Predisposing factors and characteristics of febrile seizures in children with influenza A infection were studied in children hospitalized with febrile seizures between January and July 2005 at Tuen Mun Hospital, Hong Kong. Of 177 children confirmed with influenza A infection, 34 (19.5%) had febrile seizures. Ages ranged from 0.9 to 6 years (mean 2.69 years); 19 males and 15 females. Age-matched controls had influenza A but no febrile seizures (control 1; n=34), and children with febrile seizures who tested negative for influenza (control 2; n=34). Mean maximum body temperature of children with febrile seizures and influenza A was 40.4 +/- 0.67°C, whereas in those without febrile seizures it was 38.7 +/- 1.8°C (P=0.04). Significant factors for development of febrile seizures in influenza included: family history of seizure disorders (P=0.03); history of febrile seizure (P=0.03); and coexisting gastroenteritis (P=0.05). History of febrile seizures was an independent risk factor (P=0.015). When compared to children with febrile seizures but negative influenza studies, those with confirmed influenza had a significantly higher maximum body temperature, shorter duration of fever before seizure onset, and more frequent occurrence of partial seizures. Current seizure was the first seizure in 26.5% influenza cases compared to 50% with negative viral studies (P=0.04). Febrile seizures were complex in 13 (38.2%) influenza positive vs 7 (20.6%) influenza negative cases. Duration of seizure was longer in the influenza group. 
COMMENT. Influenza A is a frequent cause of febrile seizures in China and Japan but not in the United States and Europe. A recent review of the role of viral infections in the etiology of febrile seizures [2, 3] concluded that fever and the height of the body temperature induced by infection is the essential factor. A threshold convulsive temperature dependent on the height of the body temperature has been established in animal and clinical studies, notably in patients with HHV-6 infection, the most common viral cause in the USA. A higher body temperature is also reported in the above series of influenza-induced febrile seizures. A specific neurotropism and CNS invasive property of HHV-6 is demonstrated in 14.5% of febrile seizure cases, using CSF-PCR analysis, and a similar neurotropic factor is suggested for influenza A virus. Only 2.5% HHV-6 cases tested showed CSF pleocytosis, a finding that tends to negate an encephalitic cause. Febrile seizures with influenza A are often complex, and difficult to differentiate from encephalopathy. Systemic immune and cytokine responses to influenza infection have also been invoked as factors. The association of influenza A and febrile seizures is seasonal, related to epidemics, especially prevalent in Asia, sometimes triggered by a concomitant reactivation of HHV infection, and often complicated by encephalopathy or complex seizures. The occurrence of febrile seizures with influenza A epidemics may also be viral strain dependent. Rapid viral diagnostic testing in patients presenting with complex febrile seizures during influenza season is recommended. Effective vaccination may prevent febrile seizures due to influenza.