Role of human herpesvirus 6 infection in infants with exanthema subitum.

Twenty-two infants with exanthema subitum and their mothers were studied for human herpesvirus 6 (HHV-6) infection. HHV-6 was isolated from 13 of the 22 infants, in 5 infants by cultivation of their peripheral blood mononuclear cells and in the other 8 infants by cocultivation of their mononuclear cells with those from newborn cord blood. Of the 22 infants 19 showed a 4-fold or greater rise in HHV-6 antibody titers between the acute and convalescent stages of the disease. These findings support the contention that HHV-6 causes exanthema subitum. Attempts at isolation of HHV-6 from the saliva and peripheral blood mononuclear cells of the mothers of 14 of the 22 infants were unsuccessful. Serum samples from 22 mothers were all reactive to HHV-6 antigens, as evidenced by immunofluorescence and radioimmunoprecipitation analyses.