Human herpesvirus-6 infection (exanthem subitum) without rash.

Two patients with a three-day febrile episode in whom exanthem subitum was expected showed no appearance of skin eruption after subsidence of the fever. Virus was isolated from peripheral blood mononuclear cells in the acute stage, which was identified by the cytopathic effects of infected cells and the specific immunofluorescent staining of the cells with convalescent sera from exanthem subitum, but the virus could not be isolated from those in the convalescent stage. The morphology of the virus was similar to herpes group virus. There were seroconversions against representative strain of the causative agent of exanthem subitum in the two patients. The results indicated the presence of atypical clinical course of exanthem subitum.