Trends in population-based incidence and prevalence of juvenile idiopathic arthritis in Manitoba, Canada.

Objective To estimate the incidence and prevalence of juvenile idiopathic arthritis (JIA) in children ages <16 years in the province of Manitoba, Canada, and to determine changes in estimates between 2000 and 2012. Methods JIA cases were ascertained from the administrative health data of Manitoba, using a validated case-finding algorithm. Annual incidence and prevalence rates were estimated using a generalized linear model with generalized estimating equations (GEEs), adjusting for sociodemographic characteristics. Changes in estimates were tested using piecewise regression models. Results A total of 455 cases of JIA prevalence met the inclusion criteria. Sex- and age-adjusted incidence estimates were 14.01 (95% confidence interval [95% CI] 13.52, 14.53) in 2000/2001 and 9.18 (95% CI 8.56, 9.85) in 2010/2011. Prevalence estimates were 65.33 (95% CI 63.87, 66.83) in 2000/2001 and 59.61 (95% CI 58.17, 61.08) in 2010/2011. A linear piecewise model provided the best fit to the data. There was a significant decrease in prevalence over the study period (-0.18 [95% CI -0.35, -0.02]; P = 0.0292) but no statistically significant change in incidence (-0.46 [95% CI -0.94, 0.01]; P = 0.0571). Sex-stratified models revealed a decrease for males in both prevalence (estimate -0.54 [95% CI -0.84, -10.25]; P = 0.0003) and incidence (estimate -1.02 [95% CI -2.02, -0.04]; P = 0.0439); there were no changes for females. Conclusion Few population-based longitudinal epidemiologic studies of JIA have been conducted. Our findings suggested a decrease in overall JIA prevalence, and in incidence and prevalence in men. Further research to validate these findings in other cohorts and to explore factors that contribute to this change will benefit future health care planning for JIA.