A Seasonal Cause of Encephalitis: Influenza Virus A (H3N1) Infection

Influenza virus infection can have a range of presentations, from asymptomatic to life-threatening disease. We present the case of a 57-year-old woman with a known history of schizophrenia (controlled with medication) who presented to our emergency department in a coma after experiencing a seizure. She had reported flu-like symptoms in the previous week, which evolved to dyspnoea and altered mental status culminating in seizures and coma. Influenza virus A (H3N1) was identified in the cerebrospinal fluid. Although a rare cause of encephalitis, the influenza virus should be considered in the differential diagnosis, especially during epidemics.

Influenza virus encephalitis should be considered in some specific settings, such as during pandemics or seasonal epidemics.Altered mental status in a patient with a history of mental disease may be easily dismissed as secondary to prior disease or medication.Although rare, extrapulmonary manifestations of influenza virus infection can be serious and fatal.