The mother of a 7 month male brought her child to the office one day ago and the child had a temperature of 39.4 and a negative physical examination. She calls today and states that the child has a rash on the trunk and the fever is gone. What is the most likely diagnosis?

Roseola is a common pediatric disease that is caused by the human herpes virus-6. The virus was initially discovered in the lymphocytes in immunoincompetent adults and shortly thereafter was discovered to be the etiologic agent in roseola. In a large prospective study, HHV-6 has been found responsible for approximately 20%of emergency department visits in children less than 2 years of age for evaluation of fever as diagnosed by seroconversion and recovery of virus from the blood.

Epidemiology

1. Most newborns receive protective antibody transplacentally and this lasts for about 3 months. By 2 years of age, 90% of children will be infected by the virus and show an antibody response. The virus is not transmitted through breast milk. Not all infections will be associated with a recognizable clinical disease. The peak incidence of infection is between 6-12 months and this correlates with the high incidence of roseola. 
2. Most likely spread by oral route 

1. Roseola
2. high fever without rash that may last from 1-21 days. Often leads to workup for sepsis and bacteremia. 
3. URI
4. Pharyngitis
5. Red tympanic membrane
6. GI symptoms.
7. Seizures associated with fever although usually no pleocytosis. In a large study in Rochester, New York, 1/3 of febrile seizures were associated with HHV-6
8. Encephalopathy may be associated with +PCR
9. Case reports of ITP hepatitis, mono-like illnesses, and intussusception.

1. Isolation of virus from the blood and presence of antibody.

1. Rubella- usually not asssociated with high fever
2. Rubeola-sick appearing, cough, conjunctivitis, coryza.
3. Enteroviral infections-often have oral lesions
4. Drug reaction
5. Pneumococcal bacteremia
6. Mononucleosis-may have pharygitis and significant adenopathy

1. Majority of cases are due to HHV-6 but some cases may be enteroviruses. >3 months and peaks 6-12 months. Rare after 2 years of age. 
2. abrupt onset of fever often associated with seizure. 
3. Child usually looks reasonably well and physical exam is normal
4. As the temperature returns to normal, the infant breaks out with rash initially on the trunk and then spreads to the neck and extremities. Usually not pruritic and may last several hours to several days. 
5. Diagnosis by exclusion of other causes of high fever. 
6. Treatment is supportive.

1. Hall, Caroline Breese. Herpesvirus VI: New light on an old childhood exanthem. Contemporary Pediatrics. January, 1996
2. Hall, Caroline Breese. et. al. Human Herpesvirus-6 Infection in Children. A Prospective Study of Complications and Reactivation. NEJM. August 18, 1994
3. Prober C. Sixth Disease and the Ubiquity of Human Herpesviruses. NEJM Feb 24, 2005
4. Zerr D. A Population-Based Study of Primary Human Herpesvirus 6 Infection. NEJM Feb 24, 2005