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Blastocystis is a parasite with a worldwide distribution and a varying prevalence in different countries. The pleomorphic nature of the protozoon and the lack of understanding a possible pathogenesis have led to confusion regarding its clinical significance. The aim of the study was to shed light on clinical characteristics of pediatric patients in Swiss children with a positive stool sample for Blastocystis, in order to provide recommendations for a practical approach for the clinician to know whom, when, and how to test. This is a retrospective study of pediatric patients, whose stool has been tested positive for Blastocystis in the last 10 years in northern Switzerland. A total of 4047 stool samples, belonging to 1887 different patients, were analyzed; 240 stool samples (of 160 patients) were tested positive for Blastocystis. On average, 2.2 (CI 1.98-2.35) stool samples per patient were analyzed, of which 1.48 (CI 1.36-1.61) were positive for Blastocystis. In 63% abdominal pain was the leading symptom, while in 17.5% it was an accidental finding without symptoms. There was a high significance in correlation of abdominal pain and chronicity (p < 0.0001) but none in diarrhea (p = 0.082) nor nausea/vomiting or other symptoms and chronicity. Followed by Entamoeba coli (8%), 26.3% of the patients with Blastocystis had a co-infection with another parasite, mostly Endolimax nana (13%).Conclusion: Carriage of Blastocystis is common; therefore, only children/teenagers at risk for a symptomatic Blastocystis infection should be tested. There is a good correlation between Blastocystis and chronic abdominal pain. Children with abdominal symptoms persisting over 4 weeks should have two different stool samples analyzed. No screening after travels/immigration is recommended.What is Known:- Blastocystis has a worldwide distribution.- The clinical significance is unclear.What is New:- Based on retrospective data, we recommend to only test children/teenagers with chronic abdominal pain for Blastocystis.- Two different stool samples should be examined by microscopy; serological investigations are not warranted.
