May 17th, 2020

Does Strictly Limiting Outdoor Activities Help Prevent the Spread of COVID-19? A Call for Reason

I really miss playing tennis.

Tossing that out there to confess up front why the following might not be the world’s most objective perspective.

But take a look at this:

Jeepers, much of that advice strikes me as silly. Or, as put bluntly by one respondent here:

So, if I understand well, I can sleep with my wife but playing tennis with her just crosses the line, right? S**t, this is a tricky virus!

Ok, back to me and tennis. Some years ago, my wife gave me a nice tennis racquet for a certain milestone birthday.

She had just watch me play in a casual pick-up tournament for novice players at a local park, and noticed I couldn’t shut up about how fun it was for weeks.

It was easily one of the best birthday presents in the history of the planet. I’ve been playing tennis 2-3 times a week ever since. While walking, biking, or driving to the courts, I get this delightful giddy feeling of excitement each time.

Plus — and other devoted amateur athletes and hobbyists will certainly recognize this feeling — playing tennis is one of the few activities during which my mind goes blank on work issues. Patient care worries, manuscript deadlines, demands for learning objectives, human resources struggles, required online learning modules, email overload — all gone.

Boy, I miss that.


So I acknowledge some bias here on the question of whether strictly limiting outdoor activities actually limits the spread of COVID-19.

And — must be said — missing tennis is trivial compared to the hardships, health issues, and losses wreaked by this awful virus.

But follow me on the tennis thing anyway, because I do think that some of our most important public health messages get diluted by nonsensical and absolutist guidelines not rooted in science.

Where do we see most of the spread of COVID-19?

Households, especially those that can’t isolate symptomatic individuals due to lack of space. Crowded settings with poor ventilation. Nursing homes. Shelters. Ships. Call centers. Restaurants and bars. Parties. Family gatherings. Public transportation. Meat packing plants.

What do all of these settings have in common? They’re indoors. Or they’re crowded. Or even worse — both.

That’s because the likelihood of getting infected directly correlates with the amount of virus in the air we’re breathing, and the time we spend breathing it. Read this magnificent and widely circulated post by Dr. Erin Bromage, if you want more details.

Or this wonderful summary of carefully done transmission studies by Dr. Muge Cevik:

Outbreaks linked to outdoor activities invariably involve crowds — this Italian soccer match, for example.

How about the infamous Spring Break 2020 revelers, basking outdoors in that glorious sunshine while the rest of the country watched, horrified?

It’s possible that they contracted COVID-19 on the beaches, but much more likely these transmissions occurred during the evening hours while packed together like sardines — not just in their shared hotel rooms, but also while attending museums, poetry readings, and chamber music performances.

(Oops, I mean bars, bars, and more bars.)

Again, the problem with too-strict or illogical public health advice is that they make us distrust all the messages. As noted by population scientist Dr. Julia Marcus in this excellent and thoughtful piece:

The choice between staying home indefinitely and returning to business as usual now is a false one. Risk is not binary. And an all-or-nothing approach to disease prevention can have unintended consequences.

Some take-home messages? Yes, avoid crowds. And indoor spaces with poor ventilation. Keep your distance from others when you can — and when you can’t, limit the time spent in close proximity. And wash your hands a lot.

But do go outside and get some fresh air. Don’t yell at the jogger across the street without a mask, or the person having a picnic in the park with their family — they are not going to infect you.

And let’s be reasonable when it comes to public health messages, focusing on what really counts.

Tennis anyone?

What’s the most important public health message on this sign? (Hint: It’s not “Please do not touch or sit on benches.”)

22 Responses to “Does Strictly Limiting Outdoor Activities Help Prevent the Spread of COVID-19? A Call for Reason”

  1. Howard Grossman says:

    YES, YES, YES Paul. Thank you, as always, for injecting sanity into this insane world. People are so overwhelmed with the deluge of speculation, recommendations and disinformation about Covid-19 that they are literally turning off (the TV, the radio, their brains). A friend calls what’s on TV and in the newspapers “terror porn.” All designed to keep eyeballs focused on that medium. Countries that focused on simple HIV prevention messages such as wear a condom for intercourse and don’t share needles did much better than the US where people worried about every unlikely cause of transmission and so confused everything. I think your messages are perfect. Avoid crowds and don’t have big parties, and when you do go into an enclosed place like a market, wear a mask. Sanitize hands going in and out of places (“foam in/foam out’), wash your hands when you come in from outside. If you are sneezing or coughing or sick in any way STAY HOME (which of course entails getting employers to change outmoded HR policies). I think with these simple things that are not overly burdensome for most people, we can put a huge dent in transmission. So grateful always for your calm insight.

  2. Mark Romeo says:

    As a NYC resident, I appreciate these sane words in a time of such hysteria and mis-information. Thanks Paul!

  3. Max says:

    Well said – of course people should soothe themselves with non-extreme measures. Only a “small number” will die anyway – and you can play tennis.. Better than being indoors for ever (although you might be in an urn forever). Of course Corona virus might live on many surfaces for extended periods of time, but perfect hand sanization is always available (you’ll reach into your pocket with your contaminated hand to get the hand sanitizer – right – and possibly even share that with someone else, because you’re a nice guy). Thanks for offering this sanity – but I think I’ll stick with my sanity, if you don’t mind.

  4. Loretta S says:

    Read Dr. Bromage’s post last week and immediately decided it needs to be read by my nursing students taking microbiology in the fall. It so perfectly explains what is risky and what is not-so-risky when it comes to viral transmission. (I won’t be singing in a choir any time soon.)

  5. Carl G Weber says:

    Agree with all of above. Why do those claiming we need to ban these outdoor activities say it’s based on science. At best it’s expert opinion and for that we know where is lays on the hierarchy of medical evidence….at the bottom! Wish we had more experts such as you countering them!
    PS: if something like this was posted on FB it would likely be banned. Not joking.

  6. Libby Ernharth says:

    And swimming?? Chlorinated pools where youth and masters teams practice… tell me how this isn’t a reasonable option outside. I am worried for my own sanity (I confess, I love my masters team, the Flying Fish Heads) and my swimming colleagues in W. PA. Let the outdoor pools be used for workouts to start. Thank you for sanity.

  7. Kristi Henzel says:

    It seems to me that what is needed here is a study of duration of viral viability on tennis balls…and lilacs, frisbees, footballs, baseballs, basketballs and soccer balls!

  8. Babak says:

    What’s the most important public health message on this sign? Wash hands frequently.

  9. Luciana says:

    Bom dia Dr Paul Sax e colegas médicos, escrevo em portugues porque sou Brasileira e tenho orgulho do meu idioma. Gostaria de destacar que sou uma admiradora da sua carreira, especialmente em relação aos seus trabalhos em HIV. Contudo, seu texto me chamou a atenção pelo individualismo das ideias. Ja pensou que se todas as pessoas saissem para jogar tenis as quadras ficariam lotadas? O seu direito de sair de casa é maior que o das outras pessoas? É claro que se voce tem uma quadra de tenis na sua casa e quer jogar com sua esposa voce deve jogar (tenho certeza que ninguem aqui vai acreditar que nao poderia, correto?). Gostaria tambem que informasse as fontes nas quais podemos entender que o virus se propaga pelo ar e nao por superficies. Obrigada, se cuidem e fiquem em casa se puderem


    keep your eye on the ball. But what about your hands? Wear gloves? sanitize often and drop your ball/Into a vat of alcohol! sense or nonsense. Mostly agree –is the devil still in the details?

  11. brian Mac says:

    agree !!

    One other important note.. We keep talking distancing, and washing hands but why don’t we tell everyone the following

    You have to assume that EVERYTHING you touch has the virus on it, Put that in your mind set, and preach it Nationally !!!

    Then you know you can’t touch your face without washing first SIMPLE

    the people I know got the virus by not getting anywhere near the infected person but touched something the person touched

  12. manuel cervantes says:

    thanks Dr Sax… Sanity & Common Sense in times of paranoia. The SARS-CoV-2 pandemia is a real threat. The magic remedies are not. Lack of evidence of some recommendations, real danger of many of them (wear gloves in all day basis) and contradictions as the number of people sharing tennis court or swimming pool. We need you !!!

  13. Raymond Reiser says:

    It looks like someone likely manipulated the sign. Happens out here too. All of the expected “yes” responses have what appears to be a sticker stating “no” taped over them. You have to zoom to see. I suppose it’s preferable to the threats towards park workers i saw scrawled on the sign closing my local bark park.

  14. Yoshihiro Ishida says:

    Thank you for a great article. In Japan, many runners are obliged to wear masks in order to avoid being harassed by others. I hope your words get around and help Japan regain sanity.

  15. Fernando says:

    Great, I have Been walking on the beach Éveryday with my dog since Covid spreads in Brazil. Keep distance from each other. Do not go to overcrowd locals. Stay at home with your family and work with many cautions. Life cannot stop and it seems The virus Will be our “friend” for a long time.

  16. Sue Swindells says:

    So I miss playing tennis as well. Just talked to some friends in Colorado (married couple) and they have resumed playing doubles with this plan. Each pair take their own tennis balls with their initials on them, They only touch their own balls, and when needed, return the other team’s using a racket or well-aimed kick. No hugging or handshakes, but everyone has a good time.

    This sounds like a reasonable plan to me; am thinking of doing the same thing myself.

  17. Ruth C Lindo says:

    Outdoor spaces in warm weather are of course the least likely place for transmission of COVID 19 to occur. In part this is due to air currents which disperse clouds of microdroplets containing viral particles, in part this is due to the dilutional effects of the atmosphere decreasing viral load, and in part due to UVC light and heat. Having said that the major flaw is human behavior. There is no scientific evidence to back up the 6 foot rule, and what evidence we do have suggests that greater distances, perhaps twice as far are necessary. There is also the problem of compliance with masks. So I would say that outdoor spaces are the ideal place to avoid COVID 19, if and only if people engage in adequate social distancing, which I would define as 12 feet rather than 6.

  18. Jon Blum says:

    This has been a topic of intense debate in my cycling club. The effect of breezes and dilution makes the great outdoors safer (unless you sit on a bench or sniff one of those deadly lilacs!). However, every cyclist who rides in groups has been hit at some point by a snot-cloud when somebody sneezes or blows ahead of them. So most of us are trying to ride alone, or maintain substantial separation and stay out of each others’ slipstreams (or snotstreams).

    Most of what we know about transmission of respiratory pathogens comes from studies of indoor transmission. Partly this is due to the relative safety of the outdoors, but it’s inherently much harder to study outdoor transmission. Nobody knows who is near them on a beach, but indoors, it is often possible to define a population pretty accurately – think of a school, house of worship, hospital, or plane. A lot of information on outdoor transmission comes from sports teams, as one knows who’s on the field, but that tends to be about non-respiratory pathogens, like the 49ers-Rams MRSA incident.

    One county near me just lifted a rule that you not could exercise outdoors more than 5 miles of your home. They even cited cyclists riding alone because they were too far from home. That is not good public health policy. Nor is warning people not to smell lilacs. It’s time to stop and smell the flowers – and use a little common sense.

  19. John Davis says:

    You are very likely right, Paul, and I love tennis. However, as you toss the ball over your head and serve might you wonder if your opponents have the virus and have handled the ball. I have heard the solution is each server (maybe four) bring their own can of balls the nobody handles them other than the server.

  20. Rik Heller says:

    Excellent piece.
    Ecosystems intertwined add complications in thought about spread and practice of not becoming infected. Like so:

    More crowding=more spread.

    More sunshine=less susceptibility per person (Vit Ds)

    More people indoors=more spread. Less AH (absolute humidity)=more spread.

    More means increased likelihood. Now do the math and live well.

  21. Miriam P, Menges says:

    Thank you for helping to clarify what the truth probably is, definitely is, and maybe is! We cannot expect people to abide by recommending a mask, distancing. They do what they think is best and often are totally wrong. How can that be expressed better? Patients do NOT ask their physicians what are the safest propholactic measures to take. They decide for themselves. That scares ME!

  22. Jennifer says:

    This man should really get more air time. Not only does what he say make absolute sense by everything we see out there, but he can back it up by years of education and experience. No, I am am not saying this because what Dr Sax says makes me feel better, but because if this virus was so easily transmitted by walking by someone in the park, a milk container in the grocery, your contaminated clothing or the mail , every single US resident would have already had the virus. I have yet to see the scientific journal paper documenting the case of the person who got the virus from an orange at the store. Thank you Dr Sax!

Leave a Reply

Your email address will not be published. Required fields are marked *

Note: This is a moderated forum. By clicking on the "Submit Comment" button below, you agree to abide by the NEJM Journal Watch Terms of Use.

Our physician bloggers cannot respond to requests for personal medical advice, and recommend patients discuss health issues with their individual physicians.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

HIV Information: Author Paul Sax, M.D.

Paul E. Sax, MD

Contributing Editor

NEJM Journal Watch
Infectious Diseases

Biography | Disclosures | Summaries

Learn more about HIV and ID Observations.