Distribution of antibodies to a causative agent of exanthem subitum (human herpesvirus-6) in healthy individuals.

The transfer of IgG antibodies to a causative agent of exanthem subitum (human herpesvirus-6) from mother to infant was examined with an indirect immunofluorescence assay. Of 20 mothers, 85% had the antibody more than 1:10, and the significantly higher level of the antibody was found in the cord blood with a positive rate of 95%. A mean ratio of cord blood to maternal antibody titer was 1.63. A total of 301 sera from healthy individuals was examined for the age-specific prevalence of antibody to the virus. In the first 2 months of life, 87% of infants had the antibody; the positive rate and the level of antibody decreased during the first 6 months of life with the lowest positive rate of 6% at 4 to 5 months of age. After 6 months of age, they increased gradually and reached the highest level at 1 year of age with the positive rate of 86%. From 2 years of age, the prevalence of the antibody was almost stable (69% to 76%) and similar to those in adolescents and adults.