Pathogenicity of Blastocystis hominis, a clinical reevaluation.

Blastocystis (B.) hominis was considered to be a member of normal intestinal flora in the past, but in recent years it has been accepted as a very controversial pathogenic protozoan. In this study, 52 individuals whose stool examination revealed B. hominis were evaluated for clinical symptoms. Metronidazole was administered for 2 weeks to the patients infected with B. hominis. After 2 weeks of treatment they were called for a follow-up stool examination. No other bacteriological and parasitological agents were found during stool examination of these patients. The frequency rate of intestinal symptoms was 88.4% in the B. hominis cases. Abdominal pain was the most frequent symptom (76.9%). Diarrhea and distention followed at a rate of 50.0% and 32.6%. Intestinal symptoms may be seen frequently together with the presence of B. hominis and this protozoan may be regarded as an intestinal pathogen, especially when other agents are eliminated.