Part 2 - How Does the Virus Get Into the Air? - The Science of COVID-19 Safety for Coffee Businesses
While we were measuring the impact COVID-19 has on the Specialty Coffee industry during our recent survey project, one clear fact came through: understanding COVID-19 science and safety is key in order for coffee businesses to survive.
Here we share How Does the Virus Get Into the Air? - Part 2 of The Science of COVID-19 Safety for Coffee Businesses. This second segment includes a comparison of the science of COVID-19 airborne transmission and how it arrives in the air (and how this is measured) while also debunking some misleading information.
This part and the rest of the video features Professor William D. Ristenpart of the UC Davis Coffee Center, a chemical engineer in “transport phenomena,” meaning that he studies transport—fluid mechanics and aerosol science. Aerosols are suspensions of small solid particles or liquid droplets in the air and is therefore very relevant to COVID-19 transmission. Prof. Ristenpart has published many articles in prominent scientific publications on COVID-19 transmission and prevention. He is also a coffee scientist, who has worked with the SCA on a number of research projects. With this background, he’s well-equipped to share information over respiratory virus transmission and what coffee businesses can do to keep their venues safe.
Prof. Ristenpart will address coffee houses and food retail concerns related to COVID-19 and steps businesses can take that are based in science, to prevent the spread of the virus through four actions: masks, ventilation, air purifiers, and limiting exposure.
A Live Q&A with William D. Ristenpart will follow the video on Thursday October 15 at 8am PDT/4pm BST.
Full Transcript (Part 2)
Okay, welcome to part two of Coffee Houses and COVID-19. And so the theme of this part is, how does the virus get into the air? Alright, if we're thinking about airborne disease transmission, that's a really crucial question.
Here on this slide, what I'm showing are several pictures of media representations of airborne disease transmission. And so I've already mentioned in part one a couple of these pictures on the top right here. Is that a great editorial by Linsey Marr about the coronavirus being in the air. And there's a picture of a fellow sneezing into a handkerchief. Up on the top-left is another tremendous article by Shirley Miller. And again, the picture there's somebody sneezing. In general, if you Google for images of Covid 19 and airborne, you're going to find lots and lots of pictures of people sneezing. And for whatever reason, they're almost always sneezing from left to right. And the vast majority of them are male. I'm not going to comment on that. What I'd like to really point out here is that these pictures are extremely misleading about the threat of airborne disease transmission. And so why is that?
1:11 Myths About Airborne Disease Transmission
I'm going to give you three reasons why they're misleading. And so the very first reason is that sneezing isn't even a symptom of COVID-19. So here on the right is a chart of all the typical symptoms of COVID-19 compared to other diseases like the common cold and the flu and Covid 19 in particular, it's a respiratory pathogen. It infects your respiratory tract. Fever and dry cough are by far the most prevalent symptoms. Okay. If you look down here at the bottom, sneezing is not even a symptom. It's less than rare. Ok. And so it's very misleading to always, when you're talking about Covid 19 and airborne disease transmission. To always show a picture of somebody sneezing when that's not even the main symptom. It's kinda like if every time somebody with a broken leg was mentioned in the media, they showed a picture of somebody riding a mountain bike, right? Yes. You can get a broken leg from riding a mountain bike, but that's not the only means by which somebody breaks a leg. Same thing with COVID-19. Okay. So that's the first reason why those pictures are misleading.
The second reason is that people without any symptoms at all can transmit COVID-19. And that's one of the main reasons that it spread so quickly. There are so many people who are asymptomatic or pre-symptomatic spreading it. And just to really drive that point home, here is something called an epidemiological chart. And what this does is it lists several different patients associated with an outbreak.
This happened to be a church in China. So the index cases are patients a1 and a2. Those are the ones who spread it to the other ones during this particular outbreak. And they were believed to have been infected somewhere on January 18th. On January 19th, they went to church. And the key thing here is that these two index cases had no symptoms, no symptoms when they went to that service. And they didn't have any symptoms for three to five entire days after exposure. But so even though they were not symptomatic, patients, a3, a4, and a5 who went to the same church on the same day, got infected. And so these exposed individuals developed symptoms four to 15 days after exposure. And very intriguingly, patient A5 wasn't even in the church at the same time. But happened to sit in the same seat as one of the index cases? And so that's a really key thing you can be talking with. Somebody looks perfectly healthy, not coughing, not sneezing. But they're, they're transmitting the virus and they're infecting other people. And so there's been a lot of great epidemiological research to try to figure out how many people are transmitting without symptoms versus who do have symptoms.
And here the highlighted on the slide is some work by Jeff Shaman to Columbia University. And according to his modeling, somewhere close to 86% of transmissions come from people with mild, limited or no symptoms at all. So now you might be thinking, well, wait a second. If the infected individuals aren't coughing or sneezing. That's what it means to not be symptomatic. How does the virus get into the air? And so one potential answer is simply by breathing and talking. And the fancy word for all these things is expiratory activities.
4:30 What is Expiration?
Expiration is the fancy word, that means air coming out of your respiratory tract. So breathing and talking, how does that get virus into the air? Well, we know that this can happen because we can measure it. So here on the slide I'm showing some images taken from some of my own group's research. So on the left is a cartoon schematic of a characteristic or representative setup. We have an individual breathing or talking into a funnel connected to something called an aerodynamic particle sizer. And that's a fancy sophisticated piece of equipment that has a bunch of lasers inside. Long story short, it can measure very small particles that you can't see with the naked eye.
And so there in the middle is a picture of my graduate student, Dr. Sima Asadi, doing some experiments by talking into that funnel. And other people do this up on the top right. There's some work by Jonathan Reid in the UK. He actually has had people singing into an APS. On the bottom right. That's a fellow named Don Milton at the University of Maryland, College Park. He's got a really big funnel and he's actually got it connected to a bioaerosol sampler that not only can count expiratory particles, but can also measure viable virus that's carried in them. And so, to show a little bit of representative data here again is some work by my grad student, Dr. Asadi. And on the left where you're showing, what we're showing is a graph of how many particles come out per second, okay, as a function of different types of expiratory activities. And on the left are various modes of breathing. And you can see nose breathing is very small. Mouth breathing a little bit more deep, fast and fast, deep, or whether you inhale quickly and exhale slowly or vice versa.
6:16 Different kinds of Expiration
The key point here is that breathing and it's a little bit, but speech emits actually a tremendously larger number of particles. And so here on the right and the kind of reddish zone, we have quiet speech, intermediate speech, or really loud speech. And you can see that the louder you are, the more particles that come out. On the far right, we have a graph that shows the number of particles coming out and the characteristic size of these particles.
6:45 Let’s Talk About Particle Size
So I mentioned a second ago that they're too small to see with the naked eye. And the horizontal axis here, that's the diameter of the particles and it's measured in something called microns, micrometers. And you can see that the peak of these distributions, regardless of how loud you are, it's somewhere right around one micron. That length scale is really important because it drives home The third reason why all those media pictures of people sneezing is very misleading. And so here's a cartoon that I've shown a couple times. This came from a recent article published in Science by Kim Prather and colleagues. And it's a great cartoon, but it's also misleading.
And so here's this cartoon to show somebody talking, and you see this very scary-looking cloud of huge red droplets being emitted. Okay? And so this is what it looks like in cartoons. And what I'd really like to emphasize is that here's what it looks like in reality. In reality you see somebody talking, you don't see any particles, or hardly any particles at all. And if you do see something that's very rare and that's not even an aerosol particle. The fact that you can see it means it's very large, relatively speaking. And so the key point here is that almost all of the expiratory particles emitted by breathing and speech are way too small to see with the naked eye. And so to really drive this point home. Here on this slide, I have a couple images of something that you know about. Here is on the left is the cross section of a human hair, presumably was from somebody with brown hair. And so on average, the diameter of a human hair, somewhere around 1 tenth of a millimeter. That's equivalent to 100 microns.
Over here on the bottom right, you can barely see it. But if you look carefully here is, to scale, a characteristic one-micron expiratory particle. And so you can see it's, it's so tiny, you can barely see it compared to the diameter of a human hair. If we zoom in on this one micron expiratory particle, here, I've now magnified it. Okay, we can see here it's one micron. And what I really like to drive home is that even though these particles that you're breathing and speaking out are too small to see with the naked eye, They themselves are huge compared to the virus. So this little red dot represents, to scale, the diameter of SARS-CoV-2, which is the virus that causes COVID-19. It's only about 0.1 microns, which means you can literally fit about a 1000 of these virus particles in one 1-micron diameter, expiratory particle. And so you might be wondering about my color choice here. Why did I show this expiratory particle? It's kind of an ugly yellow color, right? Shouldn't it be blue or something because it's liquid coming up. And the reason for that is it's very intentional my color choice there because what are these expiratory particles made of? They're not just water.
9:45 Your Respiratory System
The fluid that lines your respiratory tract is composed of lots of different proteins and salts, which are what a scientist refer to as non-volatile. It means they don't evaporate. So yes, inside your body, all of the respiratory fluid has lots of water. But these droplets, as soon as they're emitted out into the air, they very rapidly within fractions of a second. Evaporate all the water leaves, and it leaves behind all the non-volatile stuff, basically the mucus, alright, the dried proteins and salts and the virus hangs out in there as well. And so to really illustrate how these expiratory particles form, here on the left, we have a schematic of the human respiratory system, okay?
And there's basically three places where these particles can form. And starting up at the top. The one that probably most people think of is the so-called oral mode. Sometimes when you talk, you do have spittle, you can see large droplets that are emitted. You might've heard expression "say it, don't spray it", right? That those are, the fact that you can feel them and see them means relatively speaking, they're huge, way bigger than 30 microns, maybe up to even millimeter scale, right? And so that's the so-called oral mode is formed mostly saliva from your mouth.
What most people don't realize is that you can also form expiratory particles in other places. One place is deep in your lungs. There's something called the bronchioles. And there the respiratory fluid, the lines, the little channels where oxygen and carbon dioxide exchange in your lungs. When you inhale or exhale, those channels expand or collapse. And when they do that and when they pinch off, they can effectively form little droplets that then get exhaled. That's the second place. The third place is right here in your vocal chords. Okay? And so what I'm showing here is a certain type of video called stroboscopy, where they use flashing lights and they are looking right at your vocal chords. And so when you say, "Aaaaaah" what's actually happening inside of your larynx, inside of your vocal cords, is there's a couple little flaps that are going back and forth like this very quickly. Okay.
12:10 The Vocal Chord Connection
So I have a kind of a deep voice. The frequency is about a 120 Hertz, which means that when I say my vocal cords are doing this a 120 times per second, it's very fast, blah, blah, blah, blah, blah. Here's a video. And to me it looks kind of like a little alien. But that's, this is just a healthy human. Women, right? And it's not showing it in high-speed. This is again, is flashing lights, but hopefully you can see that these vocal folds are going like this very quickly. And there at the bottom you can see a little cartoon of what happens, the fluid that's lining the vocal chords. And it's creating these little droplets that are then exhaled out into the air.
And so I think a lot of people are unaware that just talking causes these particles to be emitted. You can't see them. A lot of people, have never seen a video, vocal folds or vocal cords doing this, right? But it's very well established in the scientific literature that this happens at these droplets are emitted. So I mentioned that if asymptomatic people are not spreading it by coughing or sneezing to a great extent. It might be breathing. I might be speaking like I'm showing here via vocalization. Just to really complete the picture, going back to another mode of aerosolization of virus. But I'll just very briefly mention that there are other ways that have nothing to do with expiratory activities, nothing to do with breathing or speaking. How they'll get into the air. And I mentioned this idea of aerosolized fomites, which is a fancy way of saying contaminated dust.
And so this is some work my colleagues and I did very recently. On the left is a video of my student holding a Kleenex, a contaminated Kleenex, and she just rubbing it gently by hand. And she's holding it in front of an aerodynamic particle sizer. And so this video on the right, this shows the number of micron-scale aerosol particles emitted by this Kleenex as a function of time. And you can see that when she stops moving her hand, the particle count goes towards 0. And then she starts crumpling it. It shoots up again, and then she stops and it goes down. So there are tremendous... Again, people don't think about it because you can't see it. This is not dust that you can see floating around in the air. This is micron-scale, particulate matter that you can't see. Something like rubbing a contaminated Kleenex launches thousands of particles into the air.
And our other research, which there's a great Wired article here about this, which you can read if you're interested, shows that at least for influenza, these contaminated dust particles can carry the viable virus. That research was with influenza. Here on the right, I'm showing a couple of recent articles, specifically about COVID-19.
Up on the top right. There's some work by Liu et al, where they went around sampling hospital air in China. And surprisingly they found some of the greatest airborne concentrations of SARS-CoV-2. Were not in the patient rooms, but were in the rooms where the healthcare workers were taking off their personal protection equipment, taking off their masks, taking off their gowns. And they hypothesized that maybe that's consistent with the virus being aerosolized on the dust when you take off a shirt. Okay? Or if you just go like this and rub your sleeve, you can't see it. But there's a lot of stuff being launched into the air. And if I sneezed into my shoulder there, potentially that'd be getting the virus in the air.
And here on the bottom right, there's another recent report where they went around and sampled with swabs, different surfaces in a hotel room or a couple of hotel rooms known to be occupied by people who had been infected with COVID-19. And they found some of the highest concentrations of the virus on the pillowcases and on the duvet cover and the sheets of the bed that they slept in. And it's known from other research at least with influenza and other things like that that simply shaking a blanket, for example, can launch virus into the air.
16:18 Takeaways About Vocalization
So to summarize part two, how does the virus get into the air? I want to emphasize that we don't know for a fact, we don't have any direct evidence for any particular mode of airborne disease transmission. But there's a lot of indirect evidence suggesting that if you look around a cafe, what are the things that you most need to worry about? That one I would worry most about. And I made the picture here big to represent that is vocalization. People talking, people, speaking, people singing, even breathing. Those can potentially be the biggest source of transmission from asymptomatic people. Now that doesn't mean that you should worry about these other means. Clearly, if somebody coughs in your face or sneezes, they're also emitting lots of, not only big droplets that you can see but also small expiratory particles. So I'm not trying to say, don't worry about coughing, of course, that's a big concern.
And I also mentioned this idea of re-suspension of dust. That's also a potential mode of transmission. There's not a lot of science on that yet, especially for SARS-CoV-2, but it is also a potential area of concern. Okay, that brings us to the end of part two where we talked about how the virus gets into the air in the first place, Next, in part three, we're going to talk about an even more complicated topic, which is what controls the probability that you'll end up getting infected by the virus. So please stay tuned for part three.
The Community Impact of COVID-19 Survey
In the past half a year, SCA Research conducted two surveys to assess the impact of COVID-19 on the global specialty coffee community. One key takeaway we saw in our open-ended questions was a strong focus on worker safety, customer safety, and sanitary practices in light of COVID-19. Respondents mentioned the implementation of safety and health procedures more than any other tool as a key competency during reopening. 80% of respondents mentioned new cleaning and sanitation procedures being implemented. This takeaway was the reason for creating the second video in the series with William D. Ristenpart.
The first video presenting the survey results
In the first video in the series, Community Impact of COVID-19: An Introduction, Katie von der Lieth and Peter Giuliano analyze what the SCA’s most recent survey tells us about the general impact of COVID-19, changes in sales channels, lost sales to date, future revenue expectations, and business decisions around remaining close or opening back up for service.
Special Thanks to Pacific Barista Series
This series is made possible with support from Pacific Barista Series.
