Definition and epidemiology
A febrile seizure is a seizure accompanied by fever (temperature ≥38°C), without CNS infection or acute electrolyte derangement, in a child 6 through 60 months of age with no history of an afebrile seizure. It is the most common seizure disorder of childhood, affecting 2–5% of children. Most occur on the first day of a febrile illness, frequently as the temperature rises; common triggers include viral infections (notably HHV-6) and, temporally, certain vaccinations. Genetic predisposition is well recognised, with frequent family history.
Clinical features
Febrile seizures are categorised by their characteristics:
- Simple: generalised (usually tonic-clonic), lasting <15 minutes, and not recurring within 24 hours. This is the large majority and carries an excellent prognosis.
- Complex: any of — focal onset/features, duration ≥15 minutes, or recurrence within 24 hours (or within the same febrile illness).
- Febrile status epilepticus: a febrile seizure lasting ≥30 minutes.
A brief post-ictal drowsiness is expected; persistent altered consciousness, focal deficit, or meningism is not and demands investigation.
Diagnostic criteria
The diagnosis is clinical, resting on the age window, presence of fever, exclusion of CNS infection/metabolic cause, and no prior afebrile seizure. For a simple febrile seizure in a well-appearing child, the AAP advises that routine blood tests, EEG, and neuroimaging are not indicated — investigations should be directed at identifying the source of fever. Lumbar puncture should be performed when there are signs or symptoms of meningitis, and considered in infants 6–12 months who are under- or un-immunised against Hib/pneumococcus, or in children pretreated with antibiotics that may mask meningitis. Complex febrile seizures warrant individualised evaluation and are more likely to prompt neuroimaging/EEG.
See the full criteria: Febrile Seizure
Red flags
- Any sign of meningitis/encephalitis — bulging fontanelle, neck stiffness, petechiae, persistent altered mental status
- Age <6 months or >5 years (consider alternative diagnoses; this lies outside the febrile-seizure definition)
- Complex features, focal deficit, or failure to return to baseline
- Prolonged seizure / febrile status epilepticus
- Ill or toxic appearance, or an unclear fever source
Management overview
Acute management mirrors any seizure: position safely, support airway, and treat ongoing convulsions lasting >5 minutes with a benzodiazepine (e.g. IV/IO lorazepam, or buccal/intranasal midazolam or rectal diazepam where IV access is delayed). Identify and treat the underlying febrile illness. Counsel families that simple febrile seizures are benign, do not cause brain damage, and carry only a small increase in later epilepsy risk; recurrence occurs in roughly a third, higher with young age at onset, lower peak temperature, short fever-to-seizure interval, and family history. Continuous or intermittent antiepileptic prophylaxis is not routinely recommended — the modest benefit does not outweigh adverse effects; antipyretics improve comfort but do not prevent recurrence. Provide clear return-precautions and seizure first-aid advice.
References
- AAP. Pediatrics. 2011;127(2):389–394 (neurodiagnostic evaluation of simple febrile seizure).
- AAP. Pediatrics. 2008;121(6):1281–1286 (long-term management).
- Nelson Textbook of Pediatrics, 21st ed.
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.