Faecal preservation with azide for diagnosis of helminthic infection by direct examination - abstract

ABSTRACT

Direct examination of a cleared sample of faeces is a simpl, reliable and quantitative method for the diagnosis of helminthic ingection. As such, it is preferred to the cumbersome and less precise formalin preservation and concentration techniques. These latter method have had to be used in experiments or surveys where ther is a delay in analysis because established direct techniques required fresh, undiluted faeces. This study tested sodium azide as a preservative of faeces for later direct quantitative egg counts. Gresh faeces from chilren known to have Trichocephalus trichuris infection were each pressed through a 100-mesh sieve to remove fibre. Quadruplicate 50 mg aliquots of fresh stool were prepared and examined by the Kato thick-smear technique (Martin and Beaver, Amer J. Trop. Med. & Hyg., 17382-391, 1968) and the eggs counted. 1.5 to 2g of faeces was stirred thoroughly using a match-stick with 6 mg of powdered sodium azide in a 4 ml autoanalyser cup. The container was capped and stored at ambient temperature (circa 25§C). Egg counts were repeated at intervals. There was no evidence of fermentation of the stool. The mean egg counts of fresh stool and after preservation for 1, 2 and 4 week were 126 ñ 45, 128 ñ 44, 124 ñ 46 and 137 ñ 49. The standard deviation of the differences between the fresh samples and the preserved samples were 11, 10 and 16 respectively. None of these differences were significant. Stools from children containing T. trichuris, Necator americanus, and fertile and infertile Ascaris eggs were photographed whilst fresh and after azide preservation for up to 6 months. The morphology of the eggs appeared unchaged during this time. The azide preservation technique has made available direct quantitative analysis of stools in situations where stool must be preserved. It has been successfully used in a survey of the Turks and Caicos Islands where samples were transported to Jamaica for analysis (AU)