Epidemiology of ANCA-associated vasculitis in Townsville, North Queensland

Aim: The primary aim of the study was to obtain the prevalence of ANCA-associated vasculitis (AAV) in Townsville. A secondary aim was to compare this study with other centres with different latitudes in Australia and New Zealand. A latitudinal variance in disease rates for ANCA-associated vasculitis has been shown in Europe and New Zealand.\ud \ud Methods: The pathology database at Townsville Hospital was respectively searched for all positive ANCA tests between 2009 and 2013. Patient files were reviewed for all positive results to determine whether they met the ACR criteria for granulomatosis with polyangiitis (GPA) or Chapel Hill criteria for microscopic polyangiitis (MPA) or eosinophilic granulomatosis with polyangiitis (EGPA).\ud \ud Results: 5013 ANCA tests were requested at Townsville Hospital in the 5 year study period. 61 patients had positive ANCA results. 23 patients met criteria for ANCA-associated vasculitis with 13 cases of MPA, 6 cases of GPA, 2 cases of EGPA and 2 others. 14 out of those 23 patients lived in the Townsville Health District. Townsville Health District had a population of 230,000 in 2010 giving a prevalence of 61 cases of AAV/million population over 5 years. MPA had a rate of 34/million and GPA 22/million.\ud \ud Conclusions: This study shows lower rates of AAV than other southern hemisphere studies in Christchurch (151/million/5 years) or Australian Capital Territory (148/million/5 years). These results add further evidence to the observed latitudinal difference in disease. The study may have underestimated the disease burden due to a number of factors. Firstly, it did not include a local private hospital and secondly, it did not include cases that had ANCA tests performed at private laboratories or before the study began