Rheumatoid Arthritis Disease Activity and Disability Affect the Risk of Serious Infection Events in RADIUS 1

Objective. To determine whether disease activity and disability independently correlate with serious infection event (SIE) risk in a large rheumatoid arthritis (RA) cohort.

Methods. The associations between SIE and Clinical Disease Activity Index (CDAI) and Health Assessment Questionnaire-Disability Index (HAQ-DI) in the Rheumatoid Arthritis Disease-Modifying Antirheumatic Drug Intervention and Utilization Study (RADIUS 1) cohort were evaluated using the Andersen-Gill model (a proportional HR model allowing > 1 event per patient).

Results. Of 4084 patients with 347 SIE, 271 patients experienced ≥ 1 SIE. A 5-unit CDAI increase and 0.4-unit HAQ-DI increase corresponded to an increase in SIE risk with and without covariate adjustments. A 5-unit CDAI increase corresponded with a 7.7% increased SIE risk (adjusted HR 1.077, 95% CI 1.044–1.112, p < 0.0001) and a 0.4-unit HAQ-DI increase with a 30.1% increased risk (adjusted HR 1.301, 95% CI 1.225–1.381, p < 0.0001). Categorical analysis showed that more severe RA activity (even after controlling for disability) and disability were associated with an increased SIE risk.

Conclusion. Increased RA disease activity and disability were each associated with a significantly increased SIE risk in the RADIUS 1 cohort, which could not be completely accounted for by disability.