You can't refuse them because they're in a wheelchair but it's their responsibility to pay for the changes needed to bring the property up to speed with elevators, wheelchair ramps, bathroom handles etc.

New building codes require properties to be elevated before building.

However, landlords need not undertake changes that would seriously impair their ability to run their business, such as installing an elevator to the third floor to accommodate a wheelchair-bound tenant’s wish to live there.?"

But they are predominantly ground floor elevations rather than having them negotiate stairs to a basement or upper floor unit.

If built after 1978, then an elevation certificate is required. 

It says right in the article that people were letting their dogs poop in the halls, elevators, etc....and not even picking it up.

These are higher in elevation than a standard toilet.

There were signs up all over the lobby and in the elevator, and in the laundry rooms all yelling at you.  

And the elevators are dreadfully slow.

As long as the fungal ecology of the indoor environment is consistent with the outside environment, no elevated health risk exists.