It's not airborne so the only reason would be so many people living in close proximity. If it was airborne it would be a whole different story as the ventilation is shared throughout most condos.
High rise condos have a central air supply (known as "Make Up Air") that continuously brings in fresh outside air (usually from the rooftop, filters it for large particles, and then big fans blow the fresh outside air down shafts and out vents in the hallways.
That fresh air supply pressurizes the hallways and seeps into individual suites under and around the door. The suites are therefore slightly pressurized so they generally do not get or share air from adjoining suites.
So the air is "shared" in that the thousands of cubic feet of fresh outside air that are sucked in from the rooftop are then distributed/shared amongst the hallways and suites.
But the air is not "shared" between suites.
There is a risk of infection if someone with you on the elevator coughs or if someone that is infected touches the elevator button or door handles wth a sneezed hand.. and then you touch it and then touch your nose/mouth etc.
Use something other than your finger (key fob) to touch elevator buttons and use the Handicap Door Openers (with your elbow) if your building has them. And then wash your hands when you get back in your apartment.