By the eighth day of illness, antibody activity peaks and results in resolution of the viremia. Children with the cell-free virus also have been noted. This likely represents a greater magnitude of viral dissemination because these children have more severe clinical manifestations. Eighty-six percent of children have acquired HHV6 antibodies by age 1 year. By age 4 years, almost all children are seropositive.
Roseola appears to peak in spring and fall.
The disease is more prevalent among younger infants in Japan than in the US or Europe. Roseola is usually a self-limited illness with no sequelae. Encephalitis, fulminant hepatitis, hemophagocytic syndrome, and disseminated infection with HHV6 are extremely rare manifestations. Most cases present within the first 2 years of life, with peak occurrence in infants aged 7-13 months. Lesions are characteristically discrete, rarely coalesce, and fade with blanching of the skin surface.