Antibody reactivity was determined in 147 untreated CIS patients and 50 demographically matched controls recruited from the same geographical area (Barcelona, Spain), as described in Methods. IgG responses towards EBNA1, EBV-encoded viral VCA and pooled EA as well towards lysates of other viruses previously associated with MS (HHV6, measles, HCMV) were quantified using commercially available ELISA kits. The percentage of individuals showing a positive response towards each antigen preparation. i.e. seroprevalence, is given below the diagrams. The non-parametric Mann Whitney U test was used to compare frequencies between CIS patients and healthy donors (HD).