A clinic visit/culture is usually my first step. Depending on what grew during your last culture (I get them every 2-3 months) might give doc an idea what med to try first (if you have several strains that have different sensitivities/resistances). Depending on other symptoms, steroids, increased nebs, etc. Follow up in a few days after antibiotics begin, to assess if they are working. That is usually the first few days' worth of "work" when I feel an exacerbation coming on.