Beside its use as a diagnostic test to identify bacterial pathogens induced sputum has been used to assess lower airway inflammation in CF. While numerous studies have clarified the role of S. aureus and P. aeruginosa in CF lung disease, the role of other emerging bacteria such as Stenotrophomonas maltophilia (SM) and Achromobacter xylosoxidans (AX) species remains largely unclear. IS offers the potential to possibly differentiate between colonisation and infection for the emerging pathogens and to help clarify their role in CF lung disease.