The association between urbanization and rheumatoid arthritis in Taiwan

To investigate the association between rheumatoid arthritis (RA) and urbanization and compare the medication selection for RA patients in urban vs. rural areas.

RA patients were identified among 1,000,000 random individuals from a 23-million-person nationwide health insurance database, and controls were matched at a 1 : 10 ratio. Taiwan's 359 townships were grouped into 7 urbanization levels. Geographic region and monthly income were also analyzed. Medication use in the most urbanized and less-urbanized areas were also compared.

Rural dwellers had lower odds of having an RA diagnosis. The odds ratio (OR) for level 5 area residents of having an RA diagnosis was 0.62 (95% confidence interval (CI) 0.46 - 0.85; p = 0.002), and they were both 0.76 for level 6 - 7 area residents (95% CI, 0.61 - 0.95 for level 6; p = 0.017 and 0.60 - 0.96 for level 7; p = 0.021) compared to level 1 (the most urban dwellers). The ORs of having a new RA diagnosis were 0.57 (95% CI 0.41 - 0.79, p = 0.001) in eastern Taiwan and 0.33 (95% CI 0.15 - 0.69, p = 0.004) on offshore islands compared to northern Taiwan. No association was found between monthly income and RA. Urban-dwelling RA patients used more tumor necrosis factor-α antagonists (level 1 urbanization; n = 24; 2.3%) than RA patients in less-urbanized areas (level 2 - 7 urbanization n = 30; 1.3%; p = 0.038).

Results of this study suggested that an RA diagnosis and treatment are associated with urbanization.