An acute, short-lived, viral disease of infants and young children characterized by a high fever at onset that drops to normal after 3-4 days and the concomitant appearance of a macular or maculopapular rash that appears first on the trunk and then spreads to other areas. It is the sixth of the classical exanthematous diseases and is caused by HHV-6; (HERPESVIRUS 6, HUMAN). (From Dorland, 27th ed)