A patient presents with watery diarrhea after travel to Mexico. Initial stool ova-and-parasite microscopy is negative, but giardiasis remains strongly suspected. Which test most sensitively confirms Giardia lamblia infection?
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Correct answer: PCR stool panel
A stool PCR (multiplex GI pathogen panel) is the most sensitive method for confirming Giardia and can detect infection even when microscopy is negative, because cyst and trophozoite shedding is intermittent. Serologic IgG cannot distinguish current from past infection, and Giardia is a luminal intestinal parasite that is not recovered by blood culture or identified by Western blot.
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