The typical case of roseola occurs about ten days after exposure to the virus. A sudden fever develops, which is usually quite high—about 102 to 105 degrees Fahrenheit. Yet despite the high fever, it is not unusual for a child with roseola to look better than the fever would suggest. There are sometimes small swollen glands behind the ears or at the nape of the neck, and the eyelids may develop a subtle swelling, giving the child a sleepy appearance.
It is during the first two to five days of fever that the major complication of roseola can occur: febrile seizures. Up to 15 percent of children at this stage experience a febrile seizure, meaning a seizure that occurs in a young child (usually younger than five years) in the setting of a fever. Febrile seizures are not specific to roseola and can occur with a fever of pretty much any cause. Fortunately they don’t usually last long or leave permanent damage, but they certainly are scary for families to watch.
Since children in this first phase of roseola have only a high fever, with or without a seizure, doctors in the emergency room cannot distinguish roseola from more serious illnesses like meningitis or urinary tract infections. Invasive tests, such as blood draws and spinal taps, are necessary to get the information needed to exclude more serious causes. A quick and specific diagnostic test for roseola, similar to what is available for strep throat or influenza, would spare many, many children from painful and expensive procedures. Unfortunately, this isn’t available yet.