Prevalence of systemic lupus erythematosus and systemic sclerosis in the First Nations population of Alberta, Canada

Objective To estimate the population-based prevalence of systemic lupus erythematosus (SLE) and systemic sclerosis (SSc) in Alberta, Canada, stratified by First Nations status. Methods. Physician billing claims and hospitalization data for the province of Alberta (1994-2007) were used to ascertain cases of SLE and SSc using 3 case definitions. A latent class Bayesian hierarchical regression model was employed to account for the imperfect sensitivity and specificity of billing and hospitalization data in case ascertainment. We accounted for demographic factors, estimating prevalence rates for the First Nations and non-First Nations populations by sex, age group, and location of residence (urban/rural). Results. Our model estimated the prevalence of SLE in Alberta to be 27.3 cases per 10,000 females (95% credible interval [95% CrI] 25.9-28.8) and 3.2 cases per 10,000 males (95% CrI 2.6-3.8). The overall prevalence of SSc in Alberta was 5.8 cases per 10,000 females (95% CrI 5.1-6.5) and 1.0 case per 10,000 males (95% CrI 0.7-1.4). First Nations females over 45 years of age had twice the prevalence of either SLE or SSc relative to non-First Nations females. There was also a trend toward higher overall SLE prevalence in urban dwellers, and higher overall SSc prevalence in rural residents. Conclusion. First Nations females older than 45 years of age have an increased prevalence of either SLE or SSc. This may reflect a true predominance of autoimmune rheumatic diseases in this demographic, or may indicate systematic differences in health care delivery.