Dientamoeba fragilis is a single-celled parasite which infects the large intestine causing diarrhea, gas, and abdominal pain. An Australian study identified patients with symptoms of IBS who were actually infected with Dientamoeba fragilis. Their symptoms resolved following treatment. A study in Denmark identified a high incidence Dientamoeba fragilis infection in a group of patients suspected of having gastrointestinal illness of an infectious cause. The study also suggested special methods may be required to identify infection.