What is the clinical significance of filamentous fungi positive sputum cultures in patients with cystic fibrosis?

In patients with cystic fibrosis (CF), the isolation of filamentous fungi, in particular Aspergillus spp. in the respiratory secretions is a common occurrence. Most of these patients do not fulfil the clinical criteria for a diagnosis of allergic bronchopulmonary aspergillosis (ABPA). The clinical relevance of filamentous fungi and whether antifungal therapy should be started in patients with persistent respiratory exacerbations who do not respond to two or more courses of appropriate oral or intravenous antibiotics and in whom no other organisms are isolated from respiratory secretions is a dilemma for the CF clinician. In this article, we review the epidemiology and clinical significance of filamentous fungi in the non-ABPA CF lung, with an emphasis on Aspergillus spp. colonisation (AC), the clinical relevance of Aspergillus spp. positive respiratory cultures and the outcome following antifungal therapy in these patients.