A mother presents to the ED because her 11 month old had fever without any other signs and symptoms for 3 days, and now “rashed out all over.” She is concerned that it is chicken pox. On physical exam you have a well appearing toddler with the following rash.

from babycenter.com

What is it?

Roseola

Roseola, AKA exanthema subitum, is a common viral illness that peaks between 7 and 13 months. The causative pathogen is HHV-6 (Human Herpes Virus 6). Almost all cases (>90%) occur before the child is two. Following 3 to 5 days of fever you get the characteristic rash. The fever can be up to 40 C and children are usually well appearing. Some can be irritable and have mild congestion or loose stools. In an “old-school” paper from 1945, Clemens noted that in a series of 80 children with roseola 98% had lymphadenopathy, 93% had red tympanic membranes and 92% were irritable.

Interestingly many small infants will have fever and bulging fontanelle early on in the illness. I have personally cared for a 5 month old with a febrile seizure. he had a subtle rash, and had a positive HHV-6 PCR. This is not a test I recommend you routinely send.

Once the fever goes away the rash will appear – hence the colloquial name “the fever that rashes.” It starts centrally on the neck and torso and spreads to the extremities and face. It is usually maculopapular and erythematous, but a few children will have a vesicular eruption. It usually lasts for <48 hours though some cases it may only be present for a few hours.

As long as the diagnosis is correct treatment is supportive. Most kids don’t itch, and since the fever is generally gone antipyretics aren’t necessary. Reassurance is key. Once the fever is gone send them back to daycare.