The epidemiology of rheumatoid arthritis in Ontario, Canada

Epidemiologic assessments of sufficiently large populations are required in order to obtain robust estimates of disease prevalence and incidence, particularly when exploring the influence of various factors (age, sex, calendar time). We undertook this study to describe the epidemiology of rheumatoid arthritis (RA) over the past 15 years.

We used the Ontario Rheumatoid Arthritis administrative Database (ORAD), a validated population-based research database of all Ontarians with RA. The ORAD records were linked with census data to calculate crude and age and sex-standardized prevalence and incidence rates from 1996 to 2010. Vital statistics were used to estimate annual all-cause mortality during the study period.

As of 2010, there were 97,499 Ontarians with RA, corresponding to a cumulative prevalence of 0.9%. Age and sex-standardized RA prevalence increased steadily over time from 473 (95% confidence interval [95% CI] 469-478) per 100,000 population (0.49%) in 1996 to 784 (95% CI 779-789) per 100,000 population (0.9%) in 2010. Age and sex-standardized incidence per 100,000 population ranged from 62 (95% CI 60-63) in 1996 to 54 (95% CI 52-55) in 2010. All-cause mortality decreased by a relative 21.4% since 1996.

Over a 15-year period, we observed an increase in RA prevalence over time. This rise may be attributed to the increasing time to ascertain cases (which may have been latent in the population during earlier years of the study), increasing survival, and/or an increase in the aging background population. Incidence appears to be stable.