Four serologically different groups within the species Blastocystis hominis.

61 strains of Blastocystis hominis were isolated from 340 stool specimens coming from 140 patients with intestinal symptoms and from 200 healthy persons. The overall female to male ratio was 1.9 to 1. Classification of the 61 isolates of B. hominis was determined with the aid of the immunodiffusion assay. Four serologically different groups could be identified. Their frequency ratio in the population studied was 39.5%:39.5%:18%:3%. Group 3 was found more often than the other three groups in stool samples of patients. However, within the statistical deviation, none of the four immunological different groups was found to be correlated with the disease or the sex of the hosts.