In regards to the person talking about HEPA filters suck mold grows in them. MOLD could only grow in a HEPA filter if it was WET! Mold requires MOISTURE and FOOD to grow. That is a fact. So maybe it could grow in a HEPA filter if you have a serious humidity problem in your house. But with the air moving though the filter it should remain dry and will not promote mold growth.
If you do not find the source of your MOLD and stop further growing places for mold, then yes YOU WILL NEVER get rid of the high spore count. As I have said in other posts, people must remember MOLD is always found naturally outdoors and will be in your home. Just don't give them a better home then they have outdoors!!