Background
Roseola infantum is the sixth of the traditional exanthems of childhood. The condition is an acute benign disease of childhood classically characterized by a history of a prodromal febrile illness lasting approximately 3 days, followed by defervescence and the appearance of a faint pink maculopapular rash.
Since identification of the etiologic agent human herpesvirus type 6 (HHV-6), infection has been documented without the characteristic fever or rash. The virus may present as an acute 3-7 day febrile illness (characteristically >39.5 º C) associated with respiratory or gastrointestinal symptomatology. In one prospective cohort, 93% of newly acquired infections were symptomatic, with fever, fussiness, diarrhea, and rash as the most distinguishing features. [1]
Newly recognized clinical manifestations of HHV-6 infection include hepatitis, encephalitis, myocarditis, hemophagocytic syndrome, and an adult mononucleosislike illness. The virus persists and may reactivate, primarily in immunocompromised hosts. Reactivation manifestations may present as fever, rash, pneumonia, hepatitis, bone marrow suppression, and encephalitis. [2] The full spectrum of clinical manifestations of HHV-6 has not been elucidated.
Pathophysiology
Respiratory secretions of asymptomatic individuals likely transmit the virus. The child is most likely to spread the infection during the febrile and viremic phase of the illness.
Cell-associated viremia has been noted, usually on the third day of illness and immediately before rash appearance. By the eighth day of illness, antibody activity peaks and results in resolution of the viremia.
Children with the cell-free virus also have been noted. This likely represents a greater magnitude of viral dissemination because these children have more severe clinical manifestations.
Epidemiology
Frequency
United States
Approximately 12-30% of children have clinical manifestations consistent with roseola. Eighty-six percent of children have acquired HHV-6 antibodies by age 1 year. By age 4 years, almost all children are seropositive. Roseola appears to peak in spring and fall.
International
A relationship seems to exist among prevalence, geographic location, and ethnicity. The prevalence of roseola is 92% in Ecuador, 60% in Japan, 20% in Morocco, and 49-76% in Malaysia. The disease is more prevalent among younger infants in Japan than in the United States or Europe.
Mortality/Morbidity
Roseola is usually a self-limited illness with no sequelae.
The major morbidity associated with roseola is seizures (6-15%) during the febrile phase of the illness.
Encephalitis, fulminant hepatitis, hemophagocytic syndrome, and disseminated infection with HHV-6 are extremely rare manifestations in healthy hosts. Immunosuppression secondary to transplantation may result in viral replication and reactivation. While HHV-6 is commonly detected post transplantation, it is generally asymptomatic. However, it has been implicated in encephalitis, hepatitis, bone marrow suppression, and pneumonitis in a minority of cases. [2]
Sex
No predilection for roseola infantum exists.
Age
Most cases present within the first 2 years of life, with peak occurrence in infants aged 9-21 months.
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Discrete rose-pink macules/maculopapules characteristic of roseola infantum.
