- known or highly suspected bacterial infection (antibiotic treatment to avoid bacterial superinfection may be allowed) - pct ≥ 1μg/l - mechanical ventilation - inability to conduct inhalation therapy - hemodynamic instability with requirement of vasopressor therapy - severe comorbidities interfering with the safe participation at the trial according to the treating physician - pregnancy - systemic immunosuppression

- known or highly suspected bacterial infection (antibiotic treatment to avoid bacterial superinfection may be allowed) - pct ≥ 1μg/l - mechanical ventilation - inability to conduct inhalation therapy - hemodynamic instability with requirement of vasopressor therapy - severe comorbidities interfering with the safe participation at the trial according to the treating physician - pregnancy - systemic immunosuppression