an exanthematous viral disease affecting babies and young children

Also known as roseola infantum, exanthem subitem, and pseudorubella. An acute disease of infants or very young children caused by HHV-6 and characterized by high fever and a skin rash.

see exanthem.

Exanthem subitum (meaning sudden rash), also referred to as roseola infantum (or rose rash of infants), sixth disease and (confusingly) baby measles, or three day fever, is a benign disease of children, generally under two years old, whose manifestations are usually limited to a transient rash ("exanthem") that occurs following a fever of about three day's duration.