Both @CDCgov & @WHO are revising guidelines for wearing #facemasks. The US is well behind many countries, esp in Asia in rec'ing pop-based mask use. I agree w/ #Fauci that US should not mandate it, but there's much we can do to encourage mask use. What do we know? See thread. 1x

2x We know #facemasks were rec'd widely by govts, incl HK, S. Korea, Singapore, Taiwan, ECDC. Why was @CDCgov & @WHO so slow to act, esp when they had access to same sci info avail to other govts? What was the sci evi? Have there been new findings influencing @WhiteHouse?

3x What do we know about evi for #facemasks? Scant evi that masks protect healthy indivs from contracting #SARSCoV2. But reasonably good evi masks reduce risk of transmitting infection among indivs w/ #COVID19. Thus, if adopted as a pop-based strategy, it could reduce spread.

4x We've known #facemasks reduce #SARSCoV2 droplet dispersal w/ reduced transmission for some time. We also knew #COVID spread by asymptomatic indivs for some time. What we didn't know is the number of asymptomatic carriers, which we now believe could be up to 20% of infected pop

5x If sci says #Masks reduce spread, why didn't @CDCgov & @WHO say so clearly? Reasons not due to science, but to culture, economics & politics. Unlike Asia, US culture does not have a tradition of #facemasks, which is quite foreign to US pop. We're also ruggedly individualistic.

6x Perhaps most imp reason @cdc didn't rec #facemasks is b/c of potential hoarding & shortages in critical healthcare settings. We've sadly seen hoarding of foods, paper supplies & meds. It would be deeply concerning if mask use contributed to scarcity in hospitals.

7x Why is @CDCgov & @WHO now about to rec pop-based mask use? They have caught up w/ the evi, seen the need for more aggressive measures as #covid spreads exponentially.

8x What should @CDC/ @WHO rec now? #facemasks4all when out in public (shopping, hosp visits...). Beyond preventing #SARSCoV2 spread, #Masks are a potent symbol that #COVID19 is serious, stresses value of #PhysicalDistancing.

9x How can we encourage pop-based #facemasks in US? Starts from top down. PH agencies shd run ubiquitous pub service ads rec'ing #PhysicalDistancing & #facemasks4all. @POTUS & Cabinet should model good bhvr by wearing #Masks in public, also urging Americans to do the right thing.

10/10 We are all in this together. Let's appeal to our sense of civic responsibility: shelter in place, use #facemasks in public, don't go out while sick. We may be socially separated but we are not alone. We owe an ethical duty to each other to keep everyone safe. Be safe!