Hospital-diagnosed infections before age 20 and risk of a subsequent multiple sclerosis diagnosis.

The involvement of specific viral and bacterial infections as risk factors for multiple sclerosis has been studied extensively. However, whether this extends to infections in a broader sense is less clear and little is known about whether risk of a multiple sclerosis diagnosis is associated with other types and sites of infections such as the CNS. This study aims to assess if hospital-diagnosed infections by type and site before age 20 years are associated with risk of a subsequent multiple sclerosis diagnosis and whether this association is explained entirely by infectious mononucleosis, pneumonia, and CNS infections. Individuals born in Sweden between 1970 and 1994 were identified using the Swedish Total Population Register (n = 2 422 969). Multiple sclerosis diagnoses from age 20 years and hospital-diagnosed infections before age 20 years were identified using the Swedish National Patient Register. Risk of a multiple sclerosis diagnosis associated with various infections in adolescence (11-19 years) and earlier childhood (birth-10 years) was estimated using Cox regression, with adjustment for sex, parental socio-economic position, and infection type. None of the infections by age 10 years were associated with risk of a multiple sclerosis diagnosis. Any infection in adolescence increased the risk of a multiple sclerosis diagnosis (hazard ratio 1.33, 95% confidence interval 1.21-1.46) and remained statistically significant after exclusion of infectious mononucleosis, pneumonia, and CNS infection (hazard ratio 1.17, 95% confidence interval 1.06-1.30). CNS infection in adolescence (excluding encephalomyelitis to avoid including acute disseminated encephalitis) increased the risk of a multiple sclerosis diagnosis (hazard ratio 1.85, 95% confidence interval 1.11-3.07). The increased risk of a multiple sclerosis diagnosis associated with viral infection in adolescence was largely explained by infectious mononucleosis. Bacterial infections in adolescence increased risk of a multiple sclerosis diagnosis, but the magnitude of risk reduced after excluding infectious mononucleosis, pneumonia and CNS infection (hazard ratio 1.31, 95% confidence interval 1.13-1.51). Respiratory infection in adolescence also increased risk of a multiple sclerosis diagnosis (hazard ratio 1.51, 95% confidence interval 1.30-1.75), but was not statistically significant after excluding infectious mononucleosis and pneumonia. These findings suggest that a variety of serious infections in adolescence, including novel evidence for CNS infections, are risk factors for a subsequent multiple sclerosis diagnosis, further demonstrating adolescence is a critical period of susceptibility to environmental exposures that raise the risk of a multiple sclerosis diagnosis. Importantly, this increased risk cannot be entirely explained by infectious mononucleosis, pneumonia, or CNS infections.

Xu Y ，Smith KA ，Hiyoshi A ，Piehl F ，Olsson T ，Montgomery S ... -  《-》

Association of Infectious Mononucleosis in Childhood and Adolescence With Risk for a Subsequent Multiple Sclerosis Diagnosis Among Siblings.

Xu Y ，Hiyoshi A ，Smith KA ，Piehl F ，Olsson T ，Fall K ，Montgomery S ... -  《JAMA Network Open》

Multiple sclerosis after infectious mononucleosis.

Nielsen TR ，Rostgaard K ，Nielsen NM ，Koch-Henriksen N ，Haahr S ，Sørensen PS ，Hjalgrim H ... -  《archives of neurology》

Siblings reduce multiple sclerosis risk by preventing delayed primary Epstein-Barr virus infection.

Epstein-Barr virus infection, and perhaps almost exclusively delayed Epstein-Barr virus infection, seems to be a prerequisite for the development of multiple sclerosis. Siblings provide protection against infectious mononucleosis by occasionally preventing delayed primary Epstein-Barr virus infection, with its associated high risk of infectious mononucleosis. Each additional sibling provides further protection according to the age difference between the index child and the sibling. The closer the siblings are in age, the higher the protection, with younger siblings being more protective against infectious mononucleosis than older siblings. If the hypothesis that delayed Epstein-Barr virus infection is necessary for the development of multiple sclerosis is true, then the relative risk of multiple sclerosis as a function of sibship constellation should mirror the relative risk of infectious mononucleosis as a function of sibship constellation. Such an indirect hypothesis test is necessitated by the fact that age at primary Epstein-Barr virus infection is unknown for practically all people who have not experienced infectious mononucleosis. In this retrospective cohort study using nationwide registers, we followed all Danes born during the period 1971-2018 (n = 2 576 011) from 1977 to 2018 for hospital contacts with an infectious mononucleosis diagnosis (n = 23 905) or a multiple sclerosis diagnosis (n = 4442), defining two different end points. Relative risks (hazard ratios) of each end point as a function of sibship constellation were obtained from stratified Cox regression analyses. The hazard ratios of interest for infectious mononucleosis and multiple sclerosis could be assumed to be identical (test for homogeneity P = 0.19), implying that having siblings, especially of younger age, may protect a person against multiple sclerosis through early exposure to the Epstein-Barr virus. Maximum protection per sibling was obtained by having a 0-2 years younger sibling, corresponding to a hazard ratio of 0.80, with a 95% confidence interval of 0.76-0.85. The corresponding hazard ratio from having an (0-2 years) older sibling was 0.91 (0.86-0.96). Our results suggest that it may be possible essentially to eradicate multiple sclerosis using an Epstein-Barr virus vaccine administered before the teenage years. Getting there would require both successful replication of our study findings and, if so, elucidation of why early Epstein-Barr virus infection does not usually trigger the immune mechanisms responsible for the association between delayed Epstein-Barr virus infection and multiple sclerosis risk.

Rostgaard K ，Nielsen NM ，Melbye M ，Frisch M ，Hjalgrim H ... -  《-》

Concussion in adolescence and risk of multiple sclerosis.

To assess whether concussion in childhood or adolescence is associated with subsequent multiple sclerosis (MS) risk. Previous research suggests an association, but methodological limitations included retrospective data collection and small study populations. The national Swedish Patient Register (hospital diagnoses) and MS Register were used to identify all MS diagnoses up to 2012 among people born since 1964, when the Patient Register was established. The 7,292 patients with MS were matched individually with 10 people without MS by sex, year of birth, age/vital status at MS diagnosis, and region of residence (county), resulting in a study population of 80,212. Diagnoses of concussion and control diagnoses of broken limb bones were identified using the Patient Register from birth to age 10 years or from age 11 to 20 years. Conditional logistic regression was used to examine associations with MS. Concussion in adolescence was associated with a raised risk of MS, producing adjusted odds ratios (95% confidence intervals) of 1.22 (1.05-1.42, p = 0.008) and 2.33 (1.35-4.04, p = 0.002) for 1 diagnosis of concussion and >1 diagnosis of concussion, respectively, compared with none. No notable association with MS was observed for concussion in childhood, or broken limb bones in childhood and adolescence. Head trauma in adolescence, particularly if repeated, is associated with a raised risk of future MS, possibly due to initiation of an autoimmune process in the central nervous system. This further emphasizes the importance of protecting young people from head injuries. Ann Neurol 2017;82:554-561.

Montgomery S ，Hiyoshi A ，Burkill S ，Alfredsson L ，Bahmanyar S ，Olsson T ... -  《-》