Approach to nosocomial infections Quiz: Ace Your Exams

A 72-year-old woman is evaluated on the fourth day of hospitalization. The patient presented with acute gangrenous cholecystitis with resultant septic shock that was treated with intravenous norepinephrine (via a central venous catheter) and piperacillin-tazobactam followed by open cholecystectomy. The patient has not had a bowel movement since the surgery. The patient was recovering well until this morning when she developed moderate abdominal pain and lethargy. On physical exam, the patient has hypoactive bowel sounds and diffuse abdominal tenderness without rebound or guarding. Pulmonary examination is normal. Temperature is 38.5 ºC (101.3 ºF), pulse is 96/min, blood pressure is 110/72 mmHg, and oxygen saturation is 99% on room air. Serum white blood cell count is 22,000/mm³. Three to five white blood cells/hpf are present in the urine and the stool. Urinalysis is negative for leukocyte esterase and nitrites. Procalcitonin is 0.03 ng/mL (≤0.15 ng/mL). Blood cultures are sent and come back negative. Urine culture is pending. Which of the following tests is most likely to be positive and confirm the underlying cause of her signs and symptoms?