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Column originally published May 22, 2001

Roseola Can Cause High Fever, Rash, And Febrile Convulsion In Children

Question: My sister and I had our first babies two weeks apart. Both of them are nine months of age. A month ago, her daughter developed high fever followed by a rash. Within two weeks, my son got a high fever and convulsion. Is it possible that their illnesses are somehow related? How come only my son had convulsion?


I assume, from your question, that you are very close to your sister, and both babies are playmates. If that is the case, they can be infected by the same virus, although their symptoms can be somewhat different. If I have to make a guess, I would suggest that they had roseola, a very common childhood infection.

Roseola has been well described in medical literature for almost 100 years. It was also called exanthem subitum and sixth disease. All along, physicians have suspected viral infection as the cause of this common childhood illness. Recently, a virus called Human Herpesvirus 6 (HHV6) was isolated from sick children with roseola using sophisticated viral technology.

Roseola is found all over the world. Most infections occur between 6 months to 2 years of age. Almost all three-year-olds have been infected with this virus. The most common presentation is mild upper respiratory tract infection, no different from common colds and sore throats. Some children can develop gastroenteritis. Not infrequently, the lymph glands in the head and neck can be enlarged.

Only about 20% of children infected with HHV6 will develop typical roseola symptoms. They usually have high fever (over 39.5oC) and irritability that last 3 to 7 days. Examination during this febrile phase often show a normal, but irritable child.

Typically, when the fever starts to subside, a red rash will develop over the chest, abdomen, and back. It can spread to the arms, legs, neck, and face. Each red spot measures 2 to 3 mm in diameter. The rash is usually not itchy or painful, and can last a few hours to several days. After the rash fades away, the child would make a full recovery.

Around 10% to 15% of children infected with HHV6 will develop a convulsion during high fever. There may be very little finding other than a red throat. Occasionally the soft spot on top of the head (also called anterior fontanelle) can be a little full, raising the suspicion of meningitis. HHV6 is the most common cause of febrile convulsion in children.

We don’t know why some children infected with HHV6 will develop convulsion, while others won’t. It is quite possible that some children are genetically more prone to develop febrile convulsions than others.

You may also wonder how children contract this virus infection. Most adults have been infected before three years of age. The virus stays inside the body for life. Researchers have found that the virus is constantly excreted in secretions like the saliva. Your son and his cousin likely picked up the virus from another adult (could be from one of you) or their playmates. The first sign of illness appears around 9 to 10 days after infection.

To confuse you some more, recently another virus, called Human Herpesvirus 7 (HHV7) has been found to produce a very similar illness. This may explain why, on occasion, a child seems to develop a second bout of roseola. The first infection was caused by HHV6, while the second was due to HHV7.

At the present time, there is no simple test to identify these viruses in regular laboratories. Only research facilities are capable of isolating the virus, or testing for antibody response. If a child’s symptoms look like roseola, it is safe to assume that the infection was caused by HHV6 or HHV7.

There is no treatment necessary for roseola in healthy children. All of them will recover without complication. However, those children who have weakened immune system can develop widespread infection and become seriously ill. When that happens, new anti-viral medications can be used to fight these Human Herpesviruses.

I hope this explanation will give you some insight into your son’s illness. He has a 30% chance of developing febrile convulsion in future when he gets another fever. That means he has a good chance of never having another convulsion!