Dancing With the Virus

In a recent email to an old friend I described my movements through the world of social distancing:

I continue to go out twice a day for runs and walks. It’s started to feel more like a kind of game, keeping track of who else is out there and altering my trajectory to maintain safe distance. Bicycles coming up from behind are the biggest challenge, so I’ve adjusted my habits to looking behind me every 30 seconds or so. I’ve also taken to wearing my Biohazard t-shirt on afternoon runs — it might not serve as fair warning but it seems to cloak me in a kind of absurdist protective psychological bubble. The first day I wore it a passing motorist rolled down his window and shouted NICE SHIRT at me — that’s the spirit.

In reply my friend linked me to a NYT article written by a dancer, who describes the collective maneuvers required to sustain social distancing in public places as a kind of choreography:

In this time of confinement, we have been given one immeasurable gift — the freedom to go outside. In exchange, we must abide by a simple rule: Stay six feet away from others. As choreographic intentions go, that’s not remotely vague. Yet during my runs and walks in Brooklyn over the past few days, I’ve noticed that six feet doesn’t mean the same thing to everybody.

Spatial awareness, like coordination, isn’t a given. Watching the choices people make when they move in public, much less in this time of social distancing, can be shocking, from the much-bemoaned tourist who comes to a grinding halt in Times Square to the woman with a yoga mat knocking people aside to get her spot on the floor. (It’s OK; she’ll still feel good about bowing her head and saying namaste.)

The six-feet-away rule is simple, but it’s a proxy. We’re not trying to dance around one another; we’re trying to dance around the virus — an invisible partner.

A 2007 study measured the distances that breath droplets can travel before evaporating when expelled by breathing, sneezing, and coughing. Ordinary breath travels at a rate of 1 meter per second, with droplets evaporating within less than 1 meter distance from the breather. Coughing doubles the droplet spray distance, so maintaining a social isolation zone of 2 meters (612 feet) seems adequate for coronavirus.

But what if the breather is walking? At 3 MPH, a walker travels 1.3 meters per second. Add walking speed to breath speed and the walker’s breath droplet precipitation zone extends to 2 meters — still good, as long as nobody coughs or sneezes. What if another walker is walking toward me? Add that person’s 2 meters to mine = 4 meter distancing seems okay. What about a runner? At an average running speed of 6MPH or 2.7 meters/second, the droplet trail extends to around 3.5 meters. A bicyclist traveling at 15MPH generates a breathing droplet trail of around 7.5 meters.

These calcs support the intuitive sense that safe distance is correlated with speed — pretty much like anticipating safe braking distance while driving at different speeds. It’s the game played at level 2, demanding more intricate choreography than the simple 6-foot rule of level 1.

On the trails it’s the bicyclists who make the choreography most difficult, dragging their spray of breath droplets in their wake while coming up at speed from behind. But the walkers tend to stretch themselves in clumps across the entire width of the trail. So I’ve taken to walking and running along the sides of the roads. Drivers of cars are pretty much keeping their breath to themselves. And while cars too exhale noxious fumes, these days it’s a matter of picking your poison. And of course being bumped by a fellow pedestrian isn’t quite the same level of hazard as being bumped by a car.

It’s 7am — time to dance my way through the viral chorus line…

15 thoughts on “Dancing With the Virus

  1. If you were on a train going south at 26 mph and the sun rises at 6:50 am when 3 crows flew to the northeast, how far would two spittle droplets travel when pah-too-ee-ed by a bicyclist pedaling 60 cycles per minute?

    Liked by 1 person

  2. “Systems thinking leads to another conclusion, however, waiting, shining, obvious, as soon as we stop being blinded by the illusion of control. It says that there is plenty to do, of a different sort of “doing.” The future can’t be predicted, but it can be envisioned and brought lovingly into being. Systems can’t be controlled, but they can be designed and redesigned. We can’t surge forward with certainty into a world of no surprises, but we can expect surprises and learn from them and even profit from them. We can’t impose our will on a system. We can listen to what the system tells us, and discover how its properties and our values can work together to bring forth something much better than could ever be produced by our will alone. We can’t control systems or figure them out. But we can dance with them!” Donella Meadows, Thinking in Systems

    Liked by 1 person

  3. I thought she nailed why revolutions fail, but we try anyway. Morin has a great line about how modern thought is all a kind of Pascalian wager. Our local farm stand is selling fresh asparagus. It’s really good. They’re not wearing masks.


  4. Will it be poison put in my glass?
    Or will it be slow or will it be fast?
    The bite of a snake, the sting of a spider
    A drink of Belladonna on a Toussaint night
    Hiding in a corner in New York City
    Looking down a .44 in West Virginia


    1. Good one.

      “On the basis of these results the scientist advises that for walking the distance of people moving in the same direction in 1 line should be at least 4–5 meter, for running and slow biking it should be 10 meters and for hard biking at least 20 meters.”

      Those are even bigger safety bubbles than my calcs came up with.


  5. Hey Carl, good to see your unmasked virtual self. I was going to write a post about masks but didn’t get around to it. Here’s a link to a 2015 study if you or your vegetables are interested. SPOILER ALERT: Cloth masks offer some protection if people who are already infected wear them. But if you’re not already infected, a cloth mask is worse than no mask at all. Anne tells me that y’all have set up your egg stand as a kind of self-serve during present self-quarantine conditions — good idea.

    Have you kept up with Andy Clark since he achieved notoriety as godfather of extended mind theory? He contends that the main function of consciousness is to predict the future, in order to enable intentional adaptations that enhance the survive and thrive instincts. Based on last night’s rain I’m guessing that the antelope are likely to show up at the watering hole, so let’s take a hunting party down there after lunch. I’d say that multiple alternate possible futures are arrayed out there, with probability estimates attached to the likelihood of their eventually becoming part of the present actual reality. Pascalian indeed. Interventions can be designed to boost the likelihood of one desirable alternate future taking shape or to dampen the odds of more dangerous possible futures. Experiment, evaluate, modify, iterate, chachacha. It’s kind of a dance, or a game, or guerrilla warfare…


  6. I’d be far more inclined to shop at an outdoor food stand than in a grocery store. Here’s the basis for another post I could have written, excerpted from an email I sent on 19 March:

    This morning I went to the grocery store — mostly full shelves but no TP, Kleenex, cleaning solutions. Henceforth we’ll have the store select our stuff for us and we’ll either pick it up at the loading dock or have it delivered. My math:

    – 100 documented cases in NC, but epidemiologists estimate that there are probably 10 times that many including the unconfirmed and the presymptomatic. So make it 1000 cases in NC.
    – Population of NC = 10 million, so 1000 cases = 0.01% of the population.
    – Assume that this morning I come in contact with 100 people at the grocery store; rough odds that at least one of them has the virus = 1%. I’ll take that risk.
    – Given the current rate of infection, by a week from now there’ll be 10 times as many cases in state = 10,000 = 0.1% of the population. If I come in contact with 100 people at the grocery, the odds that at least 1 of them has the virus = 10%. That seems too risky for me.
    – By two weeks from now, 1% of the state population will be infected, and the odds of at least 1 out of 100 people I encounter in the store having the disease will be about 70%. No way.


  7. There seems to be a lot of wiggle in how to calculate odds and even how to define the game. Here’s a doctor’s response to the droplet dispersion study:

    “1) Critiquing the “Belgian-Dutch Study: Why in times of COVID-19 you should not walk/run/bike close to each other” (what’s the infectious dose for COVID anyway, and why 6′ is necessary, but 30 is overkill); 2) How that idea of infectious dose dictates how we can interact with the world/food/people/mail/things other people have touched.

    There was an ominous-sounding blog post stating that any form of outdoor exercise where you pass within 30 feet of another person will lead to transmission of COVID-19. It was written by Jurgen Thoelen, a Belgian expat in Russia who works in cloud computing, and who also founded a sports training agency. He got the information from an interview given to a Brussels newspaper by Bert Blocken, an engineering researcher interested in wind tunnels and the aerodynamics of sports (involving concepts like athletes drafting off each other).

    Bert Blocken, wind tunnel sports guy, decided to get into experimental virology and then decided his conclusions were too important to submit for publication or any form of peer review, so immediately posted them on twitter and contacted a newspaper for an interview. [Since the Medium piece, he has submitted a pre-print]. He did not consult a virologist, clinical physician, or epidemiologist in his research. Since we’re all used to only having vetted, peer-reviewed research put out in the public square like this, readers- including Thoelen- took it as scientific fact.

    Even though Thoelen didn’t have it available to him, let’s look at the Blocken pre-print (non-peer-reviewed) paper. He made a wind tunnel and installed some spray nozzles, with the holes in the nozzles set to sizes which somewhat line up with human droplet and droplet nuclei particles. He set different temperatures, and different levels of humidity, and different windspeeds. He decided that whether or not the particles evaporated was a good proxy for whether or not they’re infectious. And he simulated runners and cyclists side-by-side / behind each other /diagonally, and calculated how many non-evaporated droplets hit them. He concluded if ANY droplets hit the trailing athlete, they’d get infected; and came up with the 30-feet rule, implying all of the guidance on social distancing was laughably ineffective.

    Several immediate problems are obvious:
    – Humans aren’t spray nozzles generating a continuous mist of droplets under steady pressure
    – Droplets are infectious if they contain live virus, and denaturation occurs prior to complete evaporation. A LOT OF PARTICLES ARE DEFECTIVE IN HUMAN RESPIRATORY VIRUSES- the particles “fail to infect” (this in virology is called the particle-to-PFU ratio, and the coronaviruses make a bunch of useless ones).
    – No attempt to use SARS-CoV-2-specific infectious particle size was made
    – Unless you’re heading straight into a gale, particles from a cough/sneeze spread out in front of you and disperse laterally
    – MOST IMPORTANTLY BY FAR: there was no attempt made to simulate an appropriate infectious dose. How many virions do we need to inhale in order to reliably become infected? How much virus does an infected person generate, anyway?

    The answer is: we don’t exactly know (unless you want to volunteer for a controlled experiment snorting different concentrations of virus up your nose and waiting to see when you become infected, we might have to rely on mice). But we DO know, definitely, it’s more than 1, AND:
    -We know asymptomatic people have very high concentrations of virus in their respiratory tree and nasopharynx, on the order of 700 million viruses per 1000 cells– BUT they aren’t successful at getting all that virus out in the world.
    – At 8 inches away infected people generate only about 6000 copies/ mL (from that facemask study yesterday).
    – The infectious dose of the MERS coronavirus is between 1000-10,000 virions, to produce symptoms. Estimates are SARS-CoV-2 will be in the high 100s/low1000s.

    SO: At 8 inches, you’ll get 2-3x the infectious dose, with a dispersion effect showing very rapid trail off-after that. 6 feet = 72 inches = 9 separate iterations of “trail-off,” taking our 8 inches-from-the-face Petri dish as a standard unit. That’s a lot. We also know most everyone out exercising has an innate immune system, too. So run like the wind, everyone, Inhale some virus, you can still beat it.

    Summary: if you’re closer than 6′, you’r have a good chance of getting an infectious dose of virus. Farther than than, you don’t. But of course, risk is never actually 0… it’s just very improbable.

    And much, much, much more importantly- we know there is a HUGE difference between “viral RNA detected” on a surface and at a distance, and actual live infectious virus. Bringing us to:

    2) It’s really *almost* impossible to get COVID from a cereal box or a piece of mail.

    Several good, high-quality, peer-reviewed studies have demonstrated that detectable viral RNA is found on various inert surfaces days after virus was first placed there. That cruise ship showed viral RNA weeks after the last people disembarked. That’s naturally sparked worries about eating virus (on food), and handling objects which might have been handled by infected people.

    Firstly- viruses denature (degrade/fall apart) rapidly in the environment. They need cells to “live” (replicate) and without cells, they’re at the mercy of entropy. Their protein coat dissolves and denatures, and eventually, their core RNA is left lying around, like bleached bones in the sun. Although the world is awash with enzymes which digest RNA some sequences will survive to be picked up by an enterprising researcher with PCR. And without that spike protein to dock with a living human cell (via that ACE-2 receptor), SARS-CoV-2 RNA can’t do anything. It can’t infect a cell and begin replicating. So when experiments based on PCR (which amplifies just the RNA) say they detect viral RNA, they are not necessarily detecting infectious virus. Over very long periods of time- the cruise ship- they almost certainly are not.

    And when they say “any infectious virus”– they mean ANY. Remember the discussion about infectious dose above? On cardboard, in the NEJM paper where they computer-simulated infectious virus by spraying aerosols on surface and modeling the decay (NOT confirmed by PCR), the virus fell below the infectious dose within a couple of hours- even assuming it was 100% viable in each and every particle, which it totally isn’t.

    Secondly, it’s a respiratory virus. It can only dock with certain cells in your body. When you eat live, infectious virus, the enzymes in your saliva start to work- and then, within a few seconds, the virus hits your stomach where the acid environment causes it to fall apart. Although virus has been isolated from stool, good-quality data shows that it was not infective virus, it was mostly denatured and digested virus.

    So, the cereal box. Let’s say someone spray-sneezes all over your cereal box. The virus has a half-life of 70 minutes, on cardboard, so you’d have to pick it up right away and rush home with it. A small amount of infectious virus is transferred to your hands when you pull it off the shelf (you need a few hundred/thousand to successfully end up in some part of your body with the correct receptors , remember?). The virus cannot burrow into your skin- so, on your hands some will denature further, just hanging out; some will fall off whenever you touch anything else. By the time you accidentally touch your face or wipe your nose, you don’t have much left. And then- it’s just on your face, close to a mucus membrane, maybe some gets in? Unless you take a deep, fragrant, admiring sniff of your hands, or the cereal box… it’s tough.

    Bottom line: washing your hands and not touching your face is good. Keep doing that. And if you like bleaching and wearing gloves for the sense of absolute harm reduction and a feeling that you’re controlling at least something in this crazy world, by all means continue to do so But- if you have to choose between a mask and the bleach/gloves routine: PLEASE CHOOSE THE MASK. THE MASK IS SIGNIFICANTLY MORE LIKELY TO EFFECTIVELY PREVENT TRANSMISSION.”

    Liked by 1 person

  8. Thanks Carl. I”ll stick with my own, less restrictive social distancing metric: 7.5 meters from a bicycle, not 20 meters. Even in non-plague conditions I wish that cyclists coming up from behind would issue the “on your left” warning 7.5 meters before passing me. That’s about one second of warning time — enough to hear, to process, and to react by stepping aside, avoiding either the toxic exhalations or the actual physical bicycle+rider. In my experience most bicyclists announce themselves at about the point where they’re zooming past me — not very helpful.

    Also, as this MD’s reply rightly observes, people aren’t spray nozzles: the farther away from the breather’s nose/mouth, the lower the concentration of breath droplets. So even if I get caught momentarily in a bicyclist’s slipstream, the proportion of virus-infected air I inhale would be a lot less than if I were riding along next to the cyclist. The bottom-line advice — PLEASE CHOOSE THE MASK — ought to be issued with qualifications, per the study (peer-reviewed, published) that I cited earlier in this thread: PLEASE CHOOSE THE SURGICAL MASK. If you’re not already infected, the cloth mask is worse than no mask at all.


  9. Here’s another article on aerosol distribution. Published by the CDC,this one from samples collected in COVID wards in Wuhan hospital wards.

    This study led to 3 conclusions. First, SARS-CoV-2 was widely distributed in the air and on object surfaces in both the ICU and GW [general COVID ward], implying a potentially high infection risk for medical staff and other close contacts. Second, the environmental contamination was greater in the ICU than in the GW; thus, stricter protective measures should be taken by medical staff working in the ICU. Third, the SARS-CoV-2 aerosol distribution characteristics in the GW indicate that the transmission distance of SARS-CoV-2 might be 4 m.

    As of March 30, no staff members at Huoshenshan Hospital had been infected with SARS-CoV-2, indicating that appropriate precautions could effectively prevent infection. In addition, our findings suggest that home isolation of persons with suspected COVID-19 might not be a good control strategy. Family members usually do not have personal protective equipment and lack professional training, which easily leads to familial cluster infections.

    So: keep your distance, wear a surgical mask, wash your hands.


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