Does geographic location affect incidence of ANCA-associated renal vasculitis in northern Saskatchewan, Canada?

To compare the incidence of renal ANCA-associated vasculitis (AAV) in urban vs more rural populations in northern Saskatchewan, and as a secondary objective to compare time to diagnosis between these geographic areas.

Northern Saskatchewan has a population of 562,882 of which approximately 260 600 live in the major urban area. A pathology database search for renal biopsy reports suggestive of AAV between January 2007 and December 2011 and subsequent chart review yielded 33 new diagnoses of granulomatosis polyangiitis (GPA) or microscopic polyangiitis (MPA). Data extraction included demographics, residential data, serological status, recorded symptom onset and estimations of BVAS, five-factor score (FFS) and vasculitis damage index (VDI).

Of 33 renal AAV cases, 24.2 % (n = 8) lived within the city. The incidence rate for urban residents was 6.1 cases/million/year, and for those residing elsewhere, 16.5 cases/million/year. The odds ratio for the more rural population was 2.69 (95% CI 1.3, 7.5). Mean time to diagnosis was 1.33 (s.d. 0.94) months for urban and 3.52 (s.d. 3.83) months for more rural patients (P = 0.002, 95% CI 0.7, 3.9). Secondary analysis supported these observations with higher BVAS, VDI and FFS scores in patients living outside the urban centre.

The incidence of renal biopsy-proven AAV was higher in patients living in northern Saskatchewan smaller communities and rural settings. A significantly longer time to diagnosis existed for patients outside the urban centre and was associated with poorer BVAS, VDI and FFS scores.