[Blastocystis hominis: a common commensal in the colon. Study of prevalence in different populations of Paris].

Objectives: To compare the prevalence of Blastocystis hominis in different population categories in Paris, including immunodepressed subjects.

Methods: Stool examinations were performed for 7,677 patients to determine the prevalence of Blastocystis hominis.

Results: Prevalence varied according to the population group: subjects free of any digestive tract disorders 17.4%; adults with digestive tract disorders 19.8% (this level was independent of digestive tract motility and of ethnic origin); children 13.8% (p < 0.01). In HIV-positive patients, the prevalence in immunocompetent patients was 19.6% compared with 15 to 16% in patients with AIDS (difference non significant). Blastocystis hominis was shown to be non-contagious in children and was not found to be sexually transmitted in homosexual men.

Conclusion: Generally, Blastocystis hominis infection resolves spontaneous before any manifestation of the protozoa. This common parasite is a commensal germ of the intestinal tract, even in subjects free of gastro-intestinal manifestations, and does not usually require prescription of an antibiotic. In exceptional cases with rapid proliferation, treatment can be proposed with nitroimidazol, particularly for certain strains with an abnormal variability.