Multiple sclerosis and age at infection with common viruses

Increased risk of multiple sclerosis has been reported among individuals wi th a history of measles and other common childhood diseases during adolesce nce, infectious mononucleosis, or exposure to the canine distemper virus. W e investigated these associations in a case control study nested within the Nurses' Health Study (121,700 women traced since 1976) and the Nurses' Hea lth Study II (116,671 women traced since 1989). Age at diagnosis of common viral diseases and birth order were obtained through a questionnaire. Our r esults include 301 cases with multiple sclerosis and their (up to six) matc hed controls. Except for infectious mononucleosis, which was a moderate ris k factor (odds ratio = 2.1, 95% confidence interval = 1,5-2.9), we found li ttle association between history of common viral diseases or exposure to ca nine distemper virus and risk of multiple sclerosis. We did find a relation between mumps after 15 years of age (odds ratio = 2.3, 95% confidence inte rval = 1.2-4.3) or measles after age 15 years of age (odds ratio = 2.8, 95% confidence interval = 0.8-9.1) and multiple sclerosis. Birth order was not materially related to multiple sclerosis. Our findings support the hypothe sis that individuals who suffered from infectious mononucleosis, a marker o f late infection with the Epstein-Barr virus, have an increased risk of mul tiple sclerosis. Late infection with other common viruses may also be assoc iated with increased risk.