A 64-year-old woman is hospitalized for pneumonia and has be…
A 64-year-old woman is hospitalized for pneumonia and has been receiving broad-spectrum antibiotics (cefepime and vancomycin) for 10 days. She now reports profuse watery diarrhea (8 stools/day), abdominal cramping, and low-grade fever. Vitals: T 100.9°F, BP 106/68, HR 102. Labs: WBC 15,000/µL, creatinine 1.8 mg/dL (baseline 0.9). Stool is heme-negative. Which diagnosis is of greatest concern?