Many laboratories in the UK would not be able to exclude D. fragilis and B. hominis, therefore it is possible that some patients infected with these parasites could be misdiagnosed as having IBS. Anecdotal evidence suggests that many patients infected with these parasites are indeed being misdiagnosed as having IBS.

D. fraglis and B. hominis: neglected human protozoa. J. J. Windsor. The Biomedical Scientist. July 2007. Pages 524-27.

The clinical consequences of B. hominis infection are mainly diarrhea or abdominal pain with nonspecific gastrointestinal symptoms such as nausea, anorexia, vomiting, weight loss, lassitude, dizziness, and flatulence.

Irritable Bowel Syndrome: In search of an etiology: role of B. hominis. Javed Yakoob et al. Am. J. Trop. Med. Hyg., 70(4), 2004, pp. 383-385

Most recent literature accepts that D. fragilis is an important enteric pathogen with an estimated incidence of symptomatic infection of between 4 and 91%. Symptoms include abdominal pain, bloating, and diarrhea.

Peek et al, 2004, American Society for Microbiology

"The clinical consequences of B. hominis infection are mainly diarrhea and abdominal pain as well as nonspecific gastrointestinal symptoms such as nausea, anorexia, vomiting, weight loss, lassitude, dizziness, and flatulence. Case reports and series have suggested a pathogenic role of B. hominis in causing intestinal inflammation. Also some studies have suggested that inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) are associated with B. hominis infection. The investigators indicate that the stools of all patients presenting with IBD or IBS should be examined, and culture methods for B. hominis carried out. Invasion and mucosal inflammation of the intestine with B. hominis have been observed in studies of gnotobiotic guinea pigs."

Blastocystis hominis and bowel diseases. Turkiye Parazitol Derg. 2006;30(1):72-76

The search for Blastocystis hominis should be a parasitological routine analysis since it is the cause of frequent intestinal disorders.

Ponce de Leon P, Svetaz MJ, Zdero M. Rev Latinoam Microbiol. 1991 Apr-Sep;33(2-3):159-64