Post #573: Please shut up in public, Part I

I’m going to wear a mask, from now on, on the rare occasions that I shop.  Despite CDC advice.  I’m also going to stop talking when shopping.  This post outlines why.  A subsequent post will give details.

I have never said this on any prior post, but if you know somebody in a position of influence who you think might benefit from seeing this, please pass this post on.


I have been trying to resolve a few things about coronavirus that have been puzzling me.  In particular, there appear to be fairly important inconsistencies between:

  • What the CDC says about the likely transmission route for the disease.
  • What the CDC says about the need to wear a mask in public, and, in particular,
  • The continued spread of the disease despite social distancing.

Here’s the issue.  The CDC (and pretty much everybody else) says that droplet transmission from symptomatic individuals is the principal way that the disease is spread.  In plain language, you’re in range (less than 6′ away) when someone who has COVID-19 coughs or sneezes.  That’s how they think this is mainly spread in public spaces.  (Just read the CDC page referenced above.)

And then, much iffier, and far less importantly, touching surfaces where those droplets landed or actually physically touching the skin of an infected person (e.g. shaking hands).  Experts literally say there have been no known cases of transmission via food or food packaging (via Serious Eats, showing citation as to sources from CDC, USDA, and (particularly readable) the European Food Safety Authority)  Finally, fecal-oral transmission appears to be rare to the point of irrelevance for members of the public.

But — read Post #565 and others here — my impression is, these days, a) nobody who has symptoms is stupid enough to go out in public, and b) nobody is so much as clearing their throats loudly in public, and c) everybody is keeping their 6′ social distance in public.

What you see in the video above — that’s a heavy-handed illustration of droplet transmission.  But you just don’t see that in public spaces these days.  Or, at least, I don’t.

So, why does the disease continue to spread?  By this time, those who contracted it in a public space, prior to widespread “social distancing”, ought to have shown up in the statistics.  (Or, at least, that’s my calculation, in prior posts — median six days incubation, median four days for testing.)  Is that calculation wrong?  Or are people routinely violating the social-distancing conventions?  Or is the preponderance of growth in case counts now from private-space (within-family) disease transmission?  (On that last one, I could not find anyone who says that, so, I’d have to say no. Although, per the WHO report I discussed in earlier posts, the tail end of the spread in China was, in fact, characterized as largely being spread within family units.)

So the key technical question is, why are we seeing continued high rates of disease spread in the (plausible) absence of droplet transmission from symptomatic individuals in public spaces? 

I’ve finally found an expert who has noted the same inconsistency from CDC, and has published a plain-language writeup of it.  That’s “COMMENTARY: COVID-19 transmission messages should hinge on science”, Lisa Brosseau, ScD, posted 3/16/2020 by the University of Minnesota Center for Infectious Disease Research and Policy, available at this URL.

I think everybody who wonders how this disease is spread should take a look at that.  I’m going to summarize a few key points here, and do a separate post with the details.

Briefly, the key question is whether “aerosol transmission“* is a significant factor for COVID-19, as opposed to “droplet transmission”.  And the experts say … it’s not quite clear.  I guess I would characterize this as “the experts say no … mostly … for John Q. Public”.

* Aerosols are tiny, invisible particles, typically characterized as being under 5 microns in size.  That’s in contrast to “droplets”, which are particles bigger than that, some of which are visible.  What you see, in the video above, that’s droplets.

But if (emphasis if) aerosol transmission is even plausibly a factor in public spaces, then there is a key piece of simple public-health advice which the CDC may need to consider:  Shut up.  Literally, don’t talk in an enclosed public space (store, office, factory).  Or if you talk, talk softly.  Because when it comes to generating aerosol-size particles, it appears that talking generates them at a rate comparable to coughing and sneezing.  (And if you read nothing else in that reference, search for and read “superspreader”.)

I want to be clear:  The preponderance of epidemiological evidence (and a smattering of other evidence) still suggests that COVID-19 does not routinely spread via aerosols, in public spaces.  (See this reference for what looks like a pretty thorough discussion.  Aerosol spread is known (?) to occur through prolonged exposure, in an enclosed space, with a symptomatic individual, but that’s an issue for hospital workers, not for the rest of us.)  But, you know, I’ll bet the hospitalized patients in those studies weren’t singing.   I’d be willing to bet they weren’t talking loudly.  (See the “talking generates” reference above.)

Likely, “shut your mouth” will never be official CDC advice, for a couple of reasons.  One being, they are firmly on record saying that aerosol transmission is unlikely.  The other being that nuisance masks don’t stop aerosol-sized particles.

That said, given how iffy this whole thing is, I think that if you’re in an enclosed public space, you need to keep your mouth shut.  Speak softly, if at all.  Not for your sake, but for the sake of others.  It costs you nothing, and it might help.

So I’m adding that to my personal shopping hygiene regimen (Post #568).  And I think I’m going to wear a mask on the rare occasions when I shop, from now on.

Three final points for this summary.

First, every kid knows what “say it, don’t spray it” means.  But in fact, visible droplet emissions are rare in normal speech.  That’s not to say that they don’t occur when people talk loudly (and here I went looking for a picture I know I have seen, of a Shakespearean actor, backlight, basically spraying the audience, but I could not find it.)  But normal speech does, in fact, routinely generate some droplet-size particles (above 5 microns, see middle graph, Figure 2, in this reference).  Just not very many, I think.  Hence, I think, the CDC emphasis on coughing and sneezing.  That said, the creation of some droplet emissions in normal speech is yet another reason to keep your mouth shut and talk softly if you must talk.

Second, I will now point out the inconsistency in the CDC advice.  If public-space droplet contamination remains the main transmission vector, why aren’t we all wearing (some sort of cheap) masks?  The CDC literally says not to wear a mask unless you are sick.  But masks — even cheap masks — reduce droplet emissions.  (That’s why the CDC does tell you to wear one if you are sick).

Finally, a related speculation is:  I wonder if the great success of all the post-China developed Asian countries, in containing this epidemic, is due in part to their well-established high propensity to “mask up” in public.  It caught China by surprise.  And sure, the rest were quicker to jump on the social distancing bandwagon and to implement other effective public health measures.  Probably more effective at it, too, than we have been.

But we, the public, keep thinking of masks as a way to protect ourselves.  CDC has told us, no, cheap masks (i.e., surgical masks, dust masks) are not a way to protect yourself.  But what if (cheap) masks are really a way to protect everybody else from your inadvertent droplet emissions?  Granted, an unproven and possibly only marginally effective way.

But even with those huge caveats, maybe we all ought to be covering our mouths when in enclosed public spaces.  (And, I think, but am not sure, that any cover is better than no cover, for preventing droplet emissions, meaning, I don’t think you even need a mask, per se, for this).

And keep your mouth shut.  That’s my advice.  Not for your benefit, but for the benefit of others.

I hope to fill in the details in subsequent posts.