A tale of two studies: is peripheral eosinophilia associated with Dientamoeba fragilis detection in adult stool samples?

The protozoan parasite Dientamoeba fragilis is a frequently isolated stool organism and postulated cause of gastrointestinal symptoms. Peripheral blood eosinophilia has been described. This is the first study amongst the Australasian adult population to assess the relationship between organism detection and eosinophilia.

A case-control study took place over 7 years at a single Sydney laboratory site, evaluating patients with D. fragilis identified on stool using real-time PCR with a recent full blood count, to control groups with Giardia spp. and sequential negatives with neither organism. A nested study compared those with microscopic evidence of D. fragilis as a marker of disease burden, to molecular diagnosis alone.

Sixty-four D. fragilis, 30 Giardia spp., and 94 sequential controls were enrolled. Only 60.1% of samples were preserved in sodium acetate-acetic acid formalin (SAF) fixative, indication mostly not documented. The major co-organism detected amongst all participants was Blastocystis sp., particularly in the D. fragilis cohort (37.2%). The most common pathogen amongst sequential controls was Campylobacter spp. (7.4%). Patients with D. fragilis were more likely (12.5%) to have a clinically significant eosinophilia (>0.5×10⁹/L) compared to those with Giardia spp. (3.3%) or sequential controls (4.3%) (p=0.03). A significant difference was also noted in the overall median eosinophil count of those with D. fragilis versus all controls (0.2 vs 0.1×10⁹/L, p=0.01); however, this was within the reference interval (where up to >0.5×10⁹/L is accepted in healthy individuals within a typical population). No eosinophil difference was found between those with molecular versus additional microscopic detection of D. fragilis (0.1 vs 0.1×10⁹/L).

These results support an association between the identification of clinically significant peripheral blood eosinophilia and D. fragilis presence, which may impact the diagnostic approach to the patient with unexplained eosinophilia. Further prospective trials may help assess any significance further and the implication of co-carriage with other enteric organisms. The importance of clinical indication and need for appropriate fixative media in diagnostic parasitology are also highlighted.