1. Prepared by Dr. Regina Kwon MD, MPH and reviewed by Dr. Sean Zhang MD, PhD

An adult patient presents to the emergency department with two weeks of diarrhea (7 to 10 episodes per day) and diffuse abdominal pain. They deny vomiting and fevers. Several months ago, soon after returning from international travel, they had been diagnosed with COVID-19 infection and provided steroids and supportive care. Due to persistence of symptoms as well as continued positivity for Sars-CoV2 nucleic acid, they were prescribed bamlanivimab infusion, which they received two months ago with subsequent relief.

A physical examination finds a tired-appearing, well-nourished adult patient in no acute distress. The abdomen is soft, nontender, and nondistended, with normal bowel sounds. There is no lymphadenopathy. Initial laboratory studies are shown below.

Stool microscopy is performed (Fig. 1).

Q. Which test is the best option to obtain a diagnosis?