Indoor dancing is safe enough

by jefftkjefftk3 min read31st Oct 202120 comments

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Covid-19
Personal Blog

A few weeks ago, before organizing an outdoor contra dance I used microcovid to get an estimate of how risky it was, concluding that it is likely very safe. It's now too cold for outdoor dancing here in Boston, and I'm thinking about how risky indoor dancing would be, with masks and vaccination required. Breaking up the risk the same way as last time, but assuming a longer event and two lines:

[EDIT: this post originally had the scenario described as having a "talking volume" of "silent", but I've switched it to "normal" after discussion in the comments. While there isn't that much talking, the respiratory effect of moderate exercise is probably more similar to "talking" than "silence" or "shouting". I've updated the post below.]

  • ~16 from your partner. While your partner is not the only person your head gets close to, you're this close to at most one person at a time, so for simplicity assume its your current partner.
  • ~32 from your neighbors and next/previous neighbors.
  • ~48 from your next/previous hands fours, and the corresponding hands four in the other line.
  • ~24 from the hands fours one farther away, and the next/previous neighbors of the corresponding hands four in the other line.

This comes to ~120 microcovids, or ~60% of a cautious risk budget of 200 microcovids/week (1% risk of covid/year). It's about 5x safer than going to a restaurant. Outdoor dancing is still safer than indoor, but only by about 5x. [1] High-capacity air filters or high-turnover ventilation would help, if practical in the venue, lowering the risk to ~24 microcovids. [2]

Other considerations:

  • How risky is this event compared to what people are generally doing? Bars are open again, and have been for months, as is indoor dining. This sort of event is now fully legal here.

  • If we don't think it is currently ok but will be at some point, what would have to change? If the answer is that people who don't want to get vaccinated would have to get vaccinated, I don't think we should be waiting for them.

  • What is the current goal in limiting transmission? Essentially, everyone either needs to get vaccinated or get covid: there aren't really other options. So it seems to me that the main reasons to be cautious are making sure that we do not overwhelm the medical system, and allowing people who are at much higher than average risk to still meet their basic needs safely. For the latter group of people, it's not clear to me whether a slower or faster pace of infections is better: slower means more activities are possible, while faster means this ends sooner.

I now think it would be ok to resume indoor dancing, with masks and vaccination required. Am I missing anything? Other important considerations?


[1] This is actually a little surprising: in general microcovid models outdoor activity as 20x safer. What's happening here is that most of the risk for their model of the outdoor event came from the person you were currently interacting with 1:1, and they ignore ventilation in estimating how risky that is:

We are ignoring environment choice in this calculation. We are not confident that good ventilation or being outdoors substantially reduces the risk when people are this close to each other.

[2] In general, my experience has been that the numbers from microcovid are on the cautious side: they're well sourced, but if you plug in people's actual behavior and compare to actual infection rates, people seem to be getting infected less often than it would predict. Additionally, vaccinated people are less likely to be hospitalized, much less likely to die, and less likely to pass covid on to others.

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Checked through to the microCOVID models and found you marked everyone as being silent. Technically, sure, no one would really be shouting while they're dancing, but they'll be breathing heavily enough that exhaled droplets/aerosols/whatever would be similar. Choosing "loud" as the option increases everything by a factor of about 20.

After the discussion here and on FB, I've updated the post to switch from "silent" to "normal".

OK, did some digging. The relevant source is table 2 from Peng et. al., Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their Application to COVID-19 Outbreaks.

They calculate the following relative risk rates:
Silent: 0.0012 (1x silent rate)
Speaking: 0.0058 (4.98x silent rate)
Shouting / singing: 0.0350 (29.91x silent rate)
Heavy exercise: 0.0817 (69.83x silent rate)

IMHO, you could may argue for a risk factor of 1/10 compared to heavy exercise (which is 7x the silent rate), but my gut is that 1/5 (14x the silent rate) would be more likely, and something like 1/3 (23x the silent rate) would be a better and more conservative choice

This is a dance form with typical exertion somewhere between walking and lightly jogging. I don't think you get anything similar to shouting?

Yes, I emphatically agree with this (as does my consultant, who is an epidemiologist who works on COVID full time).

I think one can reasonably argue about the details: loud vocalizations create different aerosol patterns than exertion, and off the top of my head I'm not aware of any really solid data on how the two would compare. But I think your numbers are low by at least a factor of 5, and a factor of 25 seems very plausible to me.

Also: you've selected surgical masks when doing the µCoV calculation. Will that actually be true? If most people wear cloth, thin or loose (which seems most typical here), that'll increase the risk by another factor of 4.

On masks: I went with surgical based on my memory that at the outdoor event we held there was a mix of n95, surgical, and well fitting cloth masks. Ex: https://www.jefftk.com/davis-contra-2021-10-13.jpg

I think you're missing another big factor here: being within 3 feet of a single person for 2 hours is VERY different from being within 3 feet of a different single person, every 5 minutes, for 2 hours. I believe microCOVID actually maxes out the risk of catching COVID from a single person in less than that amount of time.

It is very different if you have high transmission probability per hour, but not if you have low.

For example, if I had a 50% chance of catching covid from a 15 minute interaction, conditional on the other person having covid, then if I spent 2 hours with that person, my risk still can't go above 100% times the chance that they have covid. On the other hand, if I spent that 2 hour period with eight sequential people, my risk can be up to eight times higher.

Right now, the tool estimates that if you spend an hour with a single person indoors who has covid, masked and vaccinated, the chance that you get covid is about 0.1%. This is low enough that the difference between one person continuously vs several seriously is not significant.

We've started doing contact improv indoors, masked, double-vaxxed in Toronto. Currently our base-rates are really low. The jam which is organized by Kathleen Rea is also rapid testing everyone before the start. I agree it's Safe Enough. My partner is still pretty covid anxious, party because we have a young child in our extended bubble who can't get jabbed yet, so I went to my first indoor jam wearing a p100 respirator. It... wasn't fantastic, but was doable. I definitely noticed my recovery after an energetic dance took much longer, this maybe partly bec I'm deconditioned from rehabbing patello-femeral pain, but also probably from the p100, but it's doable.

It was good to be jamming again.

If you can afford them, the rapid tests are a great idea: microCOVID doesn't model them, but I believe they cut your risk by about a factor of 4.

I don't think rapid tests are worth it here; see the follow-up.

For those who are bad at math words like I am and didn't click through to your link, I want to note that you mean, "they cut risk to 25 percent of the original risk", not "they reduce risk by 25 percent" :-) (I thought you meant the latter till I clicked through)

This isn't directly responsive to the question in the post (to which I agree activity approaching light jogging should probably be modeled as higher risk than silence, though I can't figure out how much).

But you may be interested in the following Facebook group, where Dorry Segev, a COVID researcher and organizer in the Baltimore dance scene, gives updates on best practices in holding dance events to manage risk levels https://www.facebook.com/groups/158671312715141/?ref=share

(It may be worth asking your question there as well!)

I've updated the post to switch from "silent" to "normal"

This isn't directly responsive to the question in the post (to which I agree activity approaching light jogging should probably be modeled as higher risk than silence, though I can't figure out how much).

Using microcovids, I evaluate any dancing related scenario as "talking volume: loud", which they assign a x5 risk increase to.

Can you elaborate on why you see "loud" as the appropriate level? That makes a significant difference in terms of risk level.

I dance contact improv, which is a very flexible, open framework. I've had very interesting and wonderful CI dances where (likely) no one involved had an elevated heart rate. I've also had CI dances where I spend the entire time (5 - 10 minutes?) up in the cardio burn zone. I can't know ahead of time what I'll be doing, and sometime akin to an aerobics class seems better to eval as "loud talking", in terms of volume of air being exhaled.

I wonder if your views on this have shifted at all since

  1. Cases have started rising again, even in the northeast

  2. Very promising antivirals on the horizon.

Zvi makes some excellent points in his last piece, which make me more inclined to tough it out.

Also, based on some of the other comments here, and my own intuition, I wonder how you feel about the more naive heuristic that after an evening of contra dancing, everyone who's infected with a given respiratory virus will have passed it on to everyone who's susceptible?

Here's the risk calculator I tend to gravitate towards. It attempts to answer the question "What should be the capacity of a given room over a certain period of time?"

https://indoor-covid-safety.herokuapp.com/apps/advanced

Essentially, everyone either needs to get vaccinated or get covid: there aren't really other options.

I disagree, there is at least one other option, the one you are trying to avoid: get vaccinated AND get covid.

Sorry, what I was trying to say is that there aren't any other options for unvaccinated people who have not yet had covid.