Infections in patients diagnosed with multiple sclerosis: A multi-database study

•MS patients have higher incidence of any infection than non-MS patients.•Rate of hospitalized infection is >2 times higher.•Rate of urinary tract infection is 2 times higher with a stronger effect in males. Recent data on the rates of infections among patients with multiple sclerosis (MS) are sparse. The objective of this study was to quantify incidence of infections in patients with MS compared with a matched sample of patients without MS (non-MS). This study was conducted in two separate electronic medical databases: the United States Department of Defense (US-DOD) military health care system and the United Kingdom's Clinical Practice Research Datalink GOLD (UK-CPRD). We identified patients with a first recorded diagnosis of MS between 2001 and 2016 (UK-CPRD) or 2004 and 2017 (US-DOD) and matched non-MS patients. We identified infections recorded after the MS diagnosis date (or the matched date in non-MS patients) and calculated incidence rates (IRs) and incidence rate ratios (IRRs) with 95% confidence intervals (CIs) by infection site and type. Relative to non-MS patients, MS patients had higher rates of any infection (US-DOD IRR 1.76; 95% CI 1.72–1.80 and UK-CPRD IRR 1.25; 95% CI 1.21–1.29) and a two-fold higher rate of hospitalized infections (US-DOD IRR 2.43; 95% CI 2.23–2.63 and UK-CPRD IRR 2.00; 95% CI 1.84–2.17). IRs of any infection were higher in females compared with males in both MS and non-MS patients, while IRs of hospitalized infections were similar between sexes in both MS and non-MS patients. The IR of first urinary tract or kidney infection was nearly two-fold higher in MS compared with non-MS patients (US-DOD IRR 1.88; 95% CI 1.81–1.95 and UK-CPRD IRR 1.97; 95% CI 1.86–2.09) with higher rates in females compared with males. IRs for any opportunistic infection, candidiasis and any herpes virus were increased between 20 and 52% among MS patients compared with non-MS patients. IRs of meningitis, tuberculosis, hepatitis B and C were all low. MS patients have an increased risk of infection, notably infections of the renal tract, and a two-fold increased risk of hospitalized infections compared with non-MS patients.