It’s the talking, my God, it’s the talking (and yelling!)

Last week I said to my friend, fellow Political Science professor and Covid-obsessive, Kyle Saunders, “you know, I really think a majority of the transmission is coming from people in the 24 hours before they show symptoms just by talking.”  Now, I think that more than ever.  Talking is at the essence of humans as a social animal and I really think that is what this little particle of RNA has hijacked to make itself so contagious (that, and actually be highly contagious before symptoms begin).  We’ve heard so much about the virus being spread by coughing and sneezing, but those are, obviously symptomatic when people are cognizant of the risks and self-isolating.  And, the evidence suggests there’s just not all that much virus being spread from ordinary breathing.  But talking– and especially yelling, shouting, singing– and there you go.  We know that time after time churches have been outbreak epicenters– plenty of talking and lots of singing.  We’ve seen a soccer game in Italy as an epicenter (hello, shouting!, even if outdoors), and the best evidence is a very modest amount of surface transmission.  One of the famous South Korea studies in an office building with a ton of transmission (almost all on the same floor), was literally a call center.

We always hear that sporting events should be about the last to re-open, and I agree.  But, also, damn, bars are so risky.  One of the reasons I hate going to bars is that they (most of the ones I have ever ended up at) are so loud you literally have to yell inches from a friend to be heard.  Talk about a massive viral load right in your face.

I had meant to link to this Drum post to talk about the fact that (please, hopefully!) it’s really not so dangerous to open schools.  But, for present purposes, check out restaurants (which includes bars– I checked in the study) in this graph:

So, I’ve been thinking all this when along comes this Science Magazine article which I have found the most interesting and impactful since that great Erin Bromage post.  Seriously, just read it all.  But, hey, because that’s what I do, my favorite parts.

First, this amazing statistic on the contagiousness that people who know me will almost surely get sick of hearing from me:

Most of the discussion around the spread of SARS-CoV-2 has concentrated on the average number of new infections caused by each patient. Without social distancing, this reproduction number (R) is about three. But in real life, some people infect many others and others don’t spread the disease at all. In fact, the latter is the norm, Lloyd-Smith says: “The consistent pattern is that the most common number is zero. Most people do not transmit.”

Yep.  Just pause and think about that.  The typical person who contracts Covid spreads it to 0.  Of course, for those that do spread– watch out.

That’s why in addition to R, scientists use a value called the dispersion factor (k), which describes how much a disease clusters. The lower k is, the more transmission comes from a small number of people. In a seminal 2005 Nature paper, Lloyd-Smith and co-authors estimated that SARS—in which superspreading played a major role—had a k of 0.16. The estimated k for MERS, which emerged in 2012, is about 0.25. In the flu pandemic of 1918, in contrast, the value was about one, indicating that clusters played less of a role.

Estimates of k for SARS-CoV-2 vary. In January, Julien Riou and Christian Althaus at the University of Bern simulated the epidemic in China for different combinations of R and k and compared the outcomes with what had actually taken place. They concluded that k for COVID-19 is somewhat higher than for SARS and MERS. That seems about right, says Gabriel Leung, a modeler at the University of Hong Kong. “I don’t think this is quite like SARS or MERS, where we observed very large superspreading clusters,” Leung says. “But we are certainly seeing a lot of concentrated clusters where a small proportion of people are responsible for a large proportion of infections.” But in a recent preprint, Adam Kucharski of LSHTM estimated that k for COVID-19 is as low as 0.1. “Probably about 10% of cases lead to 80% of the spread,” Kucharski says. [emphases mine]

That could explain some puzzling aspects of this pandemic, including why the virus did not take off around the world sooner after it emerged in China, and why some very early cases elsewhere—such as one in France in late December 2019, reported on 3 May—apparently failed to ignite a wider outbreak. If k is really 0.1, then most chains of infection die out by themselves and SARS-CoV-2 needs to be introduced undetected into a new country at least four times to have an even chance of establishing itself, Kucharski says. If the Chinese epidemic was a big fire that sent sparks flying around the world, most of the sparks simply fizzled out.

As to that last point, Nate Silver has frequently speculated that when we look at patterns of outbreaks, there may very well be a significant stochastic component and it does seem that the lower this k value the more likely purely random bad (or good) luck may play a role.

And, let’s return then, to the original subject of the post– vocal communication:

Some situations may be particularly risky. Meatpacking plants are likely vulnerable because many people work closely together in spaces where low temperature helps the virus survive. But it may also be relevant that they tend to be loud places, Knight says. The report about the choir in Washington made her realize that one thing links numerous clusters: They happened in places where people shout or sing. And although Zumba classes have been connected to outbreaks, Pilates classes, which are not as intense, have not, Knight notes. “Maybe slow, gentle breathing is not a risk factor, but heavy, deep, or rapid breathing and shouting is.”

Yep.  So, seriously.  Talk less and talk less loud.  I was fascinated to learn after reading this that Japan’s campaign, all along, has literally discouraged talking in close quarters:

COVID-19 State of Emergency – eSolia Inc.

Of course, there’s more research to be done and plenty we still don’t know.  But, I think it is fairly safe to say that we need to be extra careful indoors where people are talking to each other and the longer and louder the talking the greater the risk.

About Steve Greene
Professor of Political Science at NC State

3 Responses to It’s the talking, my God, it’s the talking (and yelling!)

  1. jeffbc94 says:

    But I have to talk loud to be heard through my mask!! 🙂

  2. John Willingham says:

    Excellent post.

    On Wed, May 20, 2020 at 3:43 PM Fully Myelinated wrote:

    > Steve Greene posted: “Last week I said to my friend, fellow Political > Science professor and Covid-obsessive, Kyle Saunders, “you know, I really > think a majority of the transmission is coming from people in the 24 hours > before they show symptoms just by talking.” Now, I think ” >

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