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Roseola Infantum
Judith D. Laval, MD
Roseola infantum (exanthem subitum, sixth disease) is caused by human herpes virus 6 (HHV-6), which is similar to cytomegalovirus. Two genotypes of HHV-6 (type A and type B) have been distinguished. As with other herpes viruses, HHV-6 shows persistent and intermittent or chronic shedding in the normal population, making the unusually early infection of children (seroconversion in the first year of life in up to 80% of all children) understandable. It is probably latent in salivary glands and blood. Virus may infect infants through the saliva mainly from mother to child. A severe, infectious mononucleosis-like syndrome in adults may be caused by a primary infection with HHV-6. HHV-6 has also been implicated in idiopathic pneumonitis in immunocompromised hosts.
Most cases are asymptomatic or present with fever of unknown origin and occur without a rash. The disease is sporadic, and the majority of cases occur between the ages of 6 months and 4 years. HHV-6 antibody is present in 90% to 100% of the population over age 2. The development of high fever, as is seen in roseola, is worrisome, but the onset of the characteristic rash is reassuring. In infants and young children HHV-6 is a major cause of visits to the emergency department, febrile seizures, and hospitalizations.
The incubation period of roseola infantum is 12 days, with a range of 5 to 15 days.
There is a sudden onset of high fever of 103° to 106° F with few or minor symptoms. Most children appear inappropriately well for the degree of temperature elevation, but they may experience slight anorexia or one or two episodes of vomiting, running nose, cough, and hepatomegaly. Seizures (but more frequently general cerebral irritability) may occur before the eruptive phase. Most recover without sequelae. Cases of encephalitis/encephalopathy with abnormal electroencephalograms and cerebral computed tomograms have been reported; epilepsy developed in one case and another died. HHV-6 DNA has been detected in the cerebrospinal fluid (CSF); this suggests that HHV-6 may invade the brain during the acute phase. HHV-6 infection should be suspected in infants with febrile convulsions, even those without the exanthem. Mild-to-moderate lymphadenopathy, usually in the occipital regions, begins at the onset of the febrile period and persists until after the eruption has subsided.
The rash begins as the fever subsides. The term exanthem subitum indicates the sudden "surprise" of the blossoming rash after the fall of the fever. Numerous pale pink, almond-shaped macules appear on the trunk and neck, become confluent, and then fade in a few hours to 2 days without scaling or pigmentation. The exanthem may resemble rubella or measles, but the pattern of development, distribution, and associated symptoms of these other exanthematous diseases are different.
Leukocytosis develops at the onset of fever, but leukopenia with a granulocytopenia and relative lymphocytosis appears as the temperature increases and persists until the eruption fades. Seroconversion during the convalescent phase can be detected with immunofluorescence or enzyme immunoassays.
Control temperature with acetaminophen and provide reassurance.