Roseola infantum (exanthem subitum, sixth disease)
Overview
Roseola infantum is a common, usually self‑limited viral illness of infancy caused most often by primary infection with human herpesvirus‑6B (HHV‑6B) and less commonly HHV‑7. It classically affects previously well children aged about 6 months to 3 years, with many infections asymptomatic or very mild. Household spread via saliva from asymptomatic carriers is typical. Incubation is approximately 10 days.
Typical clinical course
- Presentation: abrupt high fever (often 38.5-40°C) lasting 2-5 days.
- Associated symptoms: frequently mild upper respiratory symptoms (rhinorrhoea, sore throat, cough) and sometimes diarrhoea.
- Rash timing: fever usually resolves quickly; within 24-48 hours of defervescence a blanching, rose‑pink maculopapular rash appears.
- Rash distribution and duration: classically starts on the trunk and spreads to the neck, face and proximal limbs; generally non‑pruritic and short‑lived (hours to a few days).
- Mucosal sign: Nagayama spots (small erythematous papules on the soft palate/uvula) are commonly seen.
- Complication: febrile seizures occur in a minority of symptomatic children (commonly quoted ~10-15%).
Pathophysiology and complications
- Primary HHV‑6/7 infection produces viraemia and high fever; the rash typically appears as the fever subsides and reflects the host immune response.
- In immunocompetent children the illness is self‑limited and recovery is complete.
- In immunocompromised patients viral reactivation can cause severe disease (including encephalitis); specialist assessment with targeted testing and therapy is required.