Question

A 3-week old baby girl is sent to your emergency department after being seen by their pediatrician for irritability, poor feeding, and a seizure just prior to arrival at the pediatrician’s office. Vital signs are BP-103/73, HR-137, RR-25, O2-100% on room air, and Temp-39.2oC (102.5oF). Physical examination reveals a lethargic infant with decreased motor tone and a full, bulging frontal fontanelle. What is the most important diagnostic study to obtain and what is the empiric treatment of choice while awaiting results?