A 66-year-old man presents with fever, a severe headache, photophobia, nausea, and vomiting for 3 days. The headache was acute in onset, severe, unremitting, and generalized. It was worsened by sudden movements, but not by coughing or sneezing. His medical and surgical histories are unremarkable. He is not on any medications. A complete blood count is significant for a leukocyte count of 14,000/mm3 (normal: 4,600-11,000) with 90% neutrophils. C-reactive protein is 60 ng/mL (normal: <6)