Epidemiology of primary systemic vasculitis in the Australian Capital Territory and south-eastern New South Wales

The aim of the study was to determine the epidemiology of primary systemic vasculitis in the Australian Capital Territory and the surrounding rural region between 1995 and 2005.

Cases were ascertained by a medical record search according to international consensus classification criteria. For antineutrophil cytoplasmic antibody-associated vasculitides, ascertainment was corroborated by a search of all positive antineutrophil cytoplasmic antibody serology during the study period. Denominators were obtained from region-specific census data collected during the study period. Prevalence, incidence and patient characteristics for primary systemic vasculitides were determined for two 5-year periods, 1995-1999 and 2000-2004.

We identified 41 cases of primary systemic vasculitides (Wegener's granulomatosis (WG), microscopic polyangiitis (MPA), Churg-Strauss syndrome or polyarteritis nodosa) between 1995 and 1999 and 67 between 2000 and 2004, giving prevalences of 95/million (95% confidence interval (CI) 76.9-116.1) and 148/million (95%CI 125.1-173.9), respectively. Annual incidence was similar in both periods (approximately 17/year per million adult population). Disease-specific incidences (per million per year) for each of the two periods were 8.8 and 8.4 for WG, 2.3 and 5.0 for MPA, 2.3 and 2.2 for Churg-Strauss syndrome and 2.3 and 1.1 for polyarteritis nodosa. The rural incidence of MPA was 13.9 (95%CI 7.7-23.5) compared with 1.6 (95%CI 0.2-7.2) in the city and there was a trend towards a higher incidence of WG in rural than urban areas.

The overall incidence of primary systemic vasculitides is similar to that reported from other developed countries. WG is more common in south-eastern Australia than in southern Europe, whereas MPA is less common. There was a trend towards higher incidence of antineutrophil cytoplasmic antibody-associated vasculitides in rural than urban areas.