Roseola (Exanthem Subitum, Sixth Disease)

BASICS

Definition: Acute viral infection of infancy/early childhood, most commonly caused by human herpesvirus 6 (HHV-6); less often by HHV-7.
Classic presentation: High fever for 3–5 days, abrupt resolution of fever, then appearance of rose-pink macular/papular rash (exanthem) as fever subsides.
Transmission: Contact with saliva or respiratory droplets.
Incubation: 9–10 days.
Other names: Roseola infantum, exanthem subitum, sixth disease, 3-day fever.

Age: Peak 6–9 months; almost all infected by 2–3 years (HHV-6), or by 10 years (HHV-7).
Prevalence: Nearly universal infection by age 3.
Incidence: Accounts for 20% of ED visits for febrile illness in children 6–8 months old.
Gender: No sex predilection.
Seasonality: None.

Agents: HHV-6 (esp. HHV-6B), HHV-7.
Transmission: Respiratory/salivary droplets, rarely vertical (transplacental, chromosomal integration).
Course: Primary infection → viremia (2 days before fever until rash), then lifelong latent infection.
Shedding: 80–90% intermittently shed virus in saliva.

Fever: Abrupt, high (102–104°F, 39–40°C) for 3–5 days; child may be irritable.
Rash: Appears as fever resolves, starts on trunk, spreads peripherally (neck, extremities, face).
Other: Diarrhea, mild URI symptoms, rhinorrhea. Febrile seizure in ~13% of cases.

Rash: Rose-pink macules/papules, blanching, first on trunk, fades within 2 days, ~20% US cases.
Other: Tympanic/pharyngeal/conjunctival erythema, Nagayama spots (palate ulcers), cervical lymphadenopathy, periorbital edema.

Enterovirus, adenovirus, Epstein-Barr virus, parvovirus B19 (fifth disease), rubella, scarlet fever, drug eruption, measles.

Diagnosis is clinical; labs not usually needed.
PCR or serology (IgM, IgG) only in severe, atypical, or immunocompromised cases.
Lab findings (if obtained): leukopenia, thrombocytopenia, elevated transaminases.
Rule out UTI or pneumonia in children with prolonged fever.

Supportive only: Antipyretics, hydration.
No antivirals in immunocompetent hosts.
Antivirals (ganciclovir, foscarnet) for select immunocompromised, severe encephalitis.

Prognosis: Benign, self-limited, full recovery in immunocompetent children.
No exclusion needed from daycare/school after fever resolves and child is well.
Febrile seizures: Not usually recurrent after roseola episode.

Febrile seizures: ~13%, account for 1/3 of first seizures in <2 yrs.
Reactivation: Encephalitis, drug reaction with eosinophilia and systemic symptoms (immunocompromised).
Rare: Meningoencephalitis, association with pityriasis rosea, possible link to PML.

Suspect in infant/young child with high fever, then trunk rash as fever abates.
Classic macular rash appears as fever resolves, spreads to extremities/face in 20%.
Clinical diagnosis—labs rarely required.
Symptomatic care only—antivirals not needed in healthy children.
Consider prophylaxis (e.g., ganciclovir) in transplant patients under immunosuppression.