Season of infectious mononucleosis and risk of multiple sclerosis at different latitudes;the EnvIMS Study

Abstract

Background:

Seasonal fluctuations in solar radiation and vitamin D levels could modulate the immune response against Epstein-Barr virus (EBV) infection and influence the subsequent risk of multiple sclerosis (MS).

Methods:

Altogether 1660 MS patients and 3050 controls from Norway and Italy participating in the multinational case-control study of Environmental Factors In Multiple Sclerosis (EnvIMS) reported season of past infectious mononucleosis (IM).

Results:

IM was generally reported more frequently in Norway (p=0.002), but was associated with MS to a similar degree in Norway (odds ratio (OR) 2.12, 95% confidence interval (CI) 1.64–2.73) and Italy (OR 1.72, 95% CI 1.17–2.52). For all participants, there was a higher reported frequency of IM during spring compared to fall (p<0.0005). Stratified by season of IM, the ORs for MS were 1.58 in spring (95% CI 1.08–2.31), 2.26 in summer (95% CI 1.46–3.51), 2.86 in fall (95% CI 1.69–4.85) and 2.30 in winter (95% CI 1.45–3.66).

Conclusions:

IM is associated with MS independently of season, and the association is not stronger for IM during spring, when vitamin D levels reach nadir. The distribution of IM may point towards a correlation with solar radiation or other factors with a similar latitudinal and seasonal variation.