Risk of multiple sclerosis in individuals with infectious mononucleosis: a national population-based cohort study using hospital records in England, 2003-2023.

BACKGROUND: Epstein-Barr virus (EBV) is thought to be a necessary causative agent in the development of multiple sclerosis (MS). Infectious mononucleosis (IM), which occurs up to 70% of adolescents and young adults with primary EBV infection, appears to be a further risk factor but few studies have been highly powered enough to explore this association by time since IM diagnosis. OBJECTIVE: The objective was to quantify the risk of MS in individuals with IM compared with the general population, with particular focus on time since IM diagnosis. METHODS: In this retrospective cohort study using English national Hospital Episode Statistics from 2003 to 2023, patients with a hospital diagnosis of IM were compared with the general population for MS incidence. RESULTS: MS incidence in patients with IM was nearly three times higher than the general population after multivariable adjustment (adjusted hazard ratio = 2.8, 95% confidence interval (CI = 2.3-3.4), driven by strong associations at long time intervals (>5 years) between IM diagnosis and subsequent MS diagnosis. CONCLUSION: While EBV infection may be a prerequisite for MS, the disease process of IM (i.e. the body's defective immune response to primary EBV infection) seems to be, in addition, implicated over the long term.

Clinical trial results in context: comparison of baseline characteristics and outcomes of 38,510 RECOVERY trial participants versus a reference population of 346,271 people hospitalised with COVID-19 in England.

BACKGROUND: Randomised trials are essential to reliably assess medical interventions. Nevertheless, interpretation of such studies, particularly when considering absolute effects, is enhanced by understanding how the trial population may differ from the populations it aims to represent. METHODS: We compared baseline characteristics and mortality of RECOVERY participants recruited in England (n = 38,510) with a reference population hospitalised with COVID-19 in England (n = 346,271) from March 2020 to November 2021. We used linked hospitalisation and mortality data for both cohorts to extract demographics, comorbidity/frailty scores, and crude and age- and sex-adjusted 28-day all-cause mortality. RESULTS: Demographics of RECOVERY participants were broadly similar to the reference population, but RECOVERY participants were younger (mean age [standard deviation]: RECOVERY 62.6 [15.3] vs reference 65.7 [18.5] years) and less frequently female (37% vs 45%). Comorbidity and frailty scores were lower in RECOVERY, but differences were attenuated after age stratification. Age- and sex-adjusted 28-day mortality declined over time but was similar between cohorts across the study period (RECOVERY 23.7% [95% confidence interval: 23.3-24.1%]; vs reference 24.8% [24.6-25.0%]), except during the first pandemic wave in the UK (March-May 2020) when adjusted mortality was lower in RECOVERY. CONCLUSIONS: Adjusted 28-day mortality in RECOVERY was similar to a nationwide reference population of patients admitted with COVID-19 in England during the same period but varied substantially over time in both cohorts. Therefore, the absolute effect estimates from RECOVERY were broadly applicable to the target population at the time but should be interpreted in the light of current mortality estimates. TRIAL REGISTRATION: ISRCTN50189673- Feb. 04, 2020, NCT04381936- May 11, 2020.