Lung infections tend to start out small, and may simmer for a long time before you become symptomatic. Most type of MAC grow very slowly, and can be watched before beginning treatment - BUT they must be monitored regularly and you should be doing airway clearance, nebulizing saline, eating healthy and seeing your doc regularly for monitoring via scans & cultures - waiting without monitoring or doing anything to reduce the level of infection is not usually a wise approach.
Progression includes more & larger nodules, more lobes of the lungs affected, and eventually cavities - which are actually destruction of lung tissue.
Are you waiting and watching? What strategies are you using to reduce the MAC infection?
Sue