A 36-year-old man presented to the emergency department with a 2-week history of fever, headache, drowsiness, and photophobia. He was previously healthy and was sexually active with men. The physical examination was notable for a temperature of 38.3°C and neck stiffness. Computed tomography of the head was normal. The opening pressure on lumbar puncture was 29 cm of water (reference range, <20 cm). The cerebrospinal fluid (CSF) cell count was 340 cells per microliter (reference range, 0 to 10), with 90% mononuclear cells, which were predominantly lymphocytes.

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