Intestinal protozoa such as Blastocystis species and Dientamoeba fragilis are frequently detected in Australian stool testing, particularly with the widespread use of polymerase chain reaction (PCR)-based diagnostics. Their clinical significance, however, remains nuanced. Australian clinical practice guidelines emphasize a cautious, symptom-guided approach to management rather than routine eradication.

Diagnostic Considerations:

In Australia, both Blastocystis and Dientamoeba fragilis are commonly identified in asymptomatic individuals. Detection alone does not equate to disease. Clinical guidelines stress that treatment decisions should be based on the presence of persistent, compatible gastrointestinal symptoms and the exclusion of alternative causes, such as celiac disease, inflammatory bowel disease, lactose intolerance, or functional gut disorders.

PCR testing is now the preferred diagnostic method due to its higher sensitivity, though it may increase detection of organisms with uncertain pathogenicity. For this reason, clinicians are advised to interpret results in the full clinical context rather than treating laboratory findings in isolation.

Blastocystis spp.: To Treat or Not to Treat:

Australian guidance generally regards Blastocystis as a commensal or low-pathogenicity organism in many individuals. Treatment is not recommended for asymptomatic patients. Treatment may be considered when the patient has persistent gastrointestinal symptoms (e.g., diarrhoea, abdominal pain, bloating), other causes have been reasonably excluded, and there is a temporal association between symptom onset and detection. First-line therapy in Australia typically includes metronidazole, although treatment response is variable and eradication does not always correlate with symptom resolution. This variability underpins the cautious stance in Australian guidelines.

Dientamoeba fragilis: Greater Clinical Relevance:

Unlike Blastocystis, Dientamoeba fragilis is more consistently associated with symptomatic infection in Australian practice. Symptoms may include chronic diarrhoea, abdominal pain, fatigue, and weight loss. Australian guidelines support treatment when Dientamoeba fragilis is detected in symptomatic patients. Recommended therapies include paromomycin (often preferred due to higher eradication rates) and metronidazole as an alternative option. Repeat testing may be considered in cases of persistent symptoms, although routine test-of-cure is not universally required if symptoms resolve.

Household Contacts and Reinfection

Australian recommendations do not routinely advise treatment of asymptomatic household contacts. However, in cases of recurrent infection or persistent symptoms, consideration may be given to testing close contacts, particularly in households with young children or shared bathroom facilities.

Emphasis is placed on hygiene measures, including handwashing and proper sanitation, to prevent reinfection and transmission.