
Covid-19 Superspreader Events in 28 Countries: Critical Patterns and Lessons - Symmetry
https://quillette.com/2020/04/23/covid-19-superspreader-events-in-28-countries-critical-patterns-and-lessons/
======
tzs
Way down in the article, it describes some data that was not included in its
analysis but nevertheless is quite interesting, where several people in a
restaurant were infected by one other patron.

This is something straight out of a TV crime show:

> As the authors note, the restaurant in question was air-conditioned on the
> date in question. Using video footage, they were able to chart the position
> of every diner in the restaurant, and then map their subsequent infection
> status in relation to both the single infected individual known to be
> present at the time and the air conditioning system’s outgoing and intake
> streams. If the primary transmission mode of COVID-19 were by small, sub-
> Flüggian airborne particles, the presence of the forced air convection might
> have made the environment safer (especially since “smear samples from the
> air conditioner [itself] were all [COVID-19] nucleotide negative”). But the
> researchers instead found evidence for the opposite: “The key factor for
> infection was the direction of the airflow,” with downstream individuals
> being most at risk—a result consistent with the thesis that COVID-19 is
> transmitted primarily through the ballistic transmission of large
> respiratory droplets.

I could easily imagine that having been a key insight in an episode of "Bones"
or "Elementary".

(If you are looking for something good to binge watch during COVID "stay at
home", I recommend "Elementary", currently on Hulu and CBS All Access. It's a
Sherlock Holmes set in modern times series. They did a really good job of
taking many characters and plots from the original stories and adapting them
in such a way that if you read the stories you will recognize them and perhaps
even think you know what is going to happen--but they have changed just enough
that the ending will still surprise you but also be eminently reasonable in
hindsight. The stories that aren't obviously based on any particular original
are equally good).

~~~
AnimalMuppet
Wait a minute.

> But the researchers instead found evidence for the opposite: “The key factor
> for infection was the direction of the airflow,” with downstream individuals
> being most at risk—a result consistent with the thesis that COVID-19 is
> transmitted primarily through the ballistic transmission of large
> respiratory droplets.

If the direction of airflow is the key factor, then the droplets have to be
moving with the airflow, and therefore _not_ ballistic.

Am I missing something?

~~~
derkha
I believe the reasoning is that aerosol would have ultimately spread
everywhere, including on the AC itself, while ballistics can be heavily
influenced by airflow, but are still limited in range.

~~~
uoaei
I think the definition of ballistic means that gravity is the dominant force
governing its path through space. So if it is "heavily influenced" by airflow
it is by definition not ballistic.

Then again, it's not aerosolized as it didn't diffuse homogenously into the
space. It's somewhere in between.

~~~
MereInterest
Eh, different fields can have different definitions for the same word, and
that's okay. If I tell a chemist that carbon is a metal, I would get a funny
look. If I tell an astrophysicist that carbon is a metal, it is perfectly
reasonable. Within the field of astronomy, metals are any element other than
hydrogen and helium. There may be a similar difference in definitions here

~~~
tricolon
For those who are curious, you can read more here:
[https://en.wikipedia.org/wiki/Metallicity](https://en.wikipedia.org/wiki/Metallicity)

------
excerionsforte
"Three of the SSEs—in Japan, Skagit County, WA, and Singapore—involved
concert-goers and singing groups belting out tunes together over a period of
hours. (The Skagit example is particularly interesting, because the organizers
were aware of the COVID-19 risk beforehand, and took the precaution of spacing
out the participants by several feet. If they had been merely chatting,
instead of singing, no one might have gotten sick.)"

Imagine how bad Austin would have been if SXSW had actually gone ahead given
how hellbent they were on going through with it. It would have been much much
worse state than it is now. It is a positive that the government listened to
health officials and shut it all down despite the complaining to the contrary.
Economies never work well in sickened environments.

~~~
uxhack
But the article goes on to say that "common human activity that aren’t
represented among these listed SSEs: watching movies in a theater, being on a
train or bus, attending theater, opera, or symphony"

But what I found interesting about the article (and it is long read) is his
hypotheses on mode of transmission. Which is the "direct ballistic delivery of
a large-droplet Flüggian payload from face A to face B" and that means that
interventions like the "expanded use of masks and social distancing is
critical" And we should also speak softly, avoid “coughing, blowing and
sneezing,” or exhibiting any kind of agitated respiratory state in public, and
angle their mouths downward when speaking."

But he does warn that he is a Computer Scientist rather than having any
medical background.

~~~
f38zf5vdt
The author seems to ignore the obvious confounding factor here of selection
bias -- super spreader events all seem to deal with people who are in the same
social circles rather than outside them, as would be the case in public
transportation, movie theaters, gyms, etc. The reason being that events with
people in social socials are readily traceable to an infected individual
attending, whereas contact tracing for anonymous infection in a shared area is
much more difficult.

Even diseases with low transmissibility are known to be disseminated by public
transit, such as tuberculosis.

[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4338233/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4338233/)

~~~
hammock
Interesting theory, why do you suppose a concert has more friends and less
strangers at it than an opera or symphony?

~~~
joshuahedlund
Well, I'd say there's a big difference between sitting silently in chairs at
an opera or symphony and standing/moshing/yelling loudly in extremely crowded
quarters at a rock concert.

~~~
DataWorker
A lot of coughing and high risk individuals at the symphony though,
unfortunately.

~~~
daotoad
High risk for mortality, yes. But are they higher risk for actually catching
the bug when exposed? I don't think anyone knows that.

I'm not even sure how you could come up with numbers on how much viral
exposure is needed to infect someone, short of controlled experiments with
volunteers. The odds of killing a few volunteers seems pretty damn high,
especially if you are testing with more vulnerable folks to establish a
differential estimate. That's not a study I'd want to be involved in on either
side of the clipboard.

------
barbegal
I think one of the things people over-estimate is how much evidence is used in
making public health decisions.

The UKs advice is to wash hands but not to use a face mask. Hand washing is
essentially free but the cost of producing reusable cotton face masks for
every single person would likely be ~ £1 billion. If that is money wasted, it
is still extremely small compared to the economic devastation which could cost
the UK government ~ £100 billion [1] and the economy as a whole significantly
more

[1] [https://obr.uk/coronavirus-reference-
scenario/](https://obr.uk/coronavirus-reference-scenario/)

~~~
heracles
The general evidence for washing hands as an effective counter-measure is very
very strong. It is a complete no-brainer, while decisions regarding face masks
are complex and have to take into account lots of variables.

~~~
barbegal
Can you point to evidence to back up your claim that "The general evidence for
washing hands as an effective counter-measure is very very strong."

Meta-studies show that the effectiveness of hand washing alone is minimal
[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4891197/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4891197/)

~~~
heracles
I think you misread me, I meant "general" as in general counter-measure, not
COVID19-specific. Clearly I should have been more precise. In a situation
where overload of healthcare is a primary concern, recommending counter-
measures against general infections (where hand hygiene qualifies) is a no-
brainer.

------
gns24
I'd been wondering why crowded public transport where people are breathing
right next to one another hasn't caused massive spreading. This explanation
makes a lot of sense - only when we cough or have to speak loudly do we exhale
a significant amount of droplets.

~~~
raiyu
Coronovirus has an rFactor of 2-3 and it is airborne, which requires droplets
from a host to come in contact with an uninfected person. But these droplets
travel to the air and then will collect on a surface. They will not stay
suspended in the air. Simply breathing next to a person who has the virus
isn't enough for transmission.

By contrast, measles has an rFactor of 17, because it is an aerosol. It is 6x
more contagious. And as an aeorsol, simply breathing next to a person who is
infected is enough for you to contract the virus.

Airborne is not the same as aerosol.

Put another way. If there is a person infected in a house hold with
coronavirus, not everyone is guaranteed to get it, because it is only
airborne.

If someone has the measles in a house hold, and there is no vaccine, then
everyone will get it, because it is an aerosol.

~~~
Izkata
> Coronovirus has an rFactor of 2-3

It's recently been revised up to 5-6 [0], and mortality estimates reduced.

[https://www.forbes.com/sites/tarahaelle/2020/04/07/the-
covid...](https://www.forbes.com/sites/tarahaelle/2020/04/07/the-
covid19-coronavirus-disease-may-be-twice-as-contagious-as-we-
thought/#6bb67c2729a6)

~~~
s1artibartfast
R0 is environment specific and this number should be taken with a grain of
salt.

The CDC paper [1] estimated that the R0 value may have been 5-6 in Wuhan,
during lunar new year, and before the public was ware of the virus.

Alternatively, the R0 value is now <1 in the US and the spread is decreasing,

[https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article](https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article)

~~~
ceejayoz
We don’t know the R0 in the US yet. We need widespread testing that we don’t
have to evaluate it.

Evidence out of NY today says it’s possible 14% of the state has already been
infected. That’d point to a pretty high value.

[https://www.wxxinews.org/post/random-test-finds-
nearly-14-ny...](https://www.wxxinews.org/post/random-test-finds-
nearly-14-nyers-already-had-corona-virus)

~~~
s1artibartfast
R0 is variable over time and describes the change in number of NEW cases.

IF new cases today are less than yesterday, the R0 must be <1 one incubation
period ago. That doesn't mean that R0 wasn't different a month ago, or will be
the same a month from now.

~~~
ceejayoz
> IF new cases today are less than yesterday

That's a big if. We don't have enough testing in place to determine that
currently. The reported number of cases and the _actual_ number of cases are
not the same right now.

~~~
s1artibartfast
We certainly have enough information now. You don’t need to know the total
number of infections to know the trend.

Positive cases have stayed roughly the same since April 4th while testing
increased. For R0 to be greater than 1, we would have to be worse at testing.

~~~
ceejayoz
Testing has not increased. Look at the chart here:

[https://www.cdc.gov/coronavirus/2019-ncov/cases-
updates/test...](https://www.cdc.gov/coronavirus/2019-ncov/cases-
updates/testing-in-us.html)

(Direct link: [https://www.cdc.gov/coronavirus/2019-ncov/images/lab-
specime...](https://www.cdc.gov/coronavirus/2019-ncov/images/lab-specimens-
tested.jpg))

We've been basically flat since mid-March.

~~~
s1artibartfast
Good point. I was mistaken.

I think the point still stands unless you think we are identifying a lower
proportion of infections

~~~
ceejayoz
> I think the point still stands unless you think we are identifying a lower
> proportion of infections

I do.
[https://www1.nyc.gov/assets/doh/downloads/pdf/imm/covid-19-d...](https://www1.nyc.gov/assets/doh/downloads/pdf/imm/covid-19-data-
map-04232020-1.pdf) indicates many areas of NYC are seeing more than 57%
positive results; that likely indicates we're not even scratching the surface.
We're simply not that good at identifying who to test.

------
londons_explore
I would like to think that in a global pandemic costing hundreds of thousands
of lives, trillions of dollars of economic costs, and significantly lowering
the quality of life of future generations, this research would have been done
months ago.

How hard can it be to find 100 similar workplaces, and to 33 of each say "You
guys must wear masks". "You guys must have all windows open all the time".
"You guys must wear gloves all the time".

Then wait 5 days, and see how infections spread.

That activity might lead to the deaths, in the worst case, of a couple of
workers. Yet the knowledge gained would save tens of thousands.

~~~
ebg13
We can accomplish many great things if we knowingly discard ethics for the
sake of efficiency, yes.

~~~
londons_explore
I question if modern ethics are perhaps too focussed of the wellbeing of the
individual, at the expense of the wellbeing of all of us...

Or, to put it more bluntly, a modern ethics committee would have rejected the
idea of installing sewers in cities to prevent disease because one builder of
the sewer might have died in the process. Without that, industrialisation
probably would never have happened, and we'd all be subsistence farmers today.

~~~
ebg13
> _Or, to put it more bluntly, a modern ethics committee would have rejected
> the idea of installing sewers_

You get to choose whether to be in the business of installing sewers. Saying
that it's ok to force people into medical experiments against their will for
the greater good is how you get Nazi holocaust atrocities. Medical ethics has
a long history that it sounds like you might enjoy spending some time reading
about.

~~~
buckminster
We're all being forced into a medical experiment against our will. Might as
well be a useful one.

~~~
ebg13
> _We 're all being forced into a medical experiment against our will._

I'm disappointed by your false equivalence between being told to stay home and
safe and being made into a guinea pig.

If being home and safe means you lose necessary income, then your ire should
be directed at your governments at all levels for refusing to prepare critical
safety nets and regulatory environments that would make it possible for you to
stay alive and safe without laboring every day. But advocating a regression on
everything that history has taught us about medical ethics is terrible and
bad. We're talking about thousands of years of accumulated and refined history
lessons here. Medical ethics is a perfect example of why learning history is
important.

~~~
buckminster
Might-have-beens have no relevance to the ethics of the choices we make now.
We are in the middle of a vast medico-economic experiment. It is bizarre to
consider the ethics of only the medical side of the experiment, not the
experiment as a whole.

~~~
rglullis
What "medico-economic" experiment?! This is much an experiment as "living in a
war-torn country" or "being hit by a major natural disaster" is an experiment.

If people start to starve because we stopped being able to produce food or
people start dying of other causes because our basic infrastructure start
collapsing, then you can start talking about ethical dilemmas.

~~~
jsight
> If people start to starve because we stopped being able to produce food or
> people start dying of other causes because our basic infrastructure start
> collapsing, then you can start talking about ethical dilemmas.

I think its a safe bet that this is already happening on small scales. Noone
is measuring the degree.

~~~
rglullis
Food insecurity already happens in many places around the world, even rich
countries. However, in those places it is an social-economical issue, not a
lack of labor/resources to produce the food needed for the population.

There may be images of long lines of unemployed people that have to get from
the government or food banks, but the food is still there. Farmers are still
producing, distribution networks are still working, essential services
operating. That part of the economy is still going.

------
clairity
i take this as a positive sign that the national conversation might be
starting to finally move beyond fear and panic to reason and understanding.

the primary mechanism of transmission (droplets into the nasopharangeal area)
has been known since at least february (when it started to become regular news
here in the US) and probably since at least december in china when it became a
known infectious agent.

the better we understand the situations and environments where transmission is
_materially_ increased, the faster we devise _reasonable_ mitigations and get
back to some semblance of normalcy.

it's also important to debunk false mitigations that only serve to mollify the
skittish (e.g., elaborate germophobic rituals) and thereby obstruct
understanding and cause other harms. in fact, some of those mitigations can
increase transmission risk simply by providing a false sense of relief (e.g.,
constant, but inevitably incorrect, mask usage).

~~~
andybak
> the primary mechanism of transmission [...] has been known

I thought the entire point of this post was that there were multiple competing
theories and little agreement or certainty? Your use of the phrase "has been
known" implies a broad consensus in public health circles. I've seen very
little consensus on any feature of this pandemic.

~~~
clairity
no, the point of the article was that while there are competing theories of
transmission, the centrality of the ballistic transmission mechanism has been
known for a while (from prior coronavirus studies) and has been relatively
undisputed as the primary transmission vector. to wit (from the article),

> "When do COVID-19 SSEs happen? Based on the list I’ve assembled, the short
> answer is: Wherever and whenever people are up in each other’s faces,
> laughing, shouting, cheering, sobbing, singing, greeting, and praying. You
> don’t have to be a 19th-century German bacteriologist or MIT expert in
> mucosalivary ballistics to understand what this tells us about the most
> likely mode of transmission."

------
SpicyLemonZest
Is it possible to test various mechanisms of infection on monkeys? Sprays at
various concentrations in their noses, in their mouths, on objects in their
environment. Seems feasible and useful, but maybe there are concerns about how
the results would generalize.

For extra credit, spray in their mouth through a basic cloth mask.

~~~
user_50123890
There are _humans_ who are currently volunteering to get infected by the virus
who would probably gladly participate in such tests.
[https://www.nature.com/articles/d41586-020-01179-x](https://www.nature.com/articles/d41586-020-01179-x)

~~~
SpicyLemonZest
And I'm one of them, but I'm not optimistic that human challenge trials will
actually end up getting approved. Medical ethics is a deeply, deeply
inflexible field even in the face of doom.

------
ra120271
When thinking about whether 2m social distancing is enough when coughs and
sneezes can travel viable infected virus much further, my understanding is
that governments care about onward transition rates. If on average an infected
person infects less than one other person it will eventually fade out.

So the question is does the 2m separation push the averages towards that? I
would think it does. Partly because the number of people within a blast radius
of a cough or sneeze is much lower, and secondly the probability of infection
drops with distance.

Social pressure that then drives coughing and sneezing people home in a social
distancing environment probably reinforces the effect of reducing transmission
rates.

Is it enough? That will have to be measured and analysed probably much later.

------
thedudeabides5
"It is theoretically possible that socioeconomically privileged individuals
really do lack some immune-response mechanism that protects individuals who
have been exposed to a wider array of infectious pathogens. (A recent report
on COVID-19 surveillance testing at a Boston homeless shelter contained the
stunning disclosure that 36 percent of 408 screened individuals tested
positive for COVID-19. Yet the vast majority were asymptomatic, and even the
few who were symptomatic did not diverge statistically from the 64 percent of
tested individuals who were COVID-19-negative.)"

Interesting. Having spent some time in SF, can attest that the homeless - on
occasion - appear to have super human immune systems.

~~~
AnotherGoodName
I wonder if it's the case that the filtering out of any risk factors has
already been done on the homeless population. Homeless people with marginal
health unfortunately don't live long. Those that have survived a long life as
homeless are very likely to be the most robust humans alive.

------
obelos
Yeah, but did they control for people with “Germanic foreheads”?

~~~
driverdan
You might want to explain this reference for those who don't know about
Quillette's support for eugenics.

~~~
obelos
I have a feeling the people downvoting me are already aware. Was downvoted
again after you posted your comment!

------
riccardobrasca
[https://threader.app/thread/1252581933835575297](https://threader.app/thread/1252581933835575297)

This is a super interesting point of view.

~~~
war1025
I read through most of that but will admit that I don't quite understand what
he was trying to get at. Can you summarize?

~~~
baq
it more or less says that people who get met a lot (...directed graph,
remember) somewhat counter-intuitively increase the total percentage of people
infected more than you'd expect even if they don't transmit the disease after
they contract it more than an 'average' person (again, directed graph).

~~~
war1025
I guess that doesn't seem counter-intuitive to me.

That's the whole reason behind social distancing right? To reduce the
likelihood that you will contract the virus from someone else. It's not so
much about keeping from getting other people sick, it's about keeping yourself
from getting sick.

As someone with young kids and a more frequent exposure to norovirus and other
stomach bugs than I'd like to admit, once that gets into the family, everyone
gets it. The way to avoid it is to not go places where your kid is going to
pick it up (public library usually), but in general you still go to those
places because they are convenient for other reasons.

I understand the focus on handwashing and sanitizing things, but that doesn't
do anything for direct exposure. If the stomach bug is near you, you're
getting it. I assume coronavirus is going to be much the same.

------
nl
This is a pretty good piece.

The work done in the restaurant paper is really good. It was a clever natural
experiment but clearly was a lot of work to piece together.

------
gdubs
For all my cynicism with politics, I was really impressed that the mayor of
Austin stepped up and forced the cancelation of SXSW. That’s an _enormous_
amount of money for the community, and it could not have been easy. Not a lot
of “lessons in courage” these days, but I really think that was one.

~~~
PeterStuer
"The community" receiving this money in each of these cases refers to a _very_
small percentage of the overall population of the region.

~~~
gdubs
I would bet that the _majority_ of small businesses in Austin bank on the
yearly spike in traffic, and that missing out on that is a very big deal.

~~~
Retric
Austin has more than 10x more people every day than attend SWSX which lasts
for less than 2 weeks. It’s even less significant as many people avoid the
area during big events. Perhaps a 5% increase in sales for under 3% of the
year so what 0.15% increase as a high estimate over the year.

~~~
giggles_giggles
According to this[1], SXSW brings Austin about $350 million annually.
According to Wikipedia, Austin's annual GDP is about $1.5B so 350/1500 =
roughly 23% of the city's annual GDP.

Anecdotally I know of many people who work year round to prepare for an event
at SXSW and rely on it for their entire annual income.

Cancelling SXSW is a big deal to this city. It hurts. It's not to be
downplayed.

[1] [https://austin.culturemap.com/news/city-
life/09-27-17-econom...](https://austin.culturemap.com/news/city-
life/09-27-17-economic-impact-sxsw-348-million-super-bowl/)

~~~
Retric
That GDP number is way off. 1.5B / 1 million people is 1,500$ per person.
[https://en.wikipedia.org/wiki/List_of_U.S._metropolitan_area...](https://en.wikipedia.org/wiki/List_of_U.S._metropolitan_areas_by_GDP)
Gives 146B in 2018.

That’s 350M number is also extremely suspect, at a minimum including existing
city residents as the hotel reservations are vastly below attendance.

Still even assuming that 350M was correct and not ridiculously inflated it’s
350/146,000 = 0.2%.

~~~
giggles_giggles
You're confusing GDP with GDP per capita, and also 350,000,000 / 1,460,000,000
= 0.23972602739 and to convert that to a percentage you multiply by 100 so you
get 23.973% as the result.

~~~
Retric
The number from wikipedia was 146 Billion (26 Austin-Round Rock, TX 146,784
metropolitan statistical area _in millions of dollars_ ) if you looked at the
link I gave. Which is 146,784,000,000, though you could argue the city is a
smaller area. Remember, thousand 3 zeros, Million 6 zeros, Billion 9 zeroes.

The GDP per capita was simply a sanity check showing how 1.4B must be wildly
wrong.

[https://en.wikipedia.org/wiki/List_of_U.S._metropolitan_area...](https://en.wikipedia.org/wiki/List_of_U.S._metropolitan_areas_by_GDP)

------
zzzcpan
_> If small-droplet airborne concentrations in unventilated spaces were a
common vector for COVID-19 transmission (as with measles, for instance), one
would expect whole office buildings to become mass-infection hot spots._

There is some logical fallacy here. Large droplets don't exclude aerosol
transmission, so you can attribute to it everything you attribute to large
droplets too. There are also such superspreading events of whole building
getting infected past lockdown, like the whole family dorm building getting
infected where people share bathrooms and such.

~~~
tomohawk
> It’s similarly notable that airplanes don’t seem to be common sites for
> known SSEs, notwithstanding the sardine-like manner in which airlines
> transport us and the ample opportunity that the industry’s bureaucracy
> offers for contact tracing. Yes, New Zealand has one cluster that’s based
> around an infected but asymptomatic flight attendant. But the many known
> infections he caused took place at a wedding reception, not in an airplane.
> This flight attendant was running what was, in effect, an unintended
> experiment, with the passengers on board his aircraft playing the role of
> control group. And the results offer a microcosm of the nature of SSEs as a
> whole.

