Which parasite is commonly associated with traveler’s diarrhea and is detectable by stool antigen testing?

• A. Giardia lamblia
• B. Entamoeba histolytica
• C. Strongyloides stercoralis
• D. Ascaris lumbricoides

Answer: (C)

Stool antigen testing is designed to detect Giardia lamblia in stool, and Giardia is a classic cause of traveler’s diarrhea from ingesting cysts in contaminated water or food. The coproantigen immunoassay is a common, sensitive way to confirm giardiasis quickly, often more reliable than looking for organisms under the microscope. While other parasites like Entamoeba histolytica can cause diarrhea and have antigen tests, Giardia remains the most typical traveler’s-diarrhea parasite that is routinely detected by stool antigen testing. Strongyloides stercoralis and Ascaris lumbricoides are usually diagnosed by stool larvae or eggs or serology rather than a standard stool antigen test, and their presentation is less characteristically traveler’s diarrhea.