Exanthema Subitum

Exanthema subitum (meaning sudden rash), also referred to as roseola infantum (or rose rash of infants), sixth disease (as the sixth rash-causing childhood disease), and (confusingly) baby measles, or three-day fever, is a disease of children, generally under two years old, although it has been known to occur in eighteen year olds, whose manifestations are usually limited to a transient rash ("exanthem") that occurs following a fever of about three day's duration.

It is frequently called roseola, although this term could be applied to any rose-colored rash.

It is caused by two human herpesviruses, HHV-6 (Human herpesvirus 6) and HHV-7, which are sometimes referred to collectively as Roseolovirus. There are two variants of HHV-6 (HHV-6a and HHV-6b) and studies in the US, Europe, Dubai and Japan have shown that exanthema subitum is caused by HHV-6b. This form of HHV-6 infects over 90% of infants by age 2. Research has shown that babies can be congenitally infected with HHV-6 via vertical transmission. This has been shown to occur in 1% of births in the United States.