FS have a peak incidence at 18 months of age and are most
common between 6 months and 5 years [10]. Most FS are simple with
approximately 20-30% being complex [13]. The distribution of a first
FS duration can be described using a two population model, one with
short seizure duration and the other with long seizure duration, with
the cut-off at approximately 10 minutes [12]. Approximately 5% of FS
will last ≥30 minutes [14]. No correlation has been identified between
duration of the first FS and duration of the second FS [12]. Although,
it has been observed that a recurrent febrile seizure is more likely to be
prolonged if the initial FS was prolonged [13].
By definition, a febrile illness is required for a child to have a FS.
Children with FS have higher temperatures with illness compared to
febrile controls [15]. The rapid onset of fever was previously thought
to be precipitating factor of FS, but this is no longer thought to be true
[16]. Gender predominance of FS has also been studied. There are
studies that conclude a higher incidence of FS in males [17] and others
showed no significant difference based on gender [18].
FS occur in the setting of a febrile illness, which could cause seasonal
variation. In Japan a study of FS showed two peaks of incidence,
November to January and June to August, which correspond to peaks
of viral upper respiratory infections and gastrointestinal infections
respectively [19]. A study performed in Italy, which looked at 188 first
FS, found that there is a significant increase in FS from 6 PM to 11:59
PM and a seasonal peak in January [20]. There have been multiple
studies have supported the conclusion that FS have a peak in the winter
and end of the summer [21-23]. Influenza A has been found to have a
significant relationship with recurrence of FS [24]. Although it has been
suggested that FS are more likely to occur with respiratory illnesses
compared to viral gastrointestinal illness [15,25], any febrile illness