Bottom line: Numerous reports from all over the world describe associations between diantamoeba fragilis and various GI symptoms, such as diarrhea.
Stark D, Barratt J, Roberts T, Marriott D, Harkness J, Ellis J. A review of the clinical presentation of dientamoebiasis. Am J Trop Med Hyg. 2010 Apr;82(4):614-619.
This review article states in its abstract, “Among 750 symptomatic and asymptomatic patients, Dientamoeba fragilis was detected at a prevalence of 5.2% and more common than Giardia intestinalis. Most infected patients presented with diarrhea and abdominal pain with symptoms greater than 2 weeks duration being common.”
Above article cites the following three articles.
Norberg A, Nord CE, Evengård B. Dientamoeba fragilis–a protozoal infection which may cause severe bowel distress. Clin Microbiol Infect. 2003 Jan;9(1):65-68.
This is a retrospective study of 87 patients diagnosed as being infected with the protozoan Dientamoeba fragilis. “A majority of the patients had symptoms of diarrhea, abdominal pain and flatus. The diarrhea varied from watery to loose, blood being reported only sporadically. Most patients had traveled outside Europe and had no other parasites in their stools. This study indicates potential pathologic properties in D. fragilis, and prospective studies are recommended.”
Johnson EH, Windsor JJ, Clark CG. Emerging from obscurity: biological, clinical, and diagnostic aspects of Dientamoeba fragilis. Clin Microbiol Rev. 2004 Jul;17(3):553-570. The opening lines of this review article’s abstract state, “Ever since its first description in 1918, Dientamoeba fragilis has struggled to gain recognition as a significant pathogen. There is little justification for this neglect, however, since there exists a growing body of case reports from numerous countries around the world that have linked this protozoal parasite to clinical manifestations such as diarrhea, abdominal pain, flatulence, and anorexia.”
Grendon JH, DiGiacomo RF, Frost FJ. Descriptive features of Dientamoeba fragilis infections. J Trop Med Hyg. 1995 Oct;98(5):309-315.
Abstract states, “A total of 237 cases of Dientamoeba fragilis were identified by a state public health laboratory in 1985 and 1986. Dientamoeba fragilis was the only parasite found in about two-thirds of the cases….Seventy-nine per cent of 70 interviewed D. fragilis cases reported symptoms associated with infection; nearly 80% had diarrhoea or loose stools.”