I think you may have a tiny bit of information that has been altered from truthful facts of aircraft system operation by someone who does not know jack a bout it but really tied to impressed you knowingly feeding your phobias.
Compressed air is tapped from the 14th stage of compression from each engine ( end of the N-1 fan section this is low pressure air ) and routed to the air conditioning packs ( left and right ), the temperature is lower from +230*C to crew commanded pre-set of +2-15*C then routed into the cabin, the out-flow safety value regulates (modulates) the internal pressure of the aircraft from Sea Level to about 8,000 ft. depending on aircraft altitude, due to the extremely high volume of airflow each molecule of air will be relieved overboard every 32-78 seconds depending on aircraft altitude and pressurization requirements. This is why the air is so dry at about 2 -6% humidly. The out-flow safety valve are “fail safe open” to prevent rupturing the fuselage like over blowing up a balloon, being why a integrity breach of the pressurized fuselage can be so catastrophe, as in the MH-17 shoot down, BE NOTED, it takes about 1 ½ - 2 seconds for the cabin to equalized with the outside atmosphere at cruise, not 5 minutes like TV and movies, been there, got the ruptured ears drums, thank you. Now the physical location on the airframe of the out-flow valve will dictate internal airflow path of the flow overboard, as in older aircraft it was in the back, REMEMBER, smokers sat in the back, non-smokers sat up front smoke free ? DAH Therefore if a person is sitting near the outflow valve and another person just happens to have something contagious up airflow maybe, maybe you will get it. That is why the 1st question investigators ask, “What seat were they in ?” I don’t know about anyone else here, but I want $1000 on those odds.
Just saying, I’m pretty damn sure what I just typed, I in-flight managed the system 15 years before the Auto-controllers were perfected, and they work the same damn way. It isn’t like a car air conditioner you can turn on and off, its primary purpose is pressurization, the secondary purpose is you make is warm and cozya.
Sometimes when I read mistruths it fly’s all over me like this, other times I just think to poster don’t know shit or full of it and just don’t care lmao