A 62-year-old woman is transferred from an outpatient clinic to an acute care unit due to a gradually worsening illness over the past five days. Initially, she experienced a persistent cough, low-grade fever, and muscle aches. Over the last 48 hours, her symptoms have progressed significantly to include severe headache, profound confusion, watery diarrhea, and diffuse abdominal discomfort. She denies any recent foreign travel but mentions a stay at a hotel with a large indoor pool two weeks prior to symptom onset. On examination, her temperature is 39.40C, blood pressure is 118/72 mmHg, pulse is 115/min, respirations are 20/min, and oxygen saturation is 92% on room air. Physical examination reveals bilateral inspiratory crackles, more pronounced in the left lower lobe, and dullness to percussion. She is disoriented to time and place, and her Glasgow Coma Scale score is 13 (E4V4M5). Initial laboratory studies are performed. Considering these findings, what are the most appropriate initial diagnostic steps and empiric management strategy for this patient?