Characterisation of the nasal microbiota in granulomatosis with polyangiitis.

Objectives: Prior studies have suggested a potential link between nasal microbes and granulomatosis with polyangiitis (GPA; Wegener's), but these studies relied on culture-dependent methods. This study comprehensively examined the entire community of nasal microbiota (bacteria and fungi) in participants with GPA compared with healthy controls using deep sequencing methods.

Methods: 16S rRNA and internal transcribed spacer gene sequencing were performed on nasal microbial DNA isolated from nasal swabs of 60 participants with GPA and 41 healthy controls. Alpha and beta diversity were assessed as well as the relative abundance of the most abundant bacterial and fungal taxa. The effects of covariates including disease activity and immunosuppressive therapies on microbial composition were evaluated.

Results: Compared with controls, participants with GPA had a significantly different microbial composition (weighted UniFrac p=0.04) and lower relative abundance of and (for both, false discovery rate-corrected p=0.02). Disease activity in GPA was associated with a lower abundance of fungal order compared with participants with GPA in remission (p=0.04) and controls (p=0.01). Use of non-glucocorticoid immunosuppressive therapy was associated with 'healthy' nasal microbiota while participants with GPA who were off immunosuppressive therapy had more dysbiosis (weighted UniFrac p=0.01). No difference in the relative abundance of was observed between GPA and controls.

Conclusions: GPA is associated with an altered nasal microbial composition, at both the bacterial and fungal levels. Use of immunosuppressive therapies and disease remission are associated with healthy microbial communities.