A prospective study of recurrent febrile seizures.

BACKGROUND: Febrile seizures occur in about 2 to 4 percent of all children, approximately one third of whom will have recurrent febrile seizures. Little is known about predictors of recurrence.

METHODS: In this prospective study, we identified 347 children (1 month to 10 years of age) who presented with a first febrile seizure at one of four pediatric emergency departments. Information about these children was collected from medical records and interviews with the parents, and the children were followed for a median of 20 months to ascertain whether febrile seizures recurred.

RESULTS: Recurrent febrile seizures occurred in 94 of the 347 children (27 percent) with a cumulative risk of 25 percent at one year and 30 percent at two years. The duration of fever before the initial seizure was associated with the risk of recurrence at one year: for fever lasting less than 1 hour, the risk of recurrence was 44 percent; for fever lasting 1 to 24 hours, 23 percent; and for fever lasting more than 24 hours, 13 percent (P less than 0.001). With each degree of increase in temperature (in degrees Fahrenheit), from 101 degrees F (38.3 degrees C) to greater than or equal to 105 degrees F (40.6 degrees C), the risk of recurrence at one year declined, from 35 percent to 30, 26, 20, and 13 percent (P for trend = 0.024). An age of less than 18 months and a family history of febrile seizures were also associated with an increased risk of recurrence. A family history of epilepsy, complex febrile seizures, and neurodevelopmental abnormalities did not increase the risk of recurrent febrile seizures.

CONCLUSIONS: A shorter duration of fever before the initial febrile seizure and a lower temperature are associated with an increased risk of recurrence in children who have febrile seizures.