Roseola infantum (Exanthem subitum)

Overview

•Cause: human herpesvirus 6 (HHV-6), less commonly HHV-7

•Age: peak 6 months to 2 years

Presentation

•Phase 1: high fever (up to 40°C) for 3-5 days - child appears unwell

•Phase 2: fever resolves, then blanching rose-pink macular rash appears on trunk spreading to neck/limbs

•Nagayama's spots - red papules on soft palate (pathognomonic during febrile phase)

🎯
The rash appears AS the fever breaks - not alongside it. High fever for days, then rash as temperature normalises = roseola until proven otherwise.

Investigations

•Clinical diagnosis - no investigations required in a well immunocompetent child

🥈 Second-line

•HHV-6 serology or PCR - atypical presentations, immunocompromised, or suspected encephalitis

Differential Diagnosis

Key childhood exanthems compared
FeatureRoseolaHand, foot & mouthFifth disease (slapped cheek)
CauseHHV-6Coxsackievirus / EnterovirusParvovirus B19
Age6 months - 2 yearsUnder 10 years5-15 years
Rash timingAfter fever resolvesWith feverAfter mild prodrome
Rash distributionTrunk first, then spreadsHands, feet, mouth, buttocksSlapped cheeks, lacy trunk rash
Oral involvementNagayama's spots (soft palate)Mouth ulcers/vesiclesNone typical

Feature	Roseola	Hand, foot & mouth	Fifth disease (slapped cheek)
Cause	HHV-6	Coxsackievirus / Enterovirus	Parvovirus B19
Age	6 months - 2 years	Under 10 years	5-15 years
Rash timing	After fever resolves	With fever	After mild prodrome
Rash distribution	Trunk first, then spreads	Hands, feet, mouth, buttocks	Slapped cheeks, lacy trunk rash
Oral involvement	Nagayama's spots (soft palate)	Mouth ulcers/vesicles	None typical

Management

🥇 First-line

•paracetamol 15 mg/kg every 4-6 hours (max 4 doses/24 h) - antipyretic

•Alternative: ibuprofen 5-10 mg/kg every 6-8 hours - avoid under 3 months

•Adequate oral hydration; exclude from nursery until well

🥈 Second-line

•aciclovir or ganciclovir - only for HHV-6 encephalitis or severe immunocompromised disease; not used in immunocompetent children

Complications

•Febrile convulsions - most common complication; roseola is a leading cause of first febrile convulsion due to the rapid temperature spike

•HHV-6 encephalitis - rare in immunocompetent; more significant post-transplant (limbic encephalitis)

⚠️
Safety-net parents about febrile convulsions: place child on side, time the seizure, call 999 if >5 minutes or first seizure. A single brief self-terminating febrile convulsion does not require hospital admission if child recovers fully.

Prognosis

•Excellent - self-limiting, resolves within 7-10 days; no long-term sequelae in immunocompetent children