 In the elderly, particularly those who have been treated with antibiotics for unrelated infections, a toxin produced by "Clostridioides difficile" often causes severe diarrhea.Parasites, particularly protozoa e.g., "Cryptosporidium" spp., "Giardia" spp., "Entamoeba histolytica", "Blastocystis" spp., "Cyclospora cayetanensis", are frequently the cause of diarrhea that involves chronic infection.The broad-spectrum antiparasitic agent nitazoxanide has shown efficacy against many diarrhea-causing parasites.