Patients with cystic fibrosis, a history of colonization with Gram negative bacteria due to structural damage to the respiratory tract, malfunction of the digestive tract, life expectancy of less than 1 month due to underlying diseases, infections other than pneumonia needing antibiotic treatment, severe immunosuppression (neutropenia (<0,5 x 109 / l) or a CD4 count < 200 / mm3) and needing mechanical ventilation in an intensive care unit were excluded.