The Kato-Katz technique has been widely employed in the investigation of helminthic eggs in faeces. Sometimes, however, stool specimens must be preserved, specially in field surveys, in order to allow transport and improve feasibility. In an attempt to use a solid preservative, capable of keeping the morphology of Schistosoma mansoni eggs intact, blocking parasite development, without interfering with the usual glycerin clarification method, the authors have added 2-3 mg sodium azide (NaN3) to stools. Each specimen contained about 2 g stools and was obtained from patients, who eliminated a known egg burden, determined by the Kato-Katz' technique. Stools with sodium azide were kept at room temperature and submitted to subsequent egg counts after one, two, four, eight and twelve weeks. Examinations were carried out in 53 stool specimens and showed that egg structure was preserved and egg counts remained almost identical in 51 of them. Two specimens, examined after eight and twelve weeks, where dehydrated and unsuitable for egg counts. Therefore the authors regard sodium azide as an adequate chemical preservative for stool specimens to be submitted to egg counts by the Kato-Katz' technique.
Schistosomiasis mansoni; Laboratory diagnosis; Stool preservation; Kato-Katz' technique