The influence of febrile episodes, a risk factor for recurrence of febrile seizures, and outcome in 180 children followed prospectively after their first febrile seizure, were studied at the University of Oulu, Finland. In a 2-year follow-up of 156 patients, each febrile episode increased the risk of febrile seizure recurrence by 18%. Of 38 patients with recurrences, 27 had single and 11 had multiple recurrences. EEG spikes or spike-and-wave abnormalities occurred in 14% of 35 children with recurrences and in 9% of 121 without recurrences. Each degree of temperature (Celsius) increase during subsequent infections almost doubled the risk of seizure recurrence. Age, sex, or family history of febrile seizures or epilepsy were not risk factors for febrile seizure recurrence. 
COMMENT. This study corroborates previous reports that the height of a fever is the most important determinant of a febrile convulsion, and treatment aimed at prevention of infection and a rise in temperature to the “threshold convulsive level“ should decrease the risk of febrile seizure recurrence (Millichap JG. Febrile Convulsions. New York, Macmillan, 1968). Rantala and colleagues show that the frequency of febrile episodes after the initial seizure is a risk factor for recurrence of febrile seizures. Children with recurrences have higher temperatures than those without, supporting the theory of a febrile seizure threshold dependent on the height of the temperature.
Prediction of febrile seizures in siblings was studied prospectively in 129 children with FC at Sophia Children’s Hospital, Rotterdam, The Netherlands . The risk of FS in siblings was 10%, more than twice the population risk (4%). The overall risk of FS in first degree relatives of FS probands was 7%. The risk was increased to 16% in siblings with recurrent FS and 25% in siblings with an affected parent. A polygenic mode of inheritance seemed likely. A prediction model based on three risk factors was developed. The risk factors are: 1) FS in the parents; 2) age at first FS of proband under 1 year; and 3) FS recurrence in the proband. The risk of FS in siblings of FS probands may increase to 46% with 2 or 3 risk factors present and it falls to less than 10% if a sibling is unaffected up to 3 years of age.