Prevalence and incidence of rheumatoid arthritis in South Korea.

Several studies of rheumatoid arthritis (RA) incidence and prevalence indicate that occurrence of the disease varies significantly among different populations. We aimed to estimate the prevalence and incidence of RA in South Korea. We used Korean National Health Insurance (NHI) claims data to estimate the prevalence of RA in 2007-2009 and the incidence of RA in 2008. On the basis of our previous validation study, the presence of RA was defined by the diagnostic code for RA with biologic or non-biologic disease-modifying anti-rheumatic drugs in the same claim in each year. To estimate the incidence of RA, we identified cases of RA in 2008 and set the 12-month period prior to 2008 as a disease-free period. Among the incident case of 2008, only patients who continued treatment in 2009 were defined as true incident case of RA in 2008. The corresponding prevalence estimates were 0.26 % (95 % CI 0.25-0.27) in 2006, 0.27 % (95 % CI 0.26-0.28) in 2007, and 0.27 % (95 % CI 0.26-0.28) in 2008. The incidence of RA in 2008 was estimated at 42/100,000 (95 % CI 29.3-54.7) in the general population of South Korea. Data gathered nationwide through the NHI yielded estimates of RA prevalence and incidence in South Korea. This study is the first report of nationwide prevalence and incidence of South Korea and those are comparable to values for other countries in Asia.