A 78-Year-Old Woman Who Resides in an Assisted Living Facility

A 78-year-old woman who resides in an assisted living facility is brought to the emergency department after having a tonic-clonic seizure.  Her caretakers state that the patient became mildly confused and had a headache yesterday.  Earlier today, the patient had involuntary shaking of her right upper and lower extremities followed by a generalized tonic-clonic seizure.  The patient's family reports that she has not had any sick contacts or recent travel.  She has no cough, shortness of breath, diarrhea, or urinary symptoms.  Her other medical problems include hypertension and hyperlipidemia.  The patient has no known allergies.
Her temperature is 38.1 C (100.8 F) , blood pressure is 140/88 mm Hg, pulse is 90/min and regular, respirations are 13/min, and oxygen saturation is 98% on room air.  The general physical examination is unremarkable.  On neurologic examination, the patient appears obtunded and does not follow commands.  On manual motor testing, she is able to localize to pain bilaterally and to withdraw her lower extremities to pain.
A non-contrast head CT shows no mass, bleeding, or parenchymal abnormalities.  Chest x-ray shows no infiltrates.  Urinalysis shows clear urine, negative nitrites, negative leukocyte esterase, 5−10 leukocytes/hpf, and few bacteria.  A lumbar puncture is attempted but is unsuccessful.  Intravenous vancomycin, ampicillin, and ceftriaxone are administered.
Which of the following is the best next step in management of this patient?

A) Add intravenous acyclovir
B) Add rifampin
C) Perform bedside electroencephalogram monitoring
D) Perform MRI of the brain with and without gadolinium
E) Switch from ceftriaxone to cefepime