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Retortamonas intestinalis, a nonpathogenic flagellate.
Both cysts and trophozoites of Retortamonas intestinalis are shed in feces. Infection occurs after the ingestion of cysts in fecal-contaminated food or water, or on fomites. In the large (and possibly small) intestine, excystation releases trophozoites. Retortamonas resides in the large intestine, where it is regarded as a commensal and is not known to cause disease.
Retortamonas intestinalis is considered nonpathogenic. The presence of trophozoites and/or cysts in stool specimens can however be an indicator of fecal contamination of a food or water source, and thus does not rule-out other parasitic infections.