Serious infections in patients with relapsing and progressive forms of multiple sclerosis: A German claims data study

Background: People with multiple sclerosis (pwMS) have a higher risk of serious infection (i.e., infection-related hospitalizations) than people without MS. Few studies have explored the risk of serious infections by MS phenotype in a real-world setting. This retrospective study compared the incidence of serious infections among people with relapse remitting MS (RRMS), primary progressive MS (PPMS), and secondary progressive MS (SPMS). Methods: Adult pwMS were selected from a German claims database, based on one inpatient or two outpatient diagnoses of MS (ICD-10 G35) by a neurologist from 01/01/2016 to 12/31/2018. Three cohorts (RRMS, PPMS, SPMS) were identified based on codes for MS subtypes included in the German Modification of the ICD-10 system. A fourth cohort of unspecified MS patients combined those with conflicting MS subtype diagnoses and multiple unspecified codes for MS. Serious infections were defined as hospitalizations for which infections were selected as the primary inpatient diagnosis. Infections were identified from a basket of ICD-10 codes distributed across 11 main categories, according to possible pathogen (e.g., other bacterial diseases [A30-A49]) or anatomical location (e.g., urinary tract infection [N39.0]). Multiple infections were counted if an interval of at least 60 days was recorded between episodes. Serious infections were counted from index (i.e., first recorded MS code) until the end of the study period or death. Incidence rates (IRs) were reported per 100 patient years (PY).Results: A total of 4,250 pwMS (RRMS: 2,307, PPMS: 282, SPMS: 558, unspecified MS: 1,135) were included; 32 patients progressed from RRMS to SPMS during the follow-up period. Mean (SD) age at baseline was 46.6 (13.6), 61.9 (12.4), and 62.5 (11.8) years in patients with RRMS, PPMS, and SPMS, respectively. Most pwMS were female (RRMS 74.8%, PPMS 62.1%, SPMS 67.4%). Progressive pwMS were more likely to have at least 1 co -morbidity (PPMS 87.2%, SPMS 87.5%) compared to those with relapsing MS (61.9%). Most RRMS patients received disease-modifying therapy during follow-up (82.1%), while less than half of progressive MS patients did (PPMS 23.8%, SPMS 31.4%). Over a mean (SD) follow-up period of 3.5 (0.8) years, the IR of serious infections per 100 PY was higher in progressive MS cohorts (PPMS 13.5 [11.3-16.1], SPMS 13.6 [12.0-15.3]) than in the RRMS group (3.4 [3.0-3.7]). Yearly IRs remained stable over time in each cohort. Where anatomical location was specified, respiratory (2.0 per 100 PY) and genitourinary (1.9 per 100 PY) infections were most common. Across all subtypes, higher rates of serious infections were observed in men and older patients. Conclusion: Progressive MS, older age and male sex are associated with an increased risk of serious infections. Overall, respiratory and genitourinary infections were the most commonly reported serious infections.