Covid-19 Superspreader Events in 28 Countries: Critical Patterns and Lessons

https://quillette.com/2020/04/23/covid-19-superspreader-events-in-28-countries-critical-patterns-and-lessons/

by Symmetry • 6 years ago

237 146 6 years ago

"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• 6 years ago

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.

klmadfejno4• 6 years ago

Just hypothesizing as well, but I think he might have it backwards. I'm not convinced you'll get magnitudes more virus in the ambient air from singing. But as a receiver if you're mouth breathing and taking deep breaths you're extra vulnerable. Nose hair is pretty effective

f38zf5vdt3• 6 years ago

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/

slg• 6 years ago

or exhibiting any kind of agitated respiratory state in public

The only sizable population of people that I still see out in public that aren't wearing masks are joggers. I wonder if and when we will put a stop to that.

malandrew• 6 years ago

This would also explain why many people are asymptomatic. They are still getting exposed but with a much lower viral load. Maybe the best "vaccine" here is just the lowest possible microdose of the coronavirus. We really should be looking at all the asymptomatic or low symptoms folks and figuring out what they have in common with one another. I would bet you it's just very low exposure, which gives the body more time to develop antibodies and mount a defense instead of the immune system being overwhelmed before it can adequately develop antibodies.

gowld• 6 years ago

If they had been merely chatting, instead of singing, no one might have gotten sick.

Really??

ceejayoz8• 6 years ago

It's entirely possible. Heavier breathing expels more droplets, and further.

SpicyLemonZest3• 6 years ago

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.

Symmetry3• 6 years ago

It would be illegal to do this with monkeys but ferrets have the same ACE2 protein we do and would be good candidates for this sort of research.

dboreham4• 6 years ago

Hmm...I swear I've read a paper talking about monkeys infected, having mild symptoms and then recovering. Perhaps it was a SARS-1 paper.

microcolonel• 6 years ago

Are any monkeys even susceptible to it?

SpicyLemonZest3• 6 years ago

I remember reading some study about monkeys reliably developing antibodies to it.

user_50123890• 6 years ago

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

SpicyLemonZest3• 6 years ago

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.

nl• 6 years ago

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.

londons_explore2• 6 years ago

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.

ebg133• 6 years ago

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

vikramkr2• 6 years ago

Not really in this case though. Ethically there's not much of a concern with that study since we don't know what works so we're not doing any harm by prescribing known bad methods. The ethical harm would come from a poor study design that won't tell us anything useful. Getting good data from a study like this is really difficult, and we can't really accomplish anything by discarding good data for the sake of efficiency

londons_explore2• 6 years ago

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.

klmadfejno4• 6 years ago

With 30 seconds of thought you are failing to control for:

* Social habits of the company

* Number of infected people within the company

* Compliance with the protocol

* Age demographics

* Infection rates from places other than the company

* Weird selection bias resulting from the company needing to not lock down to begin with

Very, very difficult study

dcolkitt2• 6 years ago

As long as the participants are randomly selected, all of those factors drop out into noise. The law of large numbers guarantees you that as sample sizes go to infinity, the magnitude in difference between the i.i.d. variables in the samples goes to zero.

macintux2• 6 years ago

We need, all of us, to stop focusing on deaths as the measure of how bad this can be. You're asking people to not only place their lives on the line, but even if that doesn't happen they face a significant risk of weeks of ICU care, followed potentially by a lifetime of respiratory problems.

jschwartzi2• 6 years ago

And medical bills!

vikramkr2• 6 years ago

It's not hard to tell people to do that. It is hard to get people to really comply and avoid changing behavior just by enrolling them in a study. It's hard to select 100 workplaces that are similar enough that they can be compared to eachother and also representative of the myriad complex types of social areas that people congregate in - opening a window might work in one type of office but not at all in another situation. And also, you need a control. You can tell a group of people to not change their behavior in a global pandemic to see what the impact of each intervention was. But getting people to comply? You even have problems in clinical trials where groups of patients find ways to get together and discuss side effects they've been having to try and figure out who has the placebo and who has the real drug killing the trial. Running statistically rigorous trials on that scale to get good information is just really difficult because of the study subjects.

Symmetry3• 6 years ago

I think part of the problem is that this doesn't fit neatly into any existing specialty. The "microscopic scale of nucleic acids or on the gargantuan scale of whole nations" both have very active research programs targeted at them, particularly the former. It's "the everyday face-to-face scale of inches and feet" that fails to have a scientific home.

dcolkitt2• 6 years ago

You don't even have to force people to behave one way or another.

You can skirt around the ethical issues by giving Sample A an unlimited supply of free masks, and keeping Sample B as the control sample. Even with free masks, not everyone in A will wear a mask. And some in B might still bring their own masks. But A will have higher mask use on average, and with large randomly selected populations you can tease out the impact using IV regression[1].

[1] https://en.wikipedia.org/wiki/Instrumental_variables_estimat...

rglullis3• 6 years ago

dboreham4• 6 years ago

This experiment has kind of been done: some countries had everyone wear masks. Other countries said "whoever told you to wear a mask is dangerously wrong, and even if you have a mask you can't wear it for fear of public shaming because we've told everyone that you're cheating healthcare staff out of their protection by doing so".

And then look at the infection spread in each country.

heavyset_go• 6 years ago

Let me know when you're volunteering to be a rat in this experiment.

_ea1k3• 6 years ago

All of us have already volunteered to be a rat in a global experiment of sorts anyway. I'm not sure why volunteering for three plausible paths would be bad. With this kind of study, self selection might even be ok.

gdubs2• 6 years ago

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.

PeterStuer2• 6 years ago

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

gdubs2• 6 years ago

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.

Spooky23• 6 years ago

Not necessarily.

There's a big halo effect on these sorts of things. When hotel rooms get booked, housekeepers get more hours, bartenders get more tips, restaurants get more covers, etc.

For the event itself you also have the carpenters who assemble the stages, security staff, garbage runs, etc.

enraged_camel• 6 years ago

This is extremely incorrect. A significant part of Austin’s economy is built on SXSW. Many small businesses here developed in tandem and cannot survive without it. Then there is the second- and third-order effects, such as those on contractors and freelancers.

soulofmischief• 6 years ago

Spend any significant amount of time in a tourist city and you'll find this isn't necessarily true. People plan their entire lives and balance sheets around these events.

dang• 6 years ago

(This subthread was originally in reply to https://news.ycombinator.com/item?id=22956128)

gns24• 6 years ago

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.

zaroth2• 6 years ago

What makes you think that crowded public transport didn’t pay a role in NY’s prevalence being so high?

standardUser2• 6 years ago

Public transit certainly didn't cause NYC-like levels of transmission in Japan, though it has a similarly dense public transit system.

standardUser2• 6 years ago

People tend to believe this virus is vastly more contagious than other airborne illnesses. It's certainly more contagious than the flu, by all accounts so far, but it's not even close to as contagious as measles. Simply walking by or standing next to an infected person almost certainly won't get you infected, unless they are actually coughing and sneezing in an indoor space (or directly at you).

ceejayoz8• 6 years ago

To be clear, it's not airborne. Measles is so contagious because it's airborne; SARS-CoV-2 is spread via droplets that fall to the ground fairly rapidly. It's a technical distinction, but an important one.

https://www.who.int/news-room/commentaries/detail/modes-of-t...

In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported.

(This is also a reason masks can be effective despite the virus particles being smaller than what masks can stop; you don't have to stop the particles, but the much larger drops they're contained within.)

raiyu• 6 years ago

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.

ceejayoz8• 6 years ago

https://www.who.int/news-room/commentaries/detail/modes-of-t...

In an analysis of 75,465 COVID-19 cases in China, airborne transmission was not reported.

"They will not stay suspended in the air" means it's not airborne. An airborne disease is one that does stay suspended in the air.

Izkata• 6 years ago

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...

mikeklaas• 6 years ago

You have the terminology backwards. Coronavirus is not (epidemiologically) airborne, but it can be aerosolized and transmit through the air.

tomohawk2• 6 years ago

Subways seeded C19 in NYC:

https://web.mit.edu/jeffrey/harris/HarrisJE_WP2_COVID19_NYC_...

jdm2212• 6 years ago

I tried reading the paper and it seems like as much an argument that "people get coronavirus at work and take it home on the subway" as "people get coronavirus on the subway and take it home"...? What am I missing?

obelos2• 6 years ago

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

driverdan• 6 years ago

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

obelos2• 6 years ago

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

tzs2• 6 years ago

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• 6 years ago

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• 6 years ago

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.

chasd00• 6 years ago

speaking of ballistics. i wonder, is there an easy way to increase the surface tension on these droplets? Maybe an inhaler or something that makes these droplets large and fall to the ground faster?

grok22• 6 years ago

Yeah, this explanation was messed up. Also, if you look at the graphic associated with this, it seems like people both upstream and downstream of the individual were infected and it is not clear if some of them had the infection simultaneously or were actually infected by the first person. Lots of questions here.

mattm• 6 years ago

That's almost exactly the description of a scene from the 90s movie "Outbreak" where Dustin Hoffman follows a vent in a hospital to learn that the virus is airborne.

creaghpatr• 6 years ago

Might even be where they got the idea.

andy_ppp• 6 years ago

So droplet size is very important for spreading then, implies wearing a mask will be quite effective at preventing you from contaminating other people...

riccardobrasca• 6 years ago

https://threader.app/thread/1252581933835575297

This is a super interesting point of view.

war10252• 6 years ago

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?

dboreham4• 6 years ago

I only read the beginning, but it seemed to be about transmission not being completely transitive.

baq2• 6 years ago

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).

klmadfejno4• 6 years ago

I think this thread does a terrible job of explaining its point. I've no idea if it's accurate, but the premise seems to be that people who are highly likely to get the virus do more to spread it than people who are likely to connect with many people conditioned on getting the virus in the first place, with acknowledgements that the two labels are likely to co-exist.

Just throwing it out there, I think this is likely going to be true, and the populations with higher proportions of old people are going to see greater infection rates than populations with fewer old people. That is to say, those who are vulnerable to the disease have a greater likelihood of getting other people sick than people who are naturally resistant to the disease but will behave irresponsibly. If you had a city with nobody over age 50, not only would the death rates be trivial due to the health of the population, but the spread of the virus would be very small.

I also don't think the views here hold once a non trivial proportion of the population is infected, like we have now, so it probably doesn't matter and is hard to act on anyway.

baq2• 6 years ago

it is interesting but it's also kind of common sense: of course people who contact a lot, whether they initiate the contact or not, are at risk. the thread gives some interesting results about models but epidemiologists, from what i hear, don't talk about superspreaders as in people but superspreader events which result in a lot of infected in a short time span. i don't think simple models like SIR capture these things at all.

thedudeabides5• 6 years ago

"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• 6 years ago

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.

tolstoshev• 6 years ago

Survivor bias. You're not seeing the dead ones.

zzzcpan• 6 years ago

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.

tomohawk2• 6 years ago

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.

barbegal2• 6 years ago

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/

Leherenn• 6 years ago

I think the reticence to promote masks is that there's not enough of them. It's getting better, but if a month ago they had said "everyone has to wear a mask" it would have been a panic as people can't get hold of them, plus it would have been harder to get some for essential workers.

If there had been massive stockpiles available, the message would have likely been different.

heracles2• 6 years ago

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.

barbegal2• 6 years ago

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/

clairity2• 6 years ago

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• 6 years ago

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.

macintux2• 6 years ago

The fog of war seems to be relenting, but as a casual observer it's been maddening to see so much conflicting information and the corresponding cherry-picking of information to assert that this is overblown.

clairity2• 6 years ago

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."

ra120271• 6 years ago

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.

Covid-19 Superspreader Events in 28 Countries: Critical Patterns and Lessons

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