The unreliability of the Kato‐Katz technique limits its usefulness for evaluating S. mansoni infections

Abstract

SummaryThe Kato-Katz technique, a (semi) quantitative stool examination technique, is generally recommended for diagnosis and evaluation of Schistosoma mansoni infection by schistosome experts. However, egg counts are subject to important variability. In order to quantify the reproducibility of egg counts using the Kato-Katz technique, ®eld data of 1255 observations on 299 subjects infected with Schistosoma mansoni were analysed. Agreement between repeated observations was assessed both categorically (kappa statistic) and continuously (analysis of variance). The day-to-day variation of egg counts was much greater than the variation due to different observers or different slides. The quantitative reproducibility was low: the weighted kappa statistic was 0.39 between specimens of different days, 0.62 between slides of the same specimen and 0.81 between observers of the same slide. Therefore the classi®cation of individual patients into groups based on egg counts, used as a measure of morbidity, must be interpreted with great care, especially in longitudinal studies. Usefulness of the Kato-Katz technique appears limited. Its reproducibility is low. It cannot be recommended as a routine test in a primary health care setting or in a hospital laboratory because safety and detection of other parasites are better assured by other techniques. It can be used in epidemiological studies and evaluation of schistosomiasis control programmes, but here too, other techniques might be preferred.keywords Kato-Katz technique, Schistoma mansoni, stool examination, reproducibility correspondence P. Van

Morbidity due to Schistosoma mansoni: an epidemiological assessment of distended abdomen syndrome in Ugandan school children with observations before and 1-year after anthelminthic chemotherapy

“…In contrast to urinary schistosomiasis where visual signs of morbidity are often apparent, such as gross haematuria, morbidity associated with intestinal schistosomiasis is often less obvious in all but the most severe or chronic cases (Kongs et al, 2001). Whilst clinical investigations with ultrasound and/or abdominal palpation methods can better describe morbidity associated with Schistosoma mansoni infection, for example hepatosplenomegaly, liver fibrosis and/or organ texture (Hatz, 2001;King et al, 2003), these require specialist equipment and well trained staff (Nooman et al, 1995;Ruiz et al, 2002).…”

Optimisation of a droplet digital PCR assay for the diagnosis of Schistosoma japonicum infection: A duplex approach with DNA binding dye chemistry

“…Moreover, currently, the diagnosis of schistosomiasis relies primarily on the direct microscopic detection of parasite ova, generally using the KK procedure, or by serology (Cai et al, 2014;WHO, 2013;Yu et al, 2007). While the KK is cheap and easy to implement, it can only detect patent infections and has relatively low sensitivity, particularly with light infections that occur in low disease transmission areas (Berhe et al, 2004;Kongs et al, 2001;Yu et al, 2007). In the case of S. japonicum, oviposition occurs 4-6 weeks post-infection and egg detection by microscopy can lack sensitivity due to variability in egg release and sampling related issues such as clumping of eggs and limited egg excretion in low intensity infections (Berhe et al, 2004;Kongs et al, 2001;Yu et al, 2007).…”

“…While the KK is cheap and easy to implement, it can only detect patent infections and has relatively low sensitivity, particularly with light infections that occur in low disease transmission areas (Berhe et al, 2004;Kongs et al, 2001;Yu et al, 2007). In the case of S. japonicum, oviposition occurs 4-6 weeks post-infection and egg detection by microscopy can lack sensitivity due to variability in egg release and sampling related issues such as clumping of eggs and limited egg excretion in low intensity infections (Berhe et al, 2004;Kongs et al, 2001;Yu et al, 2007). Serological techniques have low specificity and high cross reactivity, and cannot differentiate between an active and a past infection (Doenhoff et al, 2004;Xie et al, 2014).…”

“…Consequently, it is important to have available sensitive diagnostic tools that can detect low prevalence and low intensity infections, particularly within the framework of population surveillance and the monitoring of schistosomiasis control programs. Conventional parasitological diagnostic methods, such as the Kato-Katz (KK) thick smear examination or the miracidial hatching test (MHT), lack the requisite sensitivity in areas with low schistosome infection rates (Kongs et al, 2001;Spear et al, 2011;Yu et al, 2007).…”

Low transmission areas of schistosomiasis in Venezuela: consequences on the diagnosis, treatment, and control

“…In more recent studies and due to troublesome of the procedure and the numerous persons to be evaluated, only one sample was taken and two smears of that sample were examined by Kato-Katz. Although the examination of more samples of feces increase the probability of schistosomiasis diagnosis, the quantitative reproducibility of the Kato-Katz method has shown variations, especially when the amount of S. mansoni eggs is low (Kong et al 2001). Teesdale et al (1985) and Engels et al (1996) judge that due to the daily variation of the number of eggs, the analysis with two smears would be enough in order to increase the sensibility of the method.…”