Exanthem Subitum

Aetiology and epidemiology

Exanthem subitum (otherwise known as ‘sixth disease’ or ‘roseola infantum’) is caused by human herpesvirus 6 (HHV-6) and human herpesvirus 7 (HHV-7). HHV-6 is particularly widespread and nearly all children will acquire the infection early in childhood. HHV-6 infection results in a common benign illness and is a common cause of fever and febrile seizures in infants.

The incubation period for exanthem subitum is from 5-15 days.

Clinical assessment

Exanthem subitum is associated with a mild respiratory illness, 3-5 days of fever and cervical lymphadenopathy (in 30% of cases).

Some 10% of infants develop the characteristic rash, which appears as the fever disappears. It commences behind the ears, taking the form of discrete blanching macules and papules surrounded by halos. It typically lasts for 1-2 days.

Other symptoms and signs include:
1. Palpebral oedema (in 30% of cases)
2. Uvulopalatal junction ulcers
3. Erythematous papules on the soft palate also known as Nagayama’s spots (in 65% of cases)
4. Diarrhoea (in 68% of cases)
5. Cough (in 50% of cases)

Prenatal and perinatal infections are uncommon due to the presence of maternal antibodies.

Investigations

Serological testing for exanthem subitum is not necessary in the majority of cases.

Management

Human herpesvirus 6 causes a benign illness and anti-viral therapy is not needed in the majority of cases.

Children may, however, present with a febrile seizure, which may need admission for a period of observation.

The child may warrant investigation and management for a septic illness if the clinical course does not present or improve as expected.

Reactivation of the virus can occur in transplant recipients.

Complications

A number of rare central nervous system complications associated with exanthem subitum are shown in Table 1.