A 56-year-old man returns from a camping trip during which he drank water from a river. He now reports nausea, abdominal pain, and grossly nonbloody stools that float. A stool test for pathogens is indeterminate. The most appropriate next diagnostic test is:

There's more to see -- the rest of this topic is available only to subscribers.

All content is protected by copyright and may not be used for AI model training or other unauthorized purposes.