THURSDAY, Aug. 7 (HealthDay News) -- Even in high-risk children, death from febrile (fever-linked) seizures is rare, say Danish researchers who analyzed data on 1.6 million children.

Febrile seizure, a generalized convulsion caused by increased body temperature, affects 2 percent to 5 percent of children under age 5. About one-third of affected children have more than one seizure episode. Many parents fear their child is dying during a febrile seizure and are worried death may occur during subsequent seizures, according to background information in a news release about the study.

This study included almost 1,676,000 children born in Denmark between 1977 and 2004, who were followed from three months of age until death, emigration or Aug. 31, 2005. Among the children, there were a total of 8,172 deaths, including 232 deaths among the 55,215 children with a history of febrile seizure.

Overall, 132 per 100,000 children died within two years of a febrile seizure compared with 67 per 100,000 children without a history of the condition.

The duration of the fever episode seemed to matter, however. The death rate for children with simple febrile seizures (lasting less than 15 minutes and none recurring within 24 hours) was similar to that of children in the general population. In contrast, the death rate for children with complex febrile seizures (lasting longer than 15 minutes or recurring within 24 hours) was twice as high in the two years following the seizure than in the general population.

But the researchers emphasized that the overall risk of death among children with febrile seizures is small -- 2 deaths per 1,500 children, compared with 1 death per 1,500 children in the general population.

"Children with simple febrile seizures had a risk of death similar to the background population, whereas those with complex febrile seizures, febrile seizures triggered by a temperature below 39 degrees C, and febrile seizures occurring before 12 months of age had a twofold higher mortality lasting for about two years. The excess mortality was at least partly due to pre-existing neurological abnormalities and subsequent epilepsy ... Parents should be reassured that death after febrile seizures is very rare, even in high-risk children," the researchers concluded.

The study was published in this week's issue of The Lancet.

The U.S. National Institute of Neurological Disorders and Stroke has more about febrile seizures.