Role of real time PCR and specific IgG in identifying CF patients with Aspergillus colonisation

Purpose Aspergillus fumigatus causes significant morbidity in Cystic fibrosis (CF). Adults with CF demonstrate a wide variety of immunopathological responses to A. fumigatus ranging from simple atopy (60%) to allergic bronchopulmonary aspergillosis (ABPA) (15%). The natural history of ABPA is not known and diagnosis in CF remains difficult. Accurate diagnosis allows effective antifungal therapy but it is not known whether colonised and sensitised patients would also benefit from antifungal therapy. A.fumigatus colonisation is common in CF but prevalence varies between studies from 12-57%. This research aimed to accurately identify patients with A.fumigatus colonisation and examine the relationship to sensitisation. Methods Patients were recruited from the Manchester Adult CF Unit and were asked to provide a sputum sample, a blood sample for Aspergillus serology and undergo fungal skin prick tests (SPT). Serological tests included total IgE, specific IgE A.fumigatus and specific IgG A.fumigatus performed by Phadia ImmunoCAP® assay, and A.fumigatus precipitins by counterimmunoelectrophoresis. A commercial Real time PCR kit, MycAssay™ Aspergillus , which utilises molecular beacons targeting the 18S ribosomal unit of Aspergillus spp, was used to detect Aspergillus in CF sputum samples. Sputum PCR was then compared to patient serology. Results 49 patients provided a sputum sample: 15 were PCR positive for Aspergillus species. Within the PCR positive group 2 patients had known ABPA on itraconazole, 7 were sensitised as defined by a positive SPT or specific IgE A.fumigatus, and 6 had no evidence of sensitisation. All PCR positive samples had a positive specific IgG titre (>40mg/L) whereas 41% of PCR negative samples had a positive IgG titre. PCR positive patients had a significantly greater mean specific IgG Aspergillus (PCR positive 93mg/L SE 6.74 vs PCR negative 47mg/L SE 4.44 p=