Power of national economy, disease control and employment status in patients with RA-an analytical multi-site ecological study.

In rheumatology, sufficient disease control is a central part of the treatment concept. However, modern treatment strategies are associated with a substantial economic burden for health care systems. Ecological studies offer the unique opportunity to analyse differences between groups as well as group level effects. In the present analytical multi-site ecological study, we investigated whether more powerful national economies as measured by the gross domestic product per capita (GDPpc) are associated with better disease control in RA patients as measured by the disease activity score 28 (DAS28). We used aggregated data on RA patients from the recently published COMORA study as well as the World Health Organization database. There was a strong negative correlation between DAS28 and GDPpc (r = -0.815; p = 0.0002). Adjustment for sex, smoking status, disease duration or current employment status did not significantly change this association. There was a strong, negative correlation between DAS28 and age (r = -0.870; p < 0.001) and a strong, positive correlation between GDPpc and age (r = 0.737; p = 0.002). Adjustment for age reduced the regression coefficient (DAS28/GDPpc) to -0.000018 (p = 0.054). There was a negative correlation between DAS28 and current employment status (r = -0.642; p = 0.008) and a positive correlation between GDPpc and employment status (r = 0.722; p = 0.002). In conclusion, there is evidence of an association between disease control and GDPpc. This association is alleviated after adjustment for age. Of note, in countries with higher GDPpc, a higher proportion of RA patients are currently employed. This is true despite the fact that RA patients in countries with higher GDPpc are also older.