1. Positive respiratory culture (sputum, BALF, or deep pharyngeal culture) in the past 3 months for P. aeruginosa. Those who are culture positive for both P. aeruginosa and additional bacteria (S. aureus, H. influenzae) would also be eligible (but see microbiologic exclusions below). Children with either first isolate or chronic/repeated P. aeruginosa infection are eligible.