Study of Blastocystis hominis isolates in urticaria: a case-control study.

Blastocystis hominis is a common intestinal parasite, with a prevalence in developing countries of up to 50%. The aim of this study was to investigate the association of this parasite with urticaria by determining the genotypic isotypes in the Egyptian population. In total, 54 patients with urticaria and 50 controls were enrolled in the study. Stool samples were examined and assessed by PCR. The parasite was detected in a significantly higher number (P < 0.001) of the patient group than the control group. There was no significant difference between the patients with acute and those with chronic urticaria (P = 0.2). The amoeboid form was found in 60.6% of Blastocystis-positive patients with urticaria, but in none of the healthy controls. Subtype 3 was the only isolate found in both the patient and control groups. We recommend treatment for Blastocystis-positive patients with urticaria in developing countries. The prevalence is much lower (around 10%) in developed countries, where treatment should only be considered in the absence of other possible causes of urticaria.