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

Key Points Question Is diagnosis of infectious mononucleosis (IM) in childhood or adolescence associated with subsequent development of multiple sclerosis (MS)? Findings In this population–based cohort study of 2 492 980 individuals in Sweden, IM in childhood and adolescence was associated with an increased risk of a subsequent MS diagnosis that remained significant after controlling for measured and unmeasured shared familial factors. Meaning These findings suggest that IM in childhood and particularly adolescence is a risk factor for a subsequent MS diagnosis, independent of shared familial factors, making it less likely that greater susceptibility to infection is the explanation.