An evaluation of quantitative techniques for Schistosoma haematobium eggs in urine preserved with carbolfuchsin

The objective of this study was to determine a suitable method for quantitating Schistosoma haematobium eggs in urine specimens preserved in carbolfuchsin. Using a 0.002% carbolfuchsin-phenol-alcohol solution as a stain/preservative for urine obtained from 30 patients infected with S. haematobium, we compared egg counts obtained with four quantitative techniques: Nytrel filtration, Nuclepore filtration, suction filtration and centrifugation. Centrifugation gave statistically higher values than all other techniques for absolute number of eggs recovered in the preserved urine. We also measure a statistical difference between the counts obtained from Nuclepore filtration of fresh urine and those established on an equivalent volume of preserved urine by Nuclepore and Nytrel filtration. The preserved urine frequently caused obstruction of both Nuclepore filters and Whatman No. 1 filters (used in suction filtration), rendering them technically difficult to use and less satisfactory than other methods. From the techniques we examined, we conclude that in field studies where preservation of urine is necessary, preparation of Nuclepore filters with fresh urine, or centrifugation of a carbolfuchsin-preserved urine, are the methods of choice for quantitation of specimens.