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Journal of Clinical Microbiology, December 1999, p. 4113-4119, Vol. 37, No. 12
Division of Parasitic Diseases, Centers for
Disease Control and Prevention, Public Health Service, U.S.
Department of Health and Human Services, Atlanta, Georgia 30341
Received 23 June 1999/Returned for modification 24 July
1999/Accepted 20 August 1999
We undertook a study to evaluate Streck tissue fixative (STF) as a
substitute for formalin and polyvinyl alcohol (PVA) in fecal
preservation. A comparison of formalin, PVA, (mercuric chloride based),
and STF was done by aliquoting fecal samples into each fixative. Stool
specimens were collected in Haiti, and parasites included
Cyclospora cayetanensis, Giardia intestinalis,
Entamoeba coli, Iodamoeba butschlii,
Endolimax nana, Ascaris lumbricoides, Trichuris trichiura, Strongyloides stercoralis,
and Necator americanus. Preserved stools were examined at
various predetermined times (1 week, 1 month, and 3 months) to
establish the quality of the initial preservation as well as the
suitability of the fixative for long-term storage. At each time point,
stool samples in fixatives were examined microscopically as follows:
(i) in wet mounts (with bright-field and epifluorescence microscopy),
(ii) in modified acid-fast-, trichrome-, and safranin-stained smears,
and (iii) with two commercial test kits. At the time points examined,
morphologic features remained comparable for samples fixed with 10%
formalin and STF. For comparisons of STF- and 10% formalin-fixed
samples, specific findings showed that Cyclospora oocysts
retained full fluorescence, modified acid-fast- and safranin-stained
smears of Cryptosporidium and Cyclospora
oocysts were equal in staining quality, and results were comparable in
the immunofluorescence assay and enzyme immunoassay commercial kits.
Stool fixed in STF and stained with trichrome showed
less-than-acceptable staining quality compared with stool fixed in PVA.
STF provides an excellent substitute for formalin as a fixative in
routine examination of stool samples for parasites. However,
modifications to the trichrome staining procedures will be necessary to
improve the staining quality for protozoal cysts fixed in STF to a
level comparable to that with PVA.
0095-1137/99/$04.00+0
Evaluation of Streck Tissue Fixative, a
Nonformalin Fixative for Preservation of Stool Samples and
Subsequent Parasitologic Examination
*
Corresponding author. Mailing address: Div. Parasitic
Diseases/F-13, CDC, 4770 Buford Hwy., N.E., Atlanta, GA 30341-3724. Phone: (770) 488-4414. Fax: (770) 488-4253. E-mail:
ebk5{at}cdc.gov.
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