Wisconsin's stay-at-home order had been relatively successful at containing COVID-19: when ranking US states by COVID-19 cases per million population, Wisconsin comes in 32nd. But Wisconsin still had more COVID-19 cases and deaths than South Korea, despite having a roughly 9-fold smaller population. Wisconsin is also still reporting about 300 new COVID-19 cases per day.
The mostly young people in the bar clearly are not worried about COVID-19 - they don't wear masks, and they are quite close to each other. Neither did the 29-year old in South Korea; so far, he seems directly or indirectly be responsible for at least 54 known cases. Health departments in South Korea have tried to track down 5,517 people who visited the same clubs so they can be tested for COVID-19.
Let's have a look at how exactly the people in the picture above might get infected by COVID-19, and what the likelihood is. Perhaps a few of them do have parents or grandparents that they would rather not pass the disease to, but they think they are safe "because numbers and changes of getting infected are low".
On first glance, about 300 new cases in a state with a population of almost 6 million does indeed sound like not much. But we know that anyone who carries the virus remains infectious for at least 10 days - that means we have at least 3,000 active cases in Wisconsin, and probably more. Many of these cases will have no or very light symptoms, but still be infectious.
Next, we need to take into account that not everyone who is infected gets tested. Looking at deaths and case numbers, we get a CFR of about 4%, which is at least four times higher than the known "correct" CFR of 1% or less. That gives at least 12,000 active COVID-19 cases in Wisconsin - at least one cheesehead in 500 is infected. There are perhaps 50 people in the bar, so the chances that an infected person is in the bar is about 10%. If we look at 10 open bars with 50 people each, changes that at least one bar is visited by at least one infected person are close to 100%.
Even given the 10% chance, our young bar goers might still feel safe, because the "stay away from anyone who coughs or sneezes". Apparently, they do not understand the words "asymptomatic" and "presymptomatic", or perhaps they just have not heard that multiple studies have shown that a very large percentage of COVID-19 infections can be traced to people without apparent symptoms. Or perhaps they simply do not "believe in science" (at least not until they go and visit a doctor).
A new scientific study shines a light on how COVID-19 transmissions in places like bars could happen. The study setup is simple enough to understand even after a couple of beers: speak into a black box; shine a laser light into the box to highlight droplets emitted when speaking; film this with an iPhone; and then count the droplets that can be seen in the video. The study found that one second of speaking produces about 2,600 small droplets. Loud speaking produces more droplets (but who would speak loudly in bars?).
Next, we need to do a little bit of reading and high school math. The reading can tell us how many corona virus particles can be found in saliva - on average, 7 million. The math can tell us the volume of a droplet, and thus how much volume is in all the droplet when speaking. It turns out that 25 seconds of loud speaking produces about 60 to 320 nanoliters of droplets. Multiply the numbers, and you see that one minute of speaking releases droplets with 1,000 to 5,000 virus particles. And that's for the average infected person - some patients have viral titers that are at least 100-fold higher than typical. They would emit at least 100,000 virus particles per minute of speech.
So if you are sitting in a bar for an hour to drink a few beers, a talkative infected person nearby may release anywhere between 30,000 and more than 3 million virus particles into the air. But what happens to the particles? "Classical" theory assumes that most droplets are large, and fall to the ground quickly - but it's largely based on what we can see if someone with a bad cold sneezes. This study estimated that most of the observed droplets were very small, and specifically measured how long they remained airborne. They report "exponential decay times of 8 to 14 minutes"; that means that a substantial fraction of droplets remain airborne for at least that long. Note that this was done in a sealed chamber without any air movement; in moving air, droplets can stay airborne even longer. The bars I have been to generally had some kind of air conditioning or at least fans that moved the air around - and moved any airborne, virus-containing particles around, too.
Unfortunately, we do not know how many virus particles you need to breathe in to get infected. In theory, a single virus particle could be enough, but in reality, the chance that a single virus can create a successful infection is probably small. But with every additional virus you breathe in, chances of infection increase. For various other viruses, fewer than 1,000 virus particles have been shown to cause infections in a high percentage of test subjects. If you are talking face-to-face with someone close to you, this number can easily be reached in a few minutes from interaction between breaths:
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| Breath interaction (from Villafruela et al, 2016) |
The big difference to the bars in Wisconsin is that Wisconsin won't have efficient contact tracing, and that any infection wave originating in bars will be able to spread much further.
Yes, I miss hanging out with friends for a few beers after a windsurf session. Very much so. But you certainly will not find me in a bar anytime soon.
Great article Peter, if not for the topic, you make the math of getting the illness simple and fun to read. Other than particles floating around for a few minutes, just the thought of individuals walking about in the bar and right into a load... PierreC.
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