Post #811: Qualitative rankings of activities by risk of COVID-19 infection

Posted on September 12, 2020


One remarkable aspect of this epidemic is that you can’t get any good information on what actions are risky, or not, for catching COVID-19.  How much does, say, going to the gym regularly raise your risk of COVID-19 infection, if at all? In other words, what are the odds that a trip to the gym will get you infected?

That question — what are the odds — turns out to be remarkably difficult to answer.  I laid that out fairly well in Post #716.  In a nutshell, even if they could accurately identify the  activity that got an individual infected, typically, nobody has the data on how many individuals engage in that activity.  You might know that (e.g.) 20 people in Virginia were infected in the course of routine dental care, but you don’t know if that’s 20 times in 20,000 visits, or 20 times in 2,000,000 visits.

For now, the bottom line takeaway from Post #716 is that you aren’t going to see any good, systematic information on your odds of being infected by doing X.  All you are going to see is more-or-less what anybody can cobble together.  Targets of opportunity.  And whatever has been analyzed in the scholarly literature.

Keep that in mind when you see studies that seem to be talking about the risk of catching COVID-19, from various activities.  What you are going to see published is probably better than nothing. And probably, no matter how it gets written up, almost none of it is actually going to tell you the odds of infection associated with any particular activity.

With that as background, yesterday the US CDC announced the results of one small-scale, sample-of-convenience study of individuals who had COVID-19 symptoms About half actually had COVID-19, the other half did not.  They contrasted those two halves in terms of what activities they had done in the prior two weeks.  Click here to see the study.  Or read a plain-language writeup of the results in the Miami Herald.

The CDC’s bottom line is that restaurant dining of any sort — indoor or outdoor — was about twice as common among those who had COVID-19, compared to those who didn’t.  And they found a weaker result for going to bars/coffee shops does as well.

The implication is that restaurant dining (and bar/coffee shop use) raises your risk of infection.  And that seems plausible enough.  But you still have no clue what the odds are.  Does it raise your risk from infinitesimally small to merely incredibly small?  Or is restaurant dining in the COVID-19 era the equivalent of drunk driving?

So I decided to compile what I could find, about who says what is risky, and why.  It ain’t much, but it’s all we’ve got.  This is the first of two postings, comparing various lists of what’s risky and not.  Detail follows.

Qualitative rankings of activities based on professional judgement.

It’s not as if we lack for advice about risky behaviors.  What we seem to lack is anything in the way of hard data.

So let me start off by compiling various lists that I’ve found.  These are all qualitative rankings They suggest that some activities are riskier than others.  But there’s no hard data behind the lists, and there’s no quantitative estimate of the odds of getting infected from any one activity.

You have to be cautious about an echo chamber effect in an analysis like this.  This is based on professional judgment.  Which is probably strongly influenced by reading other summaries of professional judgment.  So this may not reflect N independent judgments of risk.  It might just reflect a lot of group-think.  There’s no way to tell.

Let me sum up what I see as some commonalities.

  • Everybody hates bars.  I’ve noted that before.
  • Nobody seems to think that fomite transmission (infection via droplets on inanimate objects) carries a huge risk.  E.g., nobody considers eating take-out or opening the mail to be risky.  But people do vary in their assessment of the risk you take in touching “high touch” surfaces, touched by many individuals.
  • Most people rate outdoor activity as less risky, but:
  • Differences in risk rankings for outdoor activities are often based on how crowded the ranker thinks the outdoor scene will be. So differences in these lists often amount to “fill-in-the-blank is great, but a crowded fill-in-the-blank is not”.

By the time I got through with all of these, I think that most of these lists embody little more information than you can get from this simple chart from the Japanese Ministry of Health.  The more you find yourself in close, crowded conditions, the riskier the situation.  At the end of the day, I’m  not sure there’s any more content here than that.  And wash your hands.

0: The CDC’s advice on daily activities.

The CDC has a page giving advice on how to go about normal everyday activities.  It doesn’t offer assessment of risk, and the advice is pretty mundane.  (It is also out-of-date, given the CDC’s statement that transmission of COVID-19 via inanimate objects is extremely rare.)  It can be boiled down to a handful of (what by now should be) commonsense items.

  • Transact business by phone or internet if possible.
  • Go when it’s not crowded
  • Don’t shake hands
  • Exercise outdoors if possible
  • Wear a mask
  • Wash your hands.
  • And so on and so on.

1  State re-opening plans.

Every state re-opening plan is, in effect, a ranking of behavior from (what somebody believes) is least to most risky.  Initial steps in re-opening start with the things that were thought to be least risky.

I reviewed the commonalities of those plans in Post #684 Summarizing, from lowest to highest risk.

  • Distanced outdoor activity (reopening of parks, beaches)
  • Outdoor dining
  • Indoor dining
  • Large gatherings
  • Bars

The treatment of church services is muddled by legal questions, so the fact that attendance at church isn’t on the list is not clear.  And as a matter of course, these lists don’t mention “essential business” activities such as grocery shopping, that had to stay open in any case.  They only lists activities that could have been restricted.

Most state reopenings are explicitly modeled on Federal guidance, so that is a classic case of an explicit echo chamber.  They mostly look alike because they mostly align with a single Federal template.

2 Texas Medical Association

You can see a similar but more detailed listing from the Texas Medical Association, the principal physician professional association in Texas.  This chart is primarily based on the opinions of their physician members.  (The chart is at this link (.pdf)).  They rank them, from lowest to highest risk:

  • Opening the mail
  • Getting restaurant takeout
  • Pumping gasoline
  • Playing tennis
  • Going camping
  • Grocery shopping
  • Going for a walk, run, or bike ride with others
  • Playing golf
  • Staying at a hotel for two nights
  • Sitting in a doctor’s waiting room
  • Going to a library or museum
  • Eating in a restaurant (outside)
  • Walking in a busy downtown
  • Spending an hour at a playground
  • Having dinner at someone else’s house
  • Attending a backyard barbecue
  • Going to a beach
  • Shopping at a mall
  • Sending kids to school, camp, or day care
  • Working a week in an office building
  • Swimming in a public pool
  • Visiting an elderly relative or friend in their home
  • Going to a hair salon or barbershop
  • Eating in a restaurant (inside)
  • Attending a wedding or funeral
  • Traveling by plane
  • Playing basketball
  • Playing football
  • Hugging or shaking hands when greeting a friend
  • Eating at a buffet
  • Working out at a gym
  • Going to an amusement park
  • Going to a movie theater
  • Attending a large music concert
  • Going to a sports stadium
  • Attending a religious service with 500-plus worshipers
  • Going to a bar

3:  Health Line Health News

Here’s a list from health news reporting agency that is more-a-less a compilation of what anyone in a position of authority has flagged as risky.

Unlike this lists above, this is a list of places considered high-risk, that I have tried to sort from lowest to highest risk.  So it should read like the bottom half of the rest of the lists.  There are no low-risk activities in this list.

  • Hair and nail salons
  • Crowded workplaces
  • Large outdoor gatherings
  • Public transportation (plane, bus, train, subway)
  • Community pools and beaches, if crowded
  • Concert halls, churches, theaters
  • Bars

4:  Washington University infectious disease expert Dr. Andrew Janowski.

These lists are based on the professional judgment of Andrew Janowski, M.D., an infectious disease expert at Washington University in St. Louis. You can read the news writeup of it at this link.  Unlike all the other lists, Dr. Janowski does not rank going to a bar as the riskiest situation.  Instead, he reserves that honor for events with large crowds and no masks, such as movies, concerts, church services, and sporting events.

Here, I have copied in the graphics from the website of KSDK, a St. Louis TV station.

If most or all area wearing masks and social distancing.

Source: KSDK, link cited above.

If few or none area wearing masks or social distancing.

Source: KDSK, link cited above.

5:  Infectious disease expert Dr. Sandra Kesh.

These are again based on professional judgment.  You can read the full writeup on CNET.  Uniquely, Dr. Kesh ranks flying as riskier than drinking in a bar.  You can see her reasoning in the writeup.

This list is from least to most risky activities:

  • Going to a park.
  • Seeing friends outside
  • Eating outside
  • Grocery shopping
  • Going to a gym
  • Seeing friends inside
  • Eating inside a restaurant
  • Getting a haircut
  • Going to a bar
  • Flying / air travel.

6:  Mayo Clinic list of outdoor activities

This is a list of outdoor activities only, from least to most risky, developed by the  Mayo Clinic.  This assumes mask use and social distancing.

Low risk:

  • Walking, running and hiking
  • Rollerblading and biking
  • Fishing and hunting
  • Golfing
  • Kayaking, boating and sailing
  • Fitness classes, held outside, that allow distance
  • Picnics.
  • Farmers markets.
  • Gathering with friends
  • Drive-in moviesModerate risk:
  • Restaurant patio dining.
  • Camping with the people you live with.
  • Swimming pools and beaches
  • BBQs and outdoor potlucks
  • Sports and sporting events

Higher risk:

  • Large gatherings.
  • Summer camp activities.
  • Playgrounds.

    Summary so far.

I think I’ve reached the point of diminishing marginal returns on this exercise.  I might put in a few more lists as I find them.  But I think that that two factors largely explain differences across lists. 

One is how crowded the list-maker expects the situation to be.  Mayo, above, lists outdoor sports as relatively safe because they assume that everyone will be property socially distanced.  Others lists sporting events as unsafe because they assume that proper social distance won’t be maintained.

The other is the perception of risk of fomite transmission (infection by touching virus-covered inanimate objects).  Above, Mayo rates playgrounds as risky due to the presence of surfaces touched by many hands.  Others rate them as safer, due to the presumed social distancing in an outdoor setting.

All-in-all, its tough to say that there’s any insight here that goes any deeper than that Japanese Health Ministry poster, or the plain-Jane advice from the CDC.  Avoid crowds.  Wear a mask.  Avoid contact.  Do your activities outside if possible.  I think that much of the rest is just based on varying opinions on how much those rules are broken in any particular situation.

The next post will summarize a few situations where there actually is some quantitative estimate of “the odds” of infection, in a given situation.