The prevalence of Rheumatoid Arthritis in Chile: a nation-wide study performed as part of the National Health Survey (ENS 2016-17).

Objective Genetic and environmental backgrounds influence the development of rheumatoid arthritis (RA). In Latin America epidemiologic data are scarce. We aimed to determine the prevalence of RA in Chile in a population-based study. Methods The National Health Survey was a cross-sectional household survey with a stratified multistage probability sample of 6,233 participants performed between August 2016 and March 2017. A screening instrument for RA was applied to a random sample of 3,700 subjects >30 years old. Positive screening was defined by at least one of the following: (i) 2 swollen joints for at least 4 consecutive weeks (past /present) and/or (ii) a diagnosis of arthritis in the past. Individuals with positive screening had Rheumatoid Factor, Anti-citrullinated protein antibodies, and C-reactive protein measured and clinical examination performed by a rheumatologist. Self-report of doctordiagnosed RA was also performed. Results The screening questionnaire was applied to 2,998 subjects. Seven hundred and thirty-eight (22.1%) had positive screening. Among subjects with positive screening 493 (66%) had a clinical evaluation performed by a rheumatologist. Using ACR/EULAR 2010 classification criteria prevalence was 0.6% (95%CI 0.3, 1.2). Prevalence was higher in female gender. Three point three percent of subjects self-reported having RA. Conclusion According to this national population-based study RA prevalence in Chile is 0.6% (0.3, 1.2), a value similar to what has been found in developed Caucasian countries and slightly lower than some Latin American countries. Self-reporting leads to overestimating RA.