Infectious Disease Compendium

Blastocystis hominis


Protozoan. Various strains can be found in everything from fish to cockroaches.

Epidemiologic Risks

Common and found in up to 25% of US stools (PubMed).



Mostly diarrhea but perhaps not always pathogen, maybe perhaps don't treat it. If you feel that you must, try. Usually treat the symptomatic pateint with lots of cysts in stool and no other cause found (PubMed), since co-infection is common with Giardia, Entamoeba histolytica, and D. fragilis.


Self limited most of the time so maybe perhaps don't treat it. Metronidazole 750 or 500 tid x 10 days, iodoquinol, 650 tid for 10 to 20 days, TMP/Sulfa 2 DS qd for 7 days, nitazoxanide 500 bid for 3 days all inhibit in vitro. Review.


In most patients who have this in the stool and diarrhea, will, if you look hard enough, find another reason for the diarrhea.

Last update: 05/05/18