Why do people workout when they are sick???

Today in spin class there was a gal who was clearly sick. She started with a hacking cough before the class even started. A guy in the class opened the door to get some fresh air & that seemed to make it worse for her(He didn't do it with those intentions--it was just getting hot in the room). The instructor a few moments later got off her bike & closed the door that he just opened. She turned to the sick gal & said, "If you are sick, you shouldn't be by the cold air." UGGG!! It gets hot in there!! Oh well, better workout for us! I guess I'm not showing too much of a good side of me here...but come on here! I am such a germ-a-phobe!! I'm glad that I was not next to her...but it has to make me wonder---did the workout really make her feel better? I once watched a 60 minutes about germs in gyms. What an eye-opener! Anyways....despite the germ infested room, it was a really GREAT workout!!!