I think it may be premature to jump to a discussion of MAC, especially if a single course of antibiotics helped, and because a runny nose is not necessarily characteristic. It could still possibly be many other things including sinusitis, allergies, and other lung infections.

As step one I would recommend consulting a pulmonologist to have a complete health history, lung x-rays, and if indicated a CT scan. If these indicate infection, the doc will possibly order a mucus specimen. This test is sent to a special lab for culturing, and takes 4-6 weeks to see if there is MAC, then further testing to determine what drugs will be effective. The course of treatment is 1.5 years or longer.

Sue