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Introduction

Roseola infantum (exanthema subitum or sixth disease) is a common childhood viral exanthem caused primarily by human herpesvirus 6 (HHV-6).  It presents with a high fever for several days, followed by abrupt defervescence and the development of a maculopapular rash.

Pathophysiology and risk factors

HHV-6 infects most children by age 2 years and is most likely transmitted through infected secretions of asymptomatic close contacts (eg, via saliva from mother to infant).  Following transmission, the mean incubation period is approximately 9-10 days.  HHV-6 replicates within CD4+ T cells, causing immune dysfunction and cytokine production that manifests as high fever.  The cause of the rash is unknown but may be related to antibody-antigen interaction after the initial febrile phase.

After initial infection, HHV-6 remains latent in the body, contributing to asymptomatic lifelong shedding and a high prevalence of infection among infants and young children with no known exposure.  There are no risk factors for roseola infantum, but infection is most common in children age <2.

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