A 50-year-old woman with type I diabetes mellitus is admitted to hospital for a 2-day history of fatigue, fever, and confusion. Current medications include metformin, lisinopril, and simvastatin. Temperature is 101 F, HR 90, BP 150/90. A CT of the head shows no abnormalities. EEG shows spike-complexes over the temporal region. Lumbar puncture is performed. CSF findings are shown:
Protein 50 mg/dL (NR 15-60)
Glucose 70 mg/dL (NR 50-100)
Cells 40/μL; lymphocytes (NR 0-8)
RBC 50/μL (NR <1)
Which of the following is the most likely explanation for these findings?