Incidence of Blastocystis hominis in faecal samples submitted for routine microbiological analysis.

Over a one-year period, 1390 faecal samples were submitted to Aberystwyth Public Health Laboratory for routine microbiological examination. All were stained using a commercial trichrome method. Blastocystis hominis was detected in 96 (6.9%), making it the most common parasite found in the study. Of the B. hominis-positive specimens, 73% were missed on direct microscopy. Molecular typing of B. hominis has revealed extensive genetic diversity in morphologically identical strains and thus detection by microscopy alone may not be sufficient to confirm the role of this organism in human disease.