Ductwork / HVAC System
Sanitize Cooling Coils
Make sure you periodically wipe any biological growth from the coils. Condensation is continually driping off the coils when the HVAC system is running. This condensation provides a perfect place for mold to grow.
In which case, disinfectant should be periodically applied to the coils. You can also use an in-duct ultraviolet (UV) light air purifier, installed near the coil, to destroy mold before it has a change to grow. It will also destroy mold and other microbes that are caught in the filter.
In-duct ultraviolet (UV) light air purifiers are now being specified by the U.S. government's General Services Administration (GSA), to be used in the ductwork (near the cooling coil and drain pan) of all new federal buildings. Their standards document concerning this reads:
"Ultraviolet light (C band) emitters shall be incorporated downstream of all cooling coils and above all drain pans to control airborne and surface microbial growth and transfer."
Drain Pan
This is where the condensation from the cooling coils drips. If you have a flat drain pan, the stagnant water will become infested with mold growth. In which case, a sloped drain pan should be used, so the water runs off to the proper location. You also need to check to make sure that drain lines are flowing properly.
In addition, the drain pan should be cleaned with a disinfectant on occasion, and should be replaced when corrosion becomes significant.
Filters
Change your HVAC filters on a regular basis. If this is not done, the filter itself can become a fertile breeding ground for all the molds and other biological contaminates that are collected. Once this happens, the spores from the mold will multiply, and will be circulated throughout the home or building through the ductwork.