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. LEARNING POINTS: 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. © EFIM 2021.