Anti-Bacterial Agents/therapeutic use; Aztreonam/therapeutic use; Cystic Fibrosis/complications; Pseudomonas Infections/drug therapy; Pseudomonas aeruginosa; Administration, Inhalation; Adolescent; Adult; Aged; Anti-Bacterial Agents/administration & dosage; Anti-Bacterial Agents/adverse effects; Aztreonam/administration & dosage; Aztreonam/adverse effects; Child; Chronic Disease; Cystic Fibrosis/microbiology; Double-Blind Method; Female; Forced Expiratory Volume/drug effects; Humans; Male; Middle Aged; Pseudomonas Infections/complications; Quality of Life; Respiratory Function Tests/methods; Respiratory Function Tests/statistics & numerical data; Serum Bactericidal Test/methods; Serum Bactericidal Test/statistics & numerical data; Surveys and Questionnaires; Treatment Outcome; United States; Young Adult