Mapping the risk of infections in patients with multiple sclerosis: A multi-database study in the United Kingdom Clinical Practice Research Datalink GOLD and Aurum

BACKGROUND: People with multiple sclerosis (pwMS) have an increased risk of infections; risk factors include underlying disease, physical impairment and use of some disease-modifying treatments. OBJECTIVE: To quantify changes in population-level infection rates among pwMS and compare these to the general population and people with rheumatoid arthritis (pwRA), and identify patient characteristics predictive of infections after MS diagnosis. METHODS: We conducted a multi-database study using data on 23,226 people with MS diagnosis from the UK Clinical Practice Research Datalink Aurum and GOLD (January 2000–December 2020). PwMS were matched to MS-free controls and pwRA. We calculated infection rates, and estimated incidence rate ratios (IRR) and 95% confidence intervals (CI) of predictors for infections ⩽ 5 years after MS diagnosis using Poisson regression. RESULTS: Among pwMS, overall infection rates remained stable – 1.51-fold (1.49–1.52) that in MS-free controls and 0.87-fold (0.86–0.88) that in pwRA – although urinary tract infection rate per 1000 person-years increased from 98.7 (96.1–101) (2000–2010) to 136 (134–138) (2011–2020). Recent infection before MS diagnosis was most predictive of infections (1 infection: IRR 1.92 (1.86–1.97); ⩾2 infections: IRR 3.00 (2.89–3.10)). CONCLUSION: The population-level elevated risk of infection among pwMS has remained stable despite the introduction of disease-modifying treatments.