Introduction: Influenza virus outbreaks occur each year, in France, during autumn and winter. Influenza-associated acute encephalitis were reported during epidemics or pandemics. Sporadic cases are rarely identified probably because influenza virus is not searched among etiology of febrile encephalitis.
Exegesis: We report a case of influenza-associated encephalitis complicated by adrenal insufficiency in a young woman. Diagnosis was based on seroconversion of serum influenza virus A antibodies (complement fixation test). Follow up of the patient showed a total recovery.
Conclusion: Influenza must be searched for any febrile encephalitis occurring during winter. Reverse transcriptase polymerase chain reaction (RT-PCR) on cerebrospinal fluid should be assessed. It is not actually a routine technique and we do not know yet if it is accurate enough for diagnosis. So, it is important to identify influenza virus and obtain documentary evidence concerning neurological impairment. Nevertheless, a better understanding of pathogenesis and use of vaccination are needed to improve prognosis.