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P667. Low prevalence of Blastocystis sp. in active ulcerative colitis patients

N. Rossen1, A. Bart2, N. Verhaar2, E. van Nood3, R. Kootte4, P. de Groot3, M. Nieuwdorp4, G. D'Haens1, C. Ponsioen1, T. van Gool2, 1Academic Medical Center, Gastroenterology & Hepatology, Amsterdam, Netherlands, 2Academic Medical Center Amsterdam, Department of Medical Microbiology, Parasitology Section, Amsterdam, Netherlands, 3Academic Medical Center Amsterdam, Department of Internal Medicine, Amsterdam, Netherlands, 4Academic Medical Center Amsterdam, Department of Vascular Medicine, Amsterdam, Netherlands


Ulcerative colitis (UC) is supposed to originate from a disbalance in the interplay between the gut microbiota and the innate and adaptive immune system. Apart from the microbiota, there might be other members; such as parasites, that could play a role in UC. The prevalence of Blastocystis in industrialised countries is decreasing whereas in the developing world chronic infestation is much more common, while the prevalence of ulcerative colitis shows the opposite. The primary objective of this study is to compare Blastocystis prevalence in a well-defined cohort of active ulcerative colitis patients compared to extensively ascertained healthy controls.


Clinically and endoscopically active UC patients, participating in a clinical trial and extensively tested healthy subjects, participating in the same trial as faecal donors were included. Healthy subjects did not have gastrointestinal symptoms, did not travel to an underdeveloped country within 6 months before inclusion and were extensively screened for infectious diseases by a screenings questionnaire, as well as serology and stool cultures. Diagnosis of intestinal parasites was performed with the Triple Faeces Test (TFT), a reliable method for detection of intestinal parasites; especially also Blastocystis sp. Healthy subjects did not use medication. UC patients were not allowed to use anti-TNF medication or Prednisolone >10 mg daily. Both groups did not use antibiotic treatment within 6 weeks before inclusion.


169 subjects were included; 45 UC patients (median age 39.0 years (IQR 33–49), 49% male) and 124 healthy subjects (median age 27 years (IQR 22–38), 54% male). Healthy subjects were significantly younger than UC patients (P < 0.001). Median disease duration of UC was 9 years (range 0–27), 64.4% of UC patients used oral mesalazine, 29% used rectal mesalazine or corticosteroids, 29% used thiopurines and 20% used systemic corticosteroids. The prevalence of Blastocystis sp was 40/124 (32%) in healthy subjects and 6/45 (13%) in UC patients (P < 0.05). There was no association between the use of mesalazine, immunosuppressants or corticosteroids and the presence of parasites in UC patients.


Infection with Blastocystis is significantly less frequent in ulcerative colitis patients as compared to healthy controls.