The U.S. is back up to 33 new COVID-19 cases per 100K population per day, up 8% over the past seven days. It now looks as if the Northeast region — the leader for the Omicron-II wave — has peaked. That suggests that the U.S. as a whole should not be far behind. The current, stable rate of new cases in the U.S. is the result of continued increases in most of the country being offset by reductions in the Northeast and Midwest regions.
Data source for this and other graphs of new case counts: Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 5/26/2022, from https://github.com/nytimes/covid-19-data.” The NY Times U.S. tracking page may be found at https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html
Here’s the Northeast by state, where the peak continues to shape up nicely. As they were the leaders on the up-slope of this wave, they should be the bellwethers for the peak.
Extreme aerosol emissions from intense aerobic exercise
One of the earliest U.S. COVID-19 super-spreader events occurred at a church choir practice in Washington State. More than 50 persons (of the roughly 60 in attendance) were infected, and two died.
The terrible thing about this event is that they did everything “right” according to then-current CDC guidance. But this was still the period during which the CDC was in denial about aerosol (airborne) transmission of COVID-19. At that time, the CDC was still telling people that COVID spread via large droplets that rapidly fell out of the air. Accordingly, the official party line was that if people stayed 6′ apart, all would be well and there would be no transmission of COVID-19. No need for masks, ventilation, or other measures. If you read the CDC’s official write-up about that event, they are still in denial, and per the existing, absolutely implausible writeup, that an entire roomful of persons was sickened by one index case because they failed to stay 6′ apart.
Putting the CDC’s past intransigence behind us, it’s now well-established that COVID-19 spreads via aerosols (tiny droplets that can float through the air). We know that certain people (“superemitters”) and certain activities greatly increase emission of those aerosol droplets. And, in particular, we know that singing produces as much aerosol emissions as coughing. This is why some countries (e.g., Germany) and many U.S. mainstream churches banned singing in church for the duration of the emergency phase of the pandemic (see e.g. Post #678, or search this site for “singing”).
In hindsight, then, it’s no mystery why this choral practice created a superspreader event, as did many similar situations around the world. It as if nearly every first-world country had at least one major church-based super-spreader event, e.g. Post #679).
You can extend that to any situation with crowds and loud talking. Plausibly, this is why going to a bar seems to have been the most dangerous activity possible for spread of COVID-19, and why bars were always the first sites to be shut down when COVID-19 restrictions were in place. Followed by indoor dining. As it turns out, sipping a drink and talking loudly is just about the worst thing you can do in terms of aerosol emissions (Post #723).
If talking loudly increases aerosol emissions (Post #585), and singing does the same, it should come as no great shock that breathing heavily likely increases aerosol emissions as well. This is probably why many lists rated “working out at a gym” as a relatively high-risk activity during the pandemic (Post #811).
Based on reporting in yesterday’s NY Times, research now shows definitively just how much intense aerobic exercise increases aerosol emissions. This research, published in the Proceedings of the National Academies of Science,found the aerosol emissions increased well over 100-fold at maximal exercise rate, compared to emissions at rest. My recollection is that this is modestly higher than was found for singing or coughing. Thus, I believe that working out at your maximum aerobic capacity — breathing as hard as you can breathe — increases your aerosol emissions more than any other activity measured so far. The upshot is that high-intensity indoor group exercise is likely among the most dangerous activities for spread of COVID-19.
The research explicitly notes that emissions during intense exercise are far higher than emissions during loud speech. For a given density (persons per square yard), and given level of ventilation, from the standpoint of COVID-19 transmission, you’re safer in a bar than in an aerobics class.
The article shows that the biggest increase occurs when you push really hard. Moderate aerobic exercise pushes up aerosols somewhat. But the big increase occurs when you are pushing yourself as hard as you can. More-or-less, emissions are a function of how hard you breathe. And, interestingly, trained athletes — with higher aerobic capacity — are capable of emitting more aerosols.
Source: Adapted from “Aerosol particle emission increases exponentially above moderate exercise intensity resulting in superemission during maximal exercise”, Benedikt Mutsch, Marie Heiber , Felix Grätz , Rainer Hain et al, PNAS May 23, 2022m https://doi.org/10.1073/pnas.2202521119
There’s a clear policy implication here for Virginia and likely many other states. When mask mandates were imposed for indoor public spaces, Virginia made an exception for individuals using cardio equipment in a gym. In the gym my wife and I (used to, and maybe will again) use, you had to wear a mask walking around, using the weights, and so on. But you did not have to wear one while using the cardiovascular equipment or otherwise engaging in intense aerobic exercise. (Though, to be clear, I continued to wear one in that situation for my own protection, because breathing deeply is also the best way to inhale aerosolized virus directly to the locations where it can take hold most effectively.)
Based on this research, that’s entirely backwards. It’s the people using the cardio equipment that pose the greatest threat to others, and for whom mandatory masking would generate the greatest public health benefit per person.
Given that we’ve all put this behind us, I don’t expect to see any changes in policy. But if — as many expect — we have a winter COVID-19 wave, this research provides a reason for the cautious among you to skip the indoor aerobics when case counts are up. A room full of people breathing heavily from intense cardio exercise is probably not a room you want to be in during an airborne pandemic.
