Infections in patients with multiple sclerosis: A national cohort study in Sweden.

Background: Multiple sclerosis (MS) patients have an increased risk of infections, but few population-based studies have reported infections occurring in MS in the years immediately after diagnosis.

Objective: To explore incident infections in MS, stratified by age and sex.

Methods: In a Swedish population-based cohort study 6602 incident MS patients (aged ≥18 years), matched at diagnosis with 61,828 matched MS-free individuals were identified between 1st January 2008 and 31st December 2016, using national registers. Incidence rates (IR) and incidence rate ratios (IRR) with 95% CI were calculated for each outcome.

Results: The IRRs were 2.54 (95% CI 2.28-2.83) for first serious infection and 1.61 (1.52-1.71) for first non-serious infection. Compared with MS-free individuals, MS patients had higher IRs for skin, respiratory/throat infections, pneumonia/influenza, bacterial, viral, and fungal infections, with the highest IRR observed for urinary tract/kidney infections (2.44; 2.24-2.66). The cumulative incidence for most of these infections was higher among MS patients than MS-free individuals, both 0 to <5 and 5 to <9 years after index date.

Conclusions: The burden of infections around the time of MS diagnosis and subsequent infection risk, underscore the need for careful considerations regarding the risk-benefit across different disease-modifying therapies.