As Liz said an exacerbation can be caused by many things but just wanted to mention my experience of taking one of the standard broad spectrum antibiotics usually prescribed (Augmentin) and the fact that it did not work and what that might mean. I think everyone should make sure they have been screened for Pseudo since catching it early is so crucial and since developing it in the chronic form is so terribly impactful to ones health. And in my case a special test had to be ordered which I was not aware of. I had assumed I was screened for "everything" with the usual sputum testing. Best to just check it all out with your Pulmo.