Thread by @MackayIM

Yes. Cloth masks (less so than surgical masks & less again than N95 respirators) *can* reduce risk of inhaling potentially (an as yet unproven, but possible route of SARS-CoV-2 infection) infectious aerosols & can protect mouth/nose from impact of larger propelled wet droplets 1/

The degree of risk reduction is not great (see links), but some risk reduction is better than none.
😷cidrap.umn.edu/news-perspecti…
😷cambridge.org/core/journals/…
😷ncbi.nlm.nih.gov/pmc/articles/P…
2/

The @CDCgov now agree that cloth masks have a role-setting them apart from our public health bodies around the world.
cdc.gov/coronavirus/20…
3/

👉There have been interesting & innovative additions to cloth mask designs & inserts of late but these haven't been put through tests. They may be more effective than those in earlier studies. More funding of research & some direction might have better-positioned us for now.
4/

We know that presymptomatic and asymptomatic people have infectious virus in their upper respiratory tract & that such people seem to spread to new susceptible hosts. So eth risk is real.
😷nejm.org/doi/full/10.10…
😷link.springer.com/article/10.100…
😷jamanetwork.com/journals/jama/…
5/

So if nothing else, wear a mask in areas of known community transmission (the whole US?) because you will be upholding your end of the social contract by reducing the risk to others, from you, whether you are symptomatically ill or asymptomatically infected.
6/

Right now, the @who identifies virus-laden coughed & *exhaled* droplets & contact with droplet contaminated surfaces as the routes of SARS-CoV-2 transmission
😷who.int/news-room/q-a-…
7/

Definition of 2 reasons to wear a mask, as:
🥽source control - preventing an infected person propelling/exhaling virus-laden droplets
🥽personal protective equipment (PPE) - preventing an uninfected/susceptible person from becoming infected by an incoming virus-laden droplet
8/

We learned yesterday that surgical masks are effective for source control from droplets (>5 micrometres; µm) but not for all viruses (flu virus & rhinovirus RNA got out from behind the mask, hCoV RNA didn't) if emitted via an exhaled aerosol (≤5µm)
😷nature.com/articles/s4159…
9/

A nice example of droplet and droplet nuclei travel distances. An aerosol is a mix of heavier droplets and droplet nuclei and can be a confusing term.
😷ft.com/content/64ac88…
😷on aerosol terminology virologydownunder.com/flight-of-the-…
10/

From that image, you can see why 2m might be a better physical distance than 1 or 1.5m, but even that might still not be far enough apart for some viruses.
But also, think back-how often you see a completely uncovered/uninterrupted cough or sneeze?
11/

And further evidence supports that longer-than-traditionally-thought pathogen-bearing droplets travel via a turbulent puff cloud 7m to 8m; 1m or 2m don't; consider the high momentum puff cloud
😷jamanetwork.com/journals/jama/…
/12

We still don't have actual *evidence* for any specific transmission route but it's safe to consider close & prolonged contact with an infectious person, & contact with virus-contaminated surfaces as main drivers. Food, hair, pets are a bit of a distraction from these IMO.
13/

This close contact brings you within range of their droplets and aerosols and touch and its why physical distance - a primitive way of starting the virus of the human cells it craves - works. The CDC stress that distance is the No. 1 priority, above masks even, for the public
14/

The eyes are an overlooked topic among the public. I don't know why exactly. If eyes are a route to the airways, this mask debate is missing a big chunk of important.
So do we know much about eyes?
15/

Small studies have rarely found:
SARS-CoV-2 RNA in tears & conjunctival secretion in 1 of 30 COVID-19 cases
😷doi.org/10.1002/jmv.25…
2 of 72 COVID-19 cases with conjunctivitis had viral RNA detected in a conjunctival swab [🚨preprint]
😷medrxiv.org/content/10.110…
16/

Hypothesized as a route
😷thelancet.com/journals/lance…
We know from a primate study that ocular conjunctival inoculation resulted in RNA detection, infection and seroconversion [🚨preprint]
😷biorxiv.org/content/10.110…
So there *is* risk of infection via the eye
/17

Wearing a cloth mask will reduce the risk of contact between *some* of your respiratory mucosa (via mouth & nose) & virus-laden droplets/droplet nuclei. Some studies have suggested very little protection though
😷bmjopen.bmj.com/content/5/4/e0…
/18

Another aspect of reducing risk might be sealed eyewear and also face washing upon return from being outside of the home you should be *mostly* staying inside of.
Ensure using a mask doesn't cause a decline in distancing/hygiene activities. These are key preventatives.
/19

If you wear latex/vinyl gloves while out, realise you have added a surface on which virus is likely to last for *longer* than on your hands (perhaps only 30 minutes at most).
😷ncbi.nlm.nih.gov/pubmed/22264744
/20

And as with any PPE you choose to wear - be it masks, or gloves or Tyvek suit - dispose of them carefully *into* a rubbish bin. Don't leave them lying around for others to come into contact with, therefor putting *them* at risk. Then immediately sanitise your hands.
/21

See more detail from @CDCgov CDC at cdc.gov/coronavirus/20…

Images from who.int/emergencies/di…
/22

/23

/24