Blastocystis hominis (stramenopila), an absolute anaerobic organism, has been considered a commensal of human large intestine, as even its massive invasion usually is asymptomatic. Nowadays, Blastocystis spp. has been mentioned more frequently as a potential etiologic agent of a chronic diarrhea, mainly among immunocompromised individuals, but also among patients with functional bowel disorders, malnourished, with chronic disease, or after organs transplantations. Blastocystis may also be responsible for traveler’s diarrhea.
Gastrointestinal disorders are quite common problems for individuals returning from different climatic and sanitary areas – countries located mainly in the tropics. Majority of such cases are patients suffering from self-limiting gastrointestinal tract. However, some patients, especially those who do not respond to empirical treatment in the primary health care, require more specialized diagnostics; this applies to the group of patients with prolonged diarrhea. Usually, they are caused by Escherichia coli infection. In this paper, we describe two travelers from Africa and India with prolonged diarrhea. The parasitic stool evaluation revealed massive Blastocystis hominis infestation. It was the reason to provide further diagnostics for acquired immunodeficiency, which gave the final diagnosis of HIV infection.