Secular trends in the incidence and prevalence of rheumatoid arthritis within members of an integrated health care delivery system.

The study objective was to estimate secular trends in the overall incidence rate (IR) and prevalence rate (PR) of rheumatoid arthritis (RA); and subgroup-specific IR and PR by race, ethnicity, and sex in a multi-ethnic population of a large integrated health care delivery system. An ecological study was conducted within the adult population of Kaiser Permanente Southern California health plan. From January 1995 up to and including December 2014, annual IR and PR were calculated separately by race, ethnicity, sex and pooled overall. Depending on the stationarity of each ecological series, annual percentage change in IR and PR was evaluated using auto-regressive integrated moving average models. Average overall IR was 53 [95% confidence interval (CI) 46, 61] per 100,000 person-years. The overall as well as subgroup-specific annual IR of RA were unchanged from 1995 to 2014. In 1995, the overall PR of RA was 59 (44, 74) per 100,000 person-years which increased by 14% (7%, 21%) annually thereafter. The increase in PR in Caucasians was lower as compared to African American, Asian and other race (13% vs 15%, 15%, and 18%, respectively). Compared to non-Hispanic ethnicity, the increase in PR among Hispanic was higher (17% vs 14%). Over the past 2 decades, while the incidence of RA was unchanged, the prevalence had increased significantly overall as well as within every subgroup of race, ethnicity, and sex.