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Roseola infantum
A 13-month-old girl has had a high fever of 39.5 degrees Celsius for three days, during which she remained alert and playful between temperature spikes. The fever then settled abruptly, and a few hours later a fine rose-pink macular rash appeared on the trunk and spread to the neck. She is now well. What is the diagnosis?
- correctA. Roseola infantum
- B. Rubella
- C. Scarlet fever
- D. Measles
Explanation
Key fact
In roseola the rash appears as the fever disappears. In measles the rash appears while the fever is at its height.
Roseola infantum. Three days of high fever in a well-looking infant, then defervescence, then the rash.
Why
It is caused by human herpesvirus 6, occasionally 7.
It affects infants between about 6 months and 2 years.
The fever is high but the child looks surprisingly well between spikes.
The fever stops abruptly, and only then does the rash appear.
The rash is fine, rose-pink, on the trunk first, and fades within a day or two.
It is the classic cause of a febrile convulsion in this age group.
Fever and rash: which comes first
Why not the others
- B. Rubella — gives a mild fever with suboccipital and posterior auricular lymphadenopathy and a rash that appears with the fever, not after it.
- C. Scarlet fever — follows streptococcal pharyngitis with a sandpaper rash, circumoral pallor and a strawberry tongue, and the child has a sore throat.
- D. Measles — has a prodrome of cough, coryza and conjunctivitis with Koplik spots, and the rash appears at the height of the fever in a miserable child, starting behind the ears.
Remember
Fever falls, rash appears - roseola. It is the only common exanthem that works that way round.
Go deeper
It is a leading cause of febrile seizures between 6 months and 3 years, and of unnecessary antibiotic prescription and septic screens.
Treatment is supportive; the illness is self-limiting.
The virus establishes latency and can reactivate in the immunosuppressed, causing encephalitis and marrow suppression.
Ghai Essential Pediatrics, 10th ed. (CBS Publishers, 2025); Nelson Textbook of Pediatrics, 22nd ed. (Elsevier, 2024).