I am a school teacher and have had 4 days off sick in 25 years. I consider that I have an awesome immune system for a 53 year old. I did the old school SSB HV from a few years ago (the really hard one) and survived. I then started the SPBHV and within 2 weeks workouts like Wilhelm+5 and Avalanche spire+3 made me v ill and coincided with a big loss of weight as I couldn’t eat enough to keep up with the training…the old HV builds were brutal I had flu for 10 days - 3 days off work and nearly fainted in a parents evening…I now use my brain - I can do HV, I can do intensity…just not both 
I think this study is more about group class environments and how many particles are exhaled at intensity leading to contagious infection. That’s different than what you’re describing, which is stress and fatigue leading to a weaker immune system. Both make it more likely to get sick but they’re two different things.
But related to your experience, I swam ~20hr/wk in high school and I would be pretty healthy all year round but every year or 2 I would get a nasty stomach flu the weekend after our big December meet. A combo of huge chronic training stress, 3 day swim meet with 100s of people, and then finally rest would lead to my body catching something and I would get real sick.
Oh well that’s good - the only other occupant of my pain cave on a regular basis is my 
so I should be safe from future infections…although while watching me I just get the impression she is just reinforcing her view that they are the far superior species and sleeping 20 hours/day is the way to go from an evolutionary standpoint 
Surely the rate at which it increases is related to how hard the subject is breathing. Which is tied to how high their VT1 is, which for most males moderately trained is more than 2W/Kg. Below VT1 your breathing is pretty much the same as when at rest.
Plus the assumption is the person is infected, is asymptomatic, it’s a respiratory illness, the virus is in their lungs / airways, the exerciser doesn’t realise anything is wrong and it doesn’t impact their ability to exercise at higher intensities.
Added per your request. Thanks for checking and helping get useful titles for our topics 
The rate of transmission increase is what they are studying, to move from assumption into knowledge.
The outcome would allow them to determine what risk increase in disease transmission* there is between a room of people doing not much, a room of people doing low intensity exercise and a room of people doing high intensity exercise.
I would expect this might be so that some gyms can argue to stay open in the next pandemic, if I were a cynic.
And having read the abstract beyond the article:
It is not studying risk of infection.
It is not studying risk of transmission of infectious disease during exercise.
In fact it’s not studying anything in the titles of the article, it’s a simple measurement of the increase in aerosol particles exhaled during high intensity exercise
That is all. It’s interesting to have stats but no conclusions can be drawn, and the authors are doing more studies.
Strange place to publish as well, given it has no neurological connection at all.
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It looks like a very low volume science news website, and although it seems harmless I am always cynical when a first time poster like @John_Potter does this sort of thing, so it would be good to hear from him?
Getting people to visit low volume sites or malware infected sites is a paid job after all.