Comparison of polyvinyl alcohol fixative with three less hazardous fixatives for detection and identification of intestinal parasites

Polyvinyl alcohol (PVA) containing the fixative mercuric chloride is consid ered the "gold standard" for the fixation of ova and parasites in the prepa ration of permanently stained smears of stool specimens. However, mercuric chloride is potentially hazardous to laboratory personnel and presents disp osal problems, We compared three new alternative, nontoxic fixatives with P VA, analyzing ease of sample preparation and quality of smears. Sixty-eight fresh stool specimens were divided into aliquots and placed in each of fou r different fixatives: PARASAFE (PS) (Scientific Devices Laboratory, Inc., Des Plaines, Ill.), ECOFIX (EC) (Meridian Diagnostics, Inc,, Cincinnati, Oh io), Proto-Fix (PF) (Alpha-Tec Systems, Inc., Vancouver, Wash.), and ion: v iscosity PVA fixative (PVA) (Meridian), Specimens were processed and staine d according to each manufacturer's directions. Parasites were found in 31 o f 68 slide preparations with PVA, 31 with PF, 30 with EC, and 30 with PS, B lastocystis hominis and Iodamoeba butschlii were preserved in a readily ide ntifiable state by all methods of fixation, However, some parasites were mo re easily identified with some of the fixatives because of differences in p arasite distortion. For example, Entamoeba histolytica (Entamoeba dispar) w as detected in 13 stools fixed with PF, 7 with PVA, and 6 with EC but none with PS, Likewise, Chilomastix mesnili was identified in 13 specimens fixed with PF, 8 with EC, and 5 with PVA but only 1 with PS, while Entamoeba col i was seen much less frequently with PS than with the other three fixatives , A dirty background was observed in 41% of specimens prepared with PS, whe reas background quality was acceptable with other fixatives.. Sample prepar ation was most rapid with PS, although the EC method involved the fewest st eps. In conclusion, PVA and PF produced the least parasite distortion, whil e PS proved unsatisfactory fur the identification of E. histolytica, E. col i, and C. mesnili. Both PF and EC appear to be acceptable, environmentally safe substitutes for PVA.