When DS was 3 months old he cultured something he apparently brought home from the NICU -- enterbactor cholae and had a horrible cough, so his ID doctor put him on Tobi. Then following month his CF clinic culture showed PA. Those doctors and didn't afterwards. The local CF doctors take patients off tobi after they don't culture it two times in a row; however, the ID doctor said -- he usually keeps his patients on it for a year after the first culture shows up. After a year, he didn't culture it, but the ID doctor said he'd like him on it thru the winter -- so 6 months longer.