The Water Was Warm

A previously healthy 28-year-old man presents to a Texas emergency department in late July with two days of severe frontal headache, fever to 40.2 C, nausea, and three episodes of vomiting. This morning he developed worsening confusion and his wife noticed he was no longer able to identify familiar smells. He swam in a warm, stagnant lake four days ago while on a weekend camping trip.

On examination his temperature is 39.8 C, heart rate 118/min, blood pressure 142/88 mmHg, and respiratory rate 20/min. He is lethargic and oriented only to person. Nuchal rigidity and a positive Kernig's sign are present. Cranial nerve examination is otherwise intact, and there are no focal motor deficits. He reports complete loss of smell since yesterday.

Laboratory studies show white blood cells 22.4 x 10^3/uL with 88% neutrophils, sodium 128 mEq/L, glucose 142 mg/dL, creatinine 1.1 mg/dL, and C-reactive protein 84 mg/L. CT head without contrast shows no acute intracranial abnormality. Lumbar puncture reveals an opening pressure of 320 mm H2O. Cerebrospinal fluid analysis shows white blood cells 4,200/uL with 91% neutrophils, 450 red blood cells, glucose 24 mg/dL (serum glucose 142), and protein 410 mg/dL. Gram stain shows no organisms.

Empiric ceftriaxone, vancomycin, and acyclovir are started for presumed bacterial meningitis with HSV encephalitis coverage. Thirty minutes later, the microbiology laboratory calls the clinical team: the technician prepared a wet mount from the patient's fresh, room-temperature CSF and observed several large, slowly motile cells with blunt lobate pseudopods and a prominent central karyosome.