Epidemiology of granulomatosis with polyangiitis (Wegener's granulomatosis) in Northern Italy: A 15-year population-based study

Objective: To investigate the epidemiology of granulomatosis with polyangiitis (GPA) over a 15-year period in a defined area of northern Italy. Methods: All patients with incident GPA diagnosed from January 1, 1995 to December 31, 2009 living in the Reggio Emilia area were identified by looking at computerized hospital discharge diagnoses, by contacting Reggio Emilia Hospital physicians and community-based specialists, and by checking the databases of the pathology and the laboratory departments and the Reggio Emilia district database for rare diseases. Patients were classified according to the European Medicines Agency (EMA) algorithm. Patients were followed up from the time of diagnosis until either their death or December 31, 2011. For each case, we identified 20 control subjects from the same geographic area matched for age and gender. Results: A total of 18 patients (7 men and 11 women) with GPA were identified. The overall age- and sex-adjusted incidence rate (IR) was 2.4 per million (95% CI: 1.2-3.5). The mean annual IR increased from 1.7/million/year during 1995-1999 to 3.4 during 2005-2009. The highest IR occurred in females aged 70-79 years (13.5 per million; 95% CI: 5.0-30.0) and in males aged ≥ 80 years (14.9 per million; 95% CI: 2.5-49.4). The prevalence of GPA on December 31, 2009 was 34.3 per million (95% CI: 20.3-54.2). The point prevalence per million increased from 17.8 (95% CI: 7.7-35.1) in 1999 to 34.3 (95% CI: 20.3-54.2) in 2009. Survival among individuals with GPA was significantly reduced compared to that observed in the matched control population (. p <0.001). Conclusion: In the Italian population, GPA is very uncommon and GPA patients have reduced survival.