7)
A picture is worth a thousand words. From
@TheLancet study
https://thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext">https://thelancet.com/journals/...
@TheLancet study
https://thelancet.com/journals/lancet/article/PIIS0140-6736(20)31142-9/fulltext">https://thelancet.com/journals/...
Honestly, though, this may be my favorite.
@DukeHealth experience. 70% of HCWs acquired COVID from co-workers not patients. They flattened this curve with a universal mask mandate. The elegance of this small study was the use of community-acquired incidence in HCWs as a control
@DukeHealth experience. 70% of HCWs acquired COVID from co-workers not patients. They flattened this curve with a universal mask mandate. The elegance of this small study was the use of community-acquired incidence in HCWs as a control
Masks basically drove the rate of new cases acquired at work to near zero.
https://cambridge.org/core/services/aop-cambridge-core/content/view/9301E77612122039190A29CB7223F9C4/S0899823X2000313Xa.pdf/universal_masking_is_an_effective_strategy_to_flatten_the_sarscov2_healthcare_worker_epidemiologic_curve.pdf">https://cambridge.org/core/serv...
https://cambridge.org/core/services/aop-cambridge-core/content/view/9301E77612122039190A29CB7223F9C4/S0899823X2000313Xa.pdf/universal_masking_is_an_effective_strategy_to_flatten_the_sarscov2_healthcare_worker_epidemiologic_curve.pdf">https://cambridge.org/core/serv...
Finally, these articles evaluate if a mask protects the wearer, but remember, my mask protects you and yours protects me. This article argues that absence of evidence in this case means we SHOULD wear a mask until we have evidence of harm. the “precautionary principle.” 10/
Basically, even limited protection could prevent some COVID-19 transmission and save lives and because this is such a serious threat, wearing masks in public should be advised. https://www.bmj.com/content/369/bmj.m1435">https://www.bmj.com/content/3... 11/15
Also, as a post-script, I left out the purely anecdotal case reports, but these two are pretty powerful examples. The first being the absence of COVID transmission in nearly 140 patrons of 2 symptomatic hair stylists with confirmed COVID-19 12/15 https://www.cdc.gov/mmwr/volumes/69/wr/mm6928e2.htm">https://www.cdc.gov/mmwr/volu...
The second powerful anecdote is the man on a 15 hr flight who developed symptoms of COVID-19 en route and later tested positive. He was wearing a mask, but packed into coach. ZERO of the contacts tested positive. 13/15 https://www.cmaj.ca/content/192/15/E410">https://www.cmaj.ca/content/1...
Compare to a recent CDC study from September of a case in March on an airplane with a 62% attack rate. Mask usage is unknown for this study, but this occurred before mask usage was recommended in vogue, so presumably can work as a control 14/15 https://wwwnc.cdc.gov/eid/article/26/11/20-3299_article">https://wwwnc.cdc.gov/eid/artic...
So, in summary.
1) Presymptomatic transmission happens
2) Yes,https://abs.twimg.com/emoji/v2/... draggable="false" alt="😷" title="Gesicht mit Mundschutz" aria-label="Emoji: Gesicht mit Mundschutz">= https://abs.twimg.com/emoji/v2/... draggable="false" alt="⬇️" title="Pfeil nach unten" aria-label="Emoji: Pfeil nach unten">risk, esp if prolonged close contact
3) Precautionary principle states we should #maskup until we know we shouldn& #39;t.
4) Yes, these studies are >3 months old. Why are we still talking about this??? 15/15
1) Presymptomatic transmission happens
2) Yes,
3) Precautionary principle states we should #maskup until we know we shouldn& #39;t.
4) Yes, these studies are >3 months old. Why are we still talking about this??? 15/15
@threadreaderapp @UnrollHelper please unroll
