2022 Volume 71 Issue 1 Pages 148-152
Blastocystis hominis is a protozoan that parasitizes the human large intestine and causes diarrhea and vomiting, but its pathogenicity remains unclear. In this paper, we report a case of diarrhea that was suspected to be due to B. hominis infection and was diagnosed on the basis of the results of staining methods. A man in his 80s had persistent diarrhea that was suspected to be due to a parasitic infection on the basis of Gram staining of his stool. Direct thin-layer smearing of the stool confirmed the parasite to be B. hominis. The reasons for considering this case as diarrhea caused by B. hominis were as follows: (1) trophozoites were detected, (2) no causative agent of diarrhea was identified, (3) the blood eosinophil count was high, and (4) digestive symptoms and eosinophilia were improved by taking metronidazole. However, since the causal relationship between (3) and (4) is not clear, it cannot be said that the diarrhea was caused by B. hominis, but it could be a case in which eosinophilia due to parasites was presumed. We attempted to compare techniques of staining B. hominis. The differential staining methods used were Gram staining, iodine staining, and Giemsa staining. Sternheimer (S) staining used for urine sediments was also performed. The stainability was good for all these methods. Our results suggest that S staining was the best method for observing internal structures. Since this simple and easy S staining can be performed in a relatively large number of facilities, it was considered an effective staining method for detecting B. hominis.
