The clinical significance of Dientamoeba fragilis and Blastocystis in human stool—retrospective cohort study

Objectives: The aim of this study was to assess the clinical significance of Dientamoeba fragilis (DF) and Blastocystis species (Bs) in human stool. Methods: Observational study of patients ≥18 years, who were tested by stool multiplex PCR for bacteria and parasites between April 2019 and March 2022. Although DF and Bs are part of the PCR kit, these results are not routinely reported to the patient or the ordering physician. The main outcomes were the incidence of symptoms during 14 days before the referral to stool PCR test, and the incidence of several clinical outcomes during 60 days after the PCR test (symptoms, referrals to further evaluation, prescription of symptomatic, or antibiotic treatment). Results: A total of 27 918 patients were tested by stool PCR during the 3 study years. A total of 6215 (22.3%) and 5337 (19.2%) were positive for DF and Bs, respectively. The incidence of symptoms before the test was similar in those positive for Bs or DF and those with all-negative PCR (adjusted OR and 95% CI of 0.87 [0.80–0.95] and 0.82 [0.76–0.88] for Bs and DF, respectively), whereas significantly higher (2.47 [2.23–2.73]) in those positive for the other multiplex PCR assay components. During the 60 days after the test, the prevalence of any of the outcomes was similar in those positive for Bs or DF and those with negative PCR (adjusted OR and 95% CI of 0.92 [0.83–1.02] and 0.89 [0.81–0.97] for symptoms, 0.84 [0.75–0.94] and 0.93 [0.85–1.01] for referrals, 0.88 [0.75–1.03] and 0.82 [0.71–0.94] for symptomatic treatment, and 0.88 [0.75–1.02] and 0.86 [0.75–0.98] for antibiotic treatment in the Bs and DF positive individuals, respectively). The PCR cycle threshold was not associated with any of the outcomes. Discussion: Positive stool PCR for DF or Bs was not associated with any of the measured clinical outcomes.