Examination of preserved stool specimens for parasites: lack of value of the direct wet mount

Abstract

To review the appropriateness of standard reference procedures for diagnostic parasitology, we examined 2,206 stool specimens in our laboratory by direct wet mounting with saline and iodine, by saline and iodine wet mounting from Formalin-ethyl acetate concentrates, and by permanent staining with Wheatley's modified trichrome method (W.B. Wheatley, Am. J. Clin. Pathol. 21: 990-991, 1951). Parasites were detected in 98 stool specimens (4.4%). In all but three specimens, direct wet mounting with saline and iodine contributed little significant information to the result yet consumed substantial technical time. We recommend that with preserved feces a direct examination not be performed but that examination of both a concentrate and a permanent stain be routine.

Detection of Dientamoeba fragilis in patients referred to Chaloos Medical Care Centers by nested – polymerase chain reaction (PCR) method

“…In a study in Turkey from 2007, 217 infected children with E. vermicularis, 99 cases (45.6%) were infected with D. fragilis (Girginkardesler et al, 2008). A study of wet mount and stained slides of 2206 patients from Durham city demonstrated that any D. fragilis was not seen in wet mount and in stained slides only one case was seen (Estevez and Levine, 1985). The role of Enterobius and other helminthes, if any, in the transmission of D. fragilis is still not clear.…”

“…Prevalence rate are reported between 0.4 to 91% that show the difficulties of diagnosis (Peek et al, 2004;Stark et al, 2005;. This parasite is not detectable by wet mount and since it does not have a cystic form it will be destroyed by concentration methods; so use of preservatives permanent staining are recommended for diagnosis (Johnson et al, 2004;Stark et al, 2005;Chan et al, 1993;Estevez and Levine, 1985). Prolonged staining methods used and accuracy of investigator caused focus on use of molecular methods.…”

Identification and Preservation of Intestinal Parasites Using Methylene Blue-Glycerol Mount: A New Approach to Stool Microscopy

“…The method is simple to perform, quick, and inexpensive, facilitating direct visualization of parasitic ova and cyst morphology. The disadvantage of this technique is that the preparation dries within a few minutes, rendering it unreadable and unreliable to visualize live nematodal larvae [ 7 ]. Each time a fresh preparation is required to view slides for later consultation or demonstration, which consumes considerable resources and technician's valuable time.…”

Justification for Use of a Single Trichrome Stain as the Sole Means for Routine Detection of Intestinal Parasites in Concentrated Stool Specimens

“…In the past, a thorough examination of stool specimens for detection of parasites involved four microscopic analyses: direct saline and iodine wet mounts of fresh (unpreserved) stool, an iodine wet mount of a concentrated sample, and a trichrome-stained smear of an unconcentrated sample (1,4,8). Because motile trophozoites cannot be detected in direct wet mounts of preserved specimens, many laboratories are now routinely performing only two microscopic analyses on stool specimens submitted for detection of parasites: trichrome staining of the unconcentrated sample and iodine staining of a wet mount of the concentrated specimen (2,4,14). In a continuing effort to maintain test sensitivity while reducing material and labor costs as well as exposure to toxic substances, including mercury and formaldehyde, there is an increasing interest in reevaluating the efficiency of older microscopic approaches and concepts, looking for more-rapid, less expensive, potentially less toxic, and equally sensitive alternatives.…”