Performance of para-Pak Ultra ECOFIX compared with Para-Pak Ultra formalin/mercuric chloride-based polyvinyl alcohol for concentration and permanent stained smears of stool parasites.

Abstract ECOFIX™ is a mercury and formalin-free fecal preservative that can be used for concentration of stool specimens and preparation of permanently-stained slides. In this study, the standard two-vial ParaPak™ Ultra system was compared with ECOFIX™ Ultra for the detection of intestinal parasites. A total of 261 specimens in 92 sets (77 with 3 specimens, 15 with 2 specimens) were collected in ECOFIX™, formalin, and low viscosity polyvinyl alcohol (LV-PVA). Concentrations were performed from ECOFIX™ using Hemo-De and saline and from formalin using ethyl acetate and formalin. To prepare permanently-stained smears, ECOSTAIN™ (a modification of Wheatley's trichrome stain) was used on ECOFIX™ material and Wheatley's trichrome stain was used on specimens preserved in PVA. A total of 157 protozoa and helminths were detected; 132 (84.1%) were recovered in formalin/PVA and 129 (82.2%) in ECOFIX™. In permanently-stained smears, 139 protozoa were observed, 116 (83.5%) in PVA-preserved material and 117 (84.2%) in ECOFIX™. Fecal concentration yielded 111 parasites (103 protozoa and 8 helminths), of which 98 (88.3%) were detected in formalin-fixed stool and 48 (43.2%) in ECOFIX™. Significantly fewer ECOFIX™-preserved concentrates were positive for Blastocystis hominis (35 versus 15, p -value Endolimax nana (19 versus 2, p -value