The consistency of Epstein-Barr nuclear antigen-1 (EBNA-1) seropositivity with multiple sclerosis (MS) across racial/ethnic groups and between studies points to a strong biological link between Epstein-Barr virus (EBV) infection and MS risk, a recent study found. The association between past cytomegalovirus (CMV) infection and MS risk supports the broader hygiene hypothesis, but the inconsistency of this association across racial/ethnic groups implies non-causal associations. Incident cases of MS or its precursor, clinically isolated syndrome (CIS), and matched controls (blacks, 111 cases/128 controls; Hispanics, 173/187; whites, 235/256) were recruited from the membership of Kaiser Permanente Southern California. They found:

• EBNA-1 seropositivity was independently associated with an increased odds of MS/CIS in all 3 racial/ethnic groups.
• In contrast, CMV seropositivity was associated with a lower risk of MS/CIS in Hispanics but not in blacks or whites.
• Being born in a low/middle-income country was associated with a lower risk of MS in Hispanics but not after accounting for EBNA-1 seropositivity.
• Accounting for breastfeeding did not diminish the association between CMV and MS in Hispanics.