Molecular Detection of Dientamoeba fragilis and Its Association with Gastrointestinal Symptoms in Iraqi Patients

Background: Dientamoeba fragilis is a trichomonad protozoan of the human large intestine whose pathogenic role remains debated. Conventional microscopy underestimates its frequency, and no molecular data from symptomatic and asymptomatic Iraqi populations attending private clinics have been reported. This study aimed to determine the prevalence of D. fragilis by real-time polymerase chain reaction (PCR) in patients attending private clinics in Baghdad and to evaluate its association with gastrointestinal symptoms and potential risk factors. Methods: A case-control study was conducted from 2022 to 2026 in 3 private clinics in Baghdad, Iraq. Single fresh stool samples were collected from 250 patients with gastrointestinal symptoms (cases) and 100 asymptomatic individuals (controls). Samples were examined by direct wet mount and permanent iron-haematoxylin staining, and DNA was extracted for real-time PCR targeting the 5.8S ribosomal RNA gene region of D. fragilis. Demographic, environmental and clinical data were collected using a structured questionnaire. Associations were assessed by chi-square tests and multivariable logistic regression. Results: D. fragilis DNA was detected in 57 of 350 participants (16.3%), compared with 21 (6.0%) by microscopy. Microscopy showed a sensitivity of 36.8% relative to PCR, with moderate agreement (κ = 0.49). Positivity was higher in symptomatic patients than in controls (19.2% vs 9.0%; OR 2.40, 95% CI 1.13–5.10; p = 0.020). Among symptomatic patients, infection was associated with abdominal pain (p = 0.029), bloating (p = 0.025), anal pruritus (p = 0.035) and symptom duration longer than two weeks (p = 0.034), but not with diarrhoea, nausea or vomiting. In multivariable analysis, age under 20 years (aOR 1.92), use of untreated water (aOR 2.71) and presence of gastrointestinal symptoms (aOR 2.29) were independently associated with infection. In conclusion, D. fragilis is frequently present in clients in private clinics in Baghdad and is largely underreported by routine microscopy. The association of this parasite with abdominal pain, bloating, and chronic symptoms should lead to the inclusion of a molecular test in the diagnostic procedures of unexplained gastrointestinal symptoms in Iraq.