Results of the project FFC#13/2017, have shown that the VBNCs (Viable Non-Cultivable Bacteria) are bacteria in the CF lung that can escape the classical diagnostic cultures, being inactive however still viable. Such bacteria are capable of interrupting their state of quiescence and reactivate, causing relapses and making the respiratory infection chronic. Having developed a specific method of investigation to identify them (a combined techniques of molecular biology-qPCR- and flow cytometry), now researchers want to understand their importance in the clinical history of CF patients. Through this two-year prospective study, which will involve a hundred patients, both VBCNs and other bacteria in the sputum samples collected at each follow-up will be investigated and the role of VBNCs will be evaluated in association with the clinical status of patients and with the evolution of their CF lung disease.