Regresar

Comparison of filtration staining (bell) and thick smear (kato) for the detection and quantitation of schistosoma mansoni eggs in faeces

Abstract:

We compare results of one Bell and one Kato-Katz examination performed on each of 315 stool specimens from residents in an area in north-eastern Brazil endemic for schistosomiasis mansoni. The prevalence of schistosome infection detected by the Bell technique was 76% and by the Kato-Katz technique was 63%. 81% of the infections missed by a Kato-Katz smear were light infections (one to 50 epg range by Bell examination). Over-all, 55% of stools in this egg count range by the Bell technique were negative on a single Kato-Katz smear. This implies that five Kato-Katz smears per stool would ensure a 95% probability (0·555 × 100) of detecting such light infections. However, a single Kato-Katz smear detected eggs in 97% of stools with a Bell count = 100 epg. For stools positive by both methods the egg counts per gram of stool were higher (p < 0·001) by Kato-Katz examination. Geometric mean egg counts for the infected population were 199 epg by the Kato-Katz and 92 epg by the Bell methods. 64% (59 v. 36) more persons were classified as heavily infected (= 400epg) by the Kato-Katz method than by the Bell method. The differing measurements of schistosome infection obtained with the Bell and Kato-Katz methods must be considered when comparing data on morbidity-infection relationships. © 1982 Oxford University Press.