Field evaluation of an improved Kato-Katz thick smear technique for quantitative determination of helminth eggs in faeces.

A new method for the quantification of helminth eggs in faeces was developed, in which 7.5% nigrosin in 10% formaldehyde mixed with 5% eosin yellow in 10% formaldehyde was substituted for the malachite green solution used in the standard Kato-Katz method. This modification revealed the eggs of parasites like Schistosoma mansoni, Ascaris lumbricoides, Trichuris trichiura and hookworms distinctly. The slides made with this new technique could be accurately read within one hour. Faecal smears from 100 pupils in Kigungu, Entebbe, Uganda, were studied with both methods. The egg counts of S. mansoni, A. lumbricoides and T. trichiura by both methods were equal. The modified method, however, showed significantly higher hookworm egg counts (p < 0.001). Hookworm eggs were equal one hour after preparation of the slides as 16 hours after preparation. The intensity of infection detected was higher with the modified method for both S. mansoni and hookworms.