ARTICLE Low prevalence of Blastocystis sp. in active ulcerative colitis

Abstract Ulcerative colitis (UC) is thought to originate from a disbalance in the interplay between the gut microbiota and the innate and adaptive immune system. Apart from the bac-terial microbiota, there might be other organisms, such as parasites or viruses, that could play a role in the aetiology of UC. The primary objective of this study was to compare the prevalence of Blastocystis sp. in a cohort of patients with active UC and compare that to the prevalence in healthy con-trols. We studied patients with active UC confirmed by endos-copy included in a randomised prospective trial on the faecal transplantation for UC. A cohort of healthy subjects who served as donors in randomised trials on faecal transplantation were controls. Healthy subjects did not have gastrointestinal symptoms and were extensively screened for infectious dis-eases by a screenings questionnaire, extensive serologic as-sessment for viruses and stool analysis. Potential parasitic in-fections such as Blastocystis were diagnosed with the triple faeces test (TFT). The prevalence of Blastocystis sp. were compared between groups by Chi-square testing. A total of 168 subjects were included, of whom 45 had active UC [me-dian age 39.0 years, interquartile range (IQR) 32.5–49.0, 49% male] and 123 were healthy subjects (median age 27 years, IQR 22.0–37.0, 54 % male). Blastocystis sp. was present in the faeces of 40/123 (32.5 %) healthy subjects and 6/45 (13.3 %) UC patients (p=0.014). Infection with Blastocystis is significantly less frequent in UC patients as compared to healthy controls