A 22-year-old African-American woman comes to the emergency department because of low-grade fever, abdominal pain, and severe, watery, sometimes blood-tinged mucous diarrhea, with 10-15 stools per day for the last 48 hours. She says she has been drinking lots of liquids since the symptoms started, but remained diarrheic. One week ago, she had rhinorrhea with a purulent discharge, for which she received a prescription of amoxicillin. Her family history is unremarkable.
Vital signs on admission are BP 110/70 mmHg, HR 86 bpm, RR 16/min, and temperature 38.0°C (100.4°F). Her abdomen is soft, diffusely tender to palpation, with mild rebound tenderness. The remainder of the physical examination shows no abnormalities.
A complete blood count shows Hct 46%, Hb 13.1 mg/dL MCV 82 fl, MCHC 30 g/dL, WBC 16.200 /mm3. Na+ 138, K+ 4.8, Cl- 101. A plain abdominal radiograph is normal.
Antibiotic-associated colitis is suspected, and a rapid diagnosis is sought.
What is the most appropriate next step?
A) Sigmoidoscopy
B) Culture for Clostridium difficile
C) ELISA assay for Clostridium difficile toxin
D) Common antigen testing
E) Test for fecal leukocytes
