Thread by @clcazer

The evidence for and against cloth mask use in the general public. 🧵
#Masks4All #epitwitter #AcademicTwitter #AcademicChatter
#ScienceMatters
@mollywood @kairyssdal @Marketplace

The strongest scientific evidence comes from systematic reviews, which look at cumulative results from many studies, followed by randomized controlled trials, then observational studies, laboratory experiments, and then case studies.

Surgical and/or N95 masks are essential PPE for healthcare workers in this fight.
Systematic reviews:
-pubmed.ncbi.nlm.nih.gov/29140516/
-pubmed.ncbi.nlm.nih.gov/29140516/
-onlinelibrary.wiley.com/doi/pdf/10.111…
-cadth.ca/sites/default/…

Observational studies:
-onlinelibrary.wiley.com/doi/full/10.11…
-ncbi.nlm.nih.gov/pubmed/20095070

PPE must be very carefully put on and taken off to avoid contaminating yourself--which defeats the whole purpose of wearing a mask!

Systematic reviews:
-cochranelibrary.com/cdsr/doi/10.10…
-ncbi.nlm.nih.gov/pubmed/26452427

Lit review:
-clinicaltherapeutics.com/article/S0149-…

More on PPE contamination:

Lab experiments:
-aricjournal.biomedcentral.com/articles/10.11…
-…sagepub-com.proxy.library.cornell.edu/doi/pdf/10.117…

Wuhan hospital environments were contaminated by doffing PPE:
-biorxiv.org/content/10.110…

So something (cloth mask) may not be better than nothing. In fact it could be worse!

There is some evidence that wearing a mask if you are sick or caring for someone who is sick will reduce the transmission of viruses in households

Systematic reviews:
-cochranelibrary.com/cdsr/doi/10.10…
-bmj.com/content/350/bm…
-cambridge.org/core/services/…

But masks may not have any additional benefit if you are already washing your hands appropriately

Randomized trial:
-annals.org/aim/fullarticl…

The only controlled trials I've seen on mask use in general populations (college students) found that masks + hand hygiene did not reduce the overall rate of respiratory infections.

Randomized trials:
-ncbi.nlm.nih.gov/pmc/articles/P…
-ncbi.nlm.nih.gov/pubmed/20088690

one observational study on SARS (2003) found that mask use protected against SARS
-wwwnc.cdc.gov/eid/article/10…

What about cloth masks? (if you have a surgical or N95 mask DONATE it to your hospital where it can do the most good)

I can only find one randomized clinical trial. It found cloth masks are NOT effective. (in fact they were worse than the control group!)
-bmjopen.bmj.com/content/5/4/e0…

Lab experiments show that >40% (sometimes up to 90+%) of airborne particles penetrate cloth masks
-ncbi.nlm.nih.gov/pubmed/20584862
-ncbi.nlm.nih.gov/pubmed/27531371
-doi.org/10.1017/dmp.20…
-journals.plos.org/plosone/articl…

Scientists need to be very careful to say that 'finding no evidence' is NOT equal to 'there is no evidence'. We need more studies, better studies, to determine if masks would be helpful for COVID-19 in the general public. This study could be done NOW.

Until then, avoid anecdotes and ecological fallacies (widespread mask use in Asia does not equal control of COVID-19, correlation is not causation, the data are confounded)

If you want to use a cloth mask, look up proper PPE protocol (cdc.gov/hai/pdfs/ppe/p…) AND WASH YOUR HANDS

also many thanks to @rmm257 and friends for the inspiration and help in collating all these articles!

@Rebecca4Georgia made a great webinar reviewing some of these studies.
facebook.com/rebecca4georgi…

of course one can only read so many papers in a few days...
digging more into a sys review cited above (cochranelibrary.com/cdsr/doi/10.10…)

they base masks = best intervention to reduce viral spread, using a lot of papers from SARS 2003 epidemic

most of the papers look at protecting HCW.
2 case-control studies (lower evidence than RCT): wearing masks (type unknown?) in public associated with a lower risk of SARS.
ncbi.nlm.nih.gov/pmc/articles/P…
ncbi.nlm.nih.gov/pmc/articles/P…