Neuroinvasion of influenza A/H3N2: a fatal case in an immunocompetent adult.

Acute necrotizing encephalopathy (ANE) is a severe neurologic complication caused by influenza virus that has been infrequently reported in adult population. The diagnosis is made on epidemiological, clinical, and neuroimaging suspicion, but is rarely confirmed by microbiological findings in samples from the central nervous system (CNS), thus making it difficult to define the mechanism of pathogenesis of influenza-associated encephalitis/encephalopathies (IAE). We report a microbiologically documented case of ANE caused by influenza A/H3N2, in a previously healthy adult patient infected during a flu epidemic in Asturias (Spain). Direct viral invasion of the CNS was demonstrated with the isolation of the virus in a brain biopsy.