Serious infection risk in older adults with RA receiving biologic or targeted synthetic DMARDs: the role of age at disease onset

Background: Older age is a risk factor for serious infection (SI) associated with biologic or targeted synthetic DMARDs (b/tsDMARDs) use in rheumatoid arthritis (RA). Among older adults with RA, one-third are diagnosed at ⩾60 years (late-onset RA, LORA), while others are diagnosed earlier (young-onset RA, YORA). LORA is characterized by a more acute onset and heightened inflammatory burden due to age-related immune dysregulation. Whether RA onset age independently affects infection risk with b/tsDMARDs remains unclear. Objective: Evaluate SI risk in older adults with RA initiating b/tsDMARDs, stratified by RA onset age: LORA versus YORA. Design: Retrospective cohort study using prospectively collected registry data. Methods: From FORWARD, the National Databank for Rheumatic Diseases (2001–2019), we identified RA patients aged ⩾60 years who initiated (1) anti–TNF then (2) subsequent non-TNF b/tsDMARDs. Patients were categorized as LORA versus YORA and matched using kernel-based propensity scores. SI was defined as an infection requiring hospitalization, intravenous antibiotics, or death. Multivariable Cox models estimated the risk of SI in LORA versus YORA. Results: Among 1379 LORA and 2727 weighted YORA patients initiating anti-TNF therapy, the crude incidence of SI was 28.2 and 20.5 per 1000 person-years. In adjusted models, LORA was not associated with increased anti-TNF-related SI risk compared to YORA (HR 0.82, 95% CI 0.63–1.02). Among 198 LORA and 675 weighted YORA patients subsequently initiating non-TNF b/tsDMARDs, the crude incidence of SI was 17.3 versus 19.5 per 1000 person-years. In adjusted models, LORA was not associated with increased non-TNF related SI risk (aHR 0.81, 95% CI 0.31–2.12). Across cohorts, older age was independently associated with increased SI risk. For anti-TNF, prior SI and recent long-term glucocorticoid use, and for non-TNF, HAQ disability were also associated with SI. Conclusion: Age at RA onset was not independently associated with SI risk following b/tsDMARD initiation. Risk stratification should prioritize functional status and treatment history.