(Exanthem Subitum; Pseudorubella)
Roseola infantum is an infection of infants or very young children caused by human herpesvirus 6B (HHV-6B) or, less commonly, HHV-7. The infection causes high fever and a rubelliform eruption that occurs during or after defervescence, but localizing symptoms or signs are absent. Diagnosis is clinical, and treatment is symptomatic.
Roseola infantum is the most well-described illness to result from HHV-6. HHV-6B may also cause CNS disease in immunocompromised patients (eg, hematopoietic stem cell transplant recipients). Roseola infantum occurs most often in the spring and fall. Minor local epidemics have been reported.
The incubation period is about 5 to 15 days. Fever of 39.5 to 40.5° C begins abruptly and persists 3 to 5 days without any localizing symptoms or signs. Despite the high fever, the child is usually alert and active, although febrile seizures may occur (see Febrile Seizures). Cervical and posterior auricular lymphadenopathy often develops. Encephalitis or hepatitis occurs rarely.
The fever usually falls rapidly on the 4th day, and when the fall occurs, a macular or maculopapular exanthem usually appears prominently on the chest and abdomen and, to a lesser extent, on the face and extremities; it lasts for a few hours to 2 days and may be unnoticed in mild cases. In 70% of HHV-6 infections, the classic exanthem does not occur.