Health care-associated diarrhea — ABIM Board MCQ

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EasyGeneral Internal MedicineHealth care-associated diarrheaABIM Board

A 75-year-old hospitalized man develops 5 watery stools over the past 24 hours after receiving broad-spectrum antibiotics for 6 days. He has abdominal cramping and leukocytosis. He has received no laxatives or stool softeners. Which of the following is the most appropriate diagnostic study?

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Correct answer: D — Stool testing for toxigenic Clostridioides difficile

The correct answer is D. This patient has new-onset, unexplained diarrhea with at least 3 unformed stools in 24 hours plus major risk factors for Clostridioides difficile infection: advanced age, hospitalization, and recent broad-spectrum antibiotic exposure. An unformed stool specimen should be tested using the institution's validated C difficile assay—either NAAT alone when strict specimen-submission criteria are enforced or a multistep algorithm incorporating toxin testing. Ova and parasite examination and routine bacterial culture are not first-line studies for typical hospital-onset antibiotic-associated diarrhea without relevant exposures. Fecal calprotectin is a nonspecific marker of intestinal inflammation. Colonoscopy is unnecessary initially and is generally reserved for unusual cases in which stool testing is unavailable or nondiagnostic despite strong suspicion.

Reference: Infectious Diseases Society of America and American Society for Microbiology. Guide to Utilization of the Microbiology Laboratory for Diagnosis of Infectious Diseases: 2024 Update, Clostridioides difficile section. 2024. https://www.idsociety.org/globalassets/idsa/practice-guidelines/ciae104.pdf