It's just good practice to run a white blood cell count any time someone comes in with a high fever, or in older people especially, sudden-onset confusion.
My mom had a terrible urinary tract infection, and the *only* symptom she showed was extreme confusion. She wasn't hurting anywhere and wasn't spiking a fever. Even her urine wasn't testing as infected. The only sign she had was an elevated white blood cell count. Finally, her urine culture did grow out bacteria, but it wasn't until she was nearly delirious.
Fortunately, her ER doctor had the sense to order a full blood panel, which clearly showed a very high white count, bordering on septicemia. She was admitted to the hospital and started on IV antibiotics that day.