Antirheumatic treatment, disease activity and risk of Staphylococcus aureus bacteraemia in rheumatoid arthritis: a nationwide nested case–control study

OBJECTIVES: To assess how biological disease-modifying antirheumatic drugs (bDMARDs), glucocorticoids and disease activity affect risk of Staphylococcus aureus bacteraemia (SAB) in patients with rheumatoid arthritis (RA). METHODS: In a nationwide cohort of patients with RA from the DANBIO registry, we conducted a nested case–control study including first-time microbiologically verified SAB cases from 2010 to 2018 and incidence density matched controls (1:4 by sex, age). We interlinked Danish registries and identified antirheumatic treatments, RA-specific clinical characteristics, comorbidities and socioeconomic status. The relative risk of SAB was assessed by adjusted ORs with 95% CIs and number needed to harm (NNH) reflected the absolute risk. RESULTS: Among 30 479 patients, we identified 180 SAB cases (incidence rate: 106.7/100 000 person-years) and matched 720 controls (57% women, median age 73 years, IQR: 65–80). Risk of SAB was increased in current (OR 1.8 (95% CI 1.1 to 3.2)) and former bDMARD users (OR 2.5 (95% CI 0.9 to 7.0)), and in current users of oral glucocorticoids ≤7.5 prednisolone-equivalent mg/day (OR 2.2 (95% CI 1.3 to 4.0) and >7.5 mg/day (OR 9.5 (95% CI 3.9 to 22.7)) (non-use as reference). ORs for moderate/high disease activity compared with remission were 1.6 (95% CI 0.8 to 3.3)/1.5 (95% CI 0.6 to 4.3). Risk was increased in patients with longstanding RA (>10 years vs ≤3 years, OR=2.4 (95% CI 1.1 to 5.3)). The NNH was 1172(95% CI 426 to 9374) for current use of bDMARDs and 110(95% CI 43 to 323) for glucocorticoids >7.5 mg/day. CONCLUSION: We identified a dose-dependent increased risk of SAB in patients with RA currently using oral glucocorticoids. Daily use of >7.5 mg appeared to be a clinically relevant risk factor, whereas the absolute risk was low for bDMARDs. No clear impact of disease activity was found.