“Should I assume that means that in my building there is no chance of spread through ductwork?”
My guess would be it could probably be spread to the same people in your home who breath the same air. Likewise people who live in different apartments that use the same system could contract it. JMHO
Supposedly the disease does not spread through the air—touch of a surface (living or non-living) is required.
Wearing gloves (not masks) is your best defense.
You can investigate this further to confirm or deny.