To quantify the incremental cost of infections in patients treated with etanercept, adalimumab or infliximab versus abatacept.

Inclusion Criteria:

• 18 years of age and older;
• Have a diagnosis of of rheumatoid arthritis (ICD-9:714x.xx);
• Have been enrolled for at least 6 months for the 6 months assessment and 12 months for the 12 months assessment;
• are enrolled in a health plan between February 2006 and June 2009
• have claims indicating at least one use of either abatacept, etanercept, adalimumab or infliximab for at least 6 months for teh 6 months assessment and 12 months for the 12 months assessment

Exclusion Criteria:

• Patients not continuously eligible for health plan benefits for the same evaluation periods will be excluded
• Patients who are on other biologics in the 6 and 12 month post-index period will be excluded (ex. those in the abatacept cohort will be excluded if they also have claims for etanercept in the 6 and 12 month post-index period).
• Patients on biologics 6 months prior to the biologic index date will also be excluded
• Patients with diagnosis for other non-RA conditions commonly treated with biologics (ex. Crohn's disease) during the 6 month pre-index period.

Commercial health plan members