Post #585: Really, no kidding — shut up in public. Aerosol transmission of this disease appears possible.

Posted on March 30, 2020

Again, I’ll make this rare plea:  If you know someone in a position of responsibility that you think would benefit from reading this post, please pass this on.

Recall Post #573, where I talked about aerosol transmission of COVID-19 versus droplet transmission.  In particular, where I note that the issue is tiny “aerosol” particles (less than 5 microns) that can remain suspended in air, resulting in “airborne transmission” of the disease.  Versus droplets (larger particles) that rapidly fall out of the air, but can result in “droplet transmission” of the disease if you are near somebody who (e.g.) coughs, and a droplet lands on you (and directly infects you by (e.g.) landing in your mouth, or indirectly infects you because you, yourself, manage to transfer that material to your mouth/nose/eyes by touching your face.).

CDC advice to the public focuses primarily (perhaps, solely) on preventing droplet transmission.  That is, in large part, the theory behind social distancing.  Stay out of range, and don’t touch your face, and wash your hands.  A lot.

To which I added, and shut up in public.  Not for your benefit.  But for everybody else’s benefit.  Based on the potential for aerosol (“airborne”) transmission.  Because speech generates large numbers of aerosol (5 micron or smaller) particles.

Now go read this article.

Choir practice turns fatal. Airborne coronavirus strongly suspected

By Richard Read, LA Times, March 29, 2020, 7:34 PM.

From a single chorus practice with a 60 member chorus, where nobody was visibly ill, where they used hand sanitizer at the door, where nobody shook hands, or hugged — 45 have now tested positive for coronavirus.

In my Post #573 (Please shut up in public), I had this cryptic phrase, regarding a study that seemed to dismiss the potential for aerosol (airborne) transmission of COVID-19:  “But, you know, I’ll bet the hospitalized patients in those studies weren’t singing.”  That’s because I originally had a section noting that singing results in the release of huge volumes of droplets, particularly aerosol-sized particles. I was going to say, that puts the scenes of Italians singing to one another, in this epidemic, in a completely different light.  But upon reflection, given the gravity of the situation in Italy, I took that out.  Salt in the wounds, and all that.

In all likelihood, this Mount Vernon, Washington chorus practice was a “superspreader” event.  Likely, there was an asymptomatic-but-infected individual in that room who was a superspreader, likely because that individual was a “superemitter”, that is, an individual who naturally emits vastly more aerosol-sized particles than normal.  Search for those term in this very readable scholarly reference if you want to know more.

Singing generates aeorosol particles at the same rate as if you were coughing continuously.  And so, while those Italians were singing to each other, from the standpoint of aerosol transmission, it had the same effect as if they were all continuously coughing on each other.  That’s the section I took out of the last post, but that’s what needs to be said now.

And, likewise in this chorus practice.  From the standpoint of aerosol emissions, it’s as if they all stood around for an hour, in an enclosed room, and coughed continuously.

I now need to give citation as to source, the Nature: Scientific Reports linked above cited as follows:  “Similarly, Loudon and Roberts investigated the role of singing in the spread of tuberculosis and showed that the percentage of airborne droplet nuclei generated by singing is 6 times more than that emitted during normal talking and approximately equivalent to that released by coughing“.

The actual underlying research article cited there is quite old, and all I can get my hands on is the PubMed citation for that, and then a page of a .pdf reproduction (not searchable), located at this URL. The full article is behind a paywall, and I have other things to get on with.

But, from that article, it is worth nothing that, in fact, tuberculosis was documented to have been spread, in some circumstances, by singing.  I’ll hand copy the relevant passage here:

"Many circumscribed epidemics of tuberculosis have been described ... Characteristics and activities likely to lead to the dissemination of infection are not clearly understood, but in several reported instances (references), singing has been engaged in at the time that the transmission of infection appears to have occurred.

Bates and associates (reference) reported an outbreak of primary tuberculosis in an industrial school in which those in contact with an infectious person at choir practice showed a higher proportion of tuburculin "convertors" than those in contact with the same person during other forms of activity. These investigators suggested that singing might result in the expulsion of particularly large numbers of droplets with infective potential."

I believe that, increasingly, researchers seem to be waking up to the fact that aerosol transmission of COVID-19, in public settings (i.e., outside of a hospital room) is a possibility.  In Italy, there is now scholarly speculation that air pollution, in the form of a large level of fine airborne particulates, may potentially explain why some areas of Italy are so hard-hit.  The idea is that maybe the virus “hitchhikes” on these fine particulates.  (I have not read the underlying research, only the writeup in The Economist).  The area hardest-hit in Italy (the river Po valley) is known for high levels of particulate air pollution, and the day-to-day spread of coronavirus appears to correlated well with the level of particulates in the air.  (This, again, per the writeup in The Economist).

It is well worth noting that Wuhan has notoriously awful air pollution (citation).  And, New York City is not exactly the fresh-air capital of the world, when you get right down to it.

At this point, it is more than safe to say that the CDC’s description of how this is spread is, at best, incomplete.  The CDC continues to say that this is mainly spread by droplet transmission from symptomatic individuals.  (I.e. ,you’re close to somebody who is infected, who coughs, and one of the droplets lands on you.)  That may be true.  But I think a better wording might be “mainly, but not exclusively”.  I think that any reasonable person has to start to question the public-health aspects of certain group situations where likelihood of aerosol spread might be enhanced.  Starting from a chorus practice in a small room, and working back from there.

By report, there were no symptomatic individuals at that choir practice.  Maybe singing generates enough droplet-sized drops (versus tiny aerosol-sized drops) that this event could be attributed to droplet transmission, but I think that’s hugely implausible.  Droplets, by their nature, rapidly fall out of the air.  A single individual could not possibly have infected three quarters of a widely-spaced choir via droplet transmission.  We have to start considering that aerosol transmission is plausible.  And so I refer you back to my earlier posting.

Finally, as a further bit of epidemiological evidence, may I also say that, these days, there’s no way in hell that world leaders are being allowed within 6 feet of anyone who even remotely shows symptoms of COVID-19.  The idea that some staffer who is coughing and hacking would be allowed anywhere near the leader of a country is absurd.  And yet, a) typical incubation period for this is six days, and b) world leaders such as Boris Johnson have somehow managed to catch COVID-19, likely sometime in the past week.  For these individuals, droplet transmission by symptomatic individuals is a completely implausible explanation for how they caught COVID-19.  But I bet that guys like that are still spending a lot of time in face-to-face meetings, with lots of staff, in stuffy little meeting rooms.  Aerosol transmission by asymptomatic individuals is a far more plausible explanation of the facts.

The nice thing about scientific theories is that, if they are wrong, it only takes one well-documented event to demonstrate that.  I find it tough to look at this chorus practice, vis-a-vis the current CDC advice, in any way but that.  We can certainly continue to debate whether or not aerosol/airborne transmission of COVID-19 is common (outside of a hospital setting).  We can plausibly continue to say that it’s so unlikely that it does not and should not factor into public health advice.  But I think we can no longer reasonably debate whether or not it’s possible.

There is a simple piece of public-health advice that the CDC could offer.  Refer back to Post #573:  Please shut up in public.