Abstract
BackgroundKato-Katz technique has been the mainstay test in Schistosoma mansoni diagnosis in endemic areas. However, recent studies have documented its poor sensitivity in evaluating Schistosoma mansoni infection especially in areas with lower rates of transmission. It’s the primary diagnostic tool in monitoring impact of the Kenya national school based deworming program on infection transmission, but there is need to consider a more sensitive technique as the prevalence reduces. Therefore, this study explored the relationship between results of the stool-based Kato-Katz technique with urine-based point-of-care circulating cathodic antigen (POC-CCA) test in view to inform decision-making by the program in changing from Kato-Katz to POC-CCA test.MethodsWe used two cross-sectional surveys conducted pre- and post- mass drug administration (MDA) using praziquantel in a representative random sample of children from 18 schools across 11 counties. A total of 1944 children were randomly sampled for the study. Stool and urine samples were tested for S. mansoni infection using Kato-Katz and POC-CCA methods, respectively. S. mansoni prevalence using each technique was calculated and 95% confidence intervals obtained using binomial regression model. Specificity (Sp) and sensitivity (Sn) were determined using 2 × 2 contingency tables and compared using the McNemar’s chi-square test.ResultsA total of 1899 and 1878 children were surveyed at pre- and post-treatment respectively. S. mansoni infection prevalence was 26.5 and 21.4% during pre- and post-treatment respectively using POC-CCA test, and 4.9 and 1.5% for pre- and post-treatment respectively using Kato-Katz technique. Taking POC-CCA as the gold standard, Kato-Katz was found to have significantly lower sensitivity both at pre- and post-treatment, Sn = 12.5% and Sn = 5.2% respectively, McNemar test χ2m = 782.0, p < 0.001. In overall, the results showed a slight/poor agreement between the two methods, kappa index (k) = 0.11, p < 0.001, inter-rater agreement = 77.1%.ConclusionsResults showed POC-CCA technique as an effective, sensitive and accurate screening tool for Schistosoma mansoni infection in areas of low prevalence. It was up to 14-fold accurate than Kato-Katz which had extremely inadequate sensitivity. We recommend usage of POC-CCA alongside Kato-Katz examinations by Schistosomiasis control programs in low prevalence areas.
Highlights
Kato-Katz technique has been the mainstay test in Schistosoma mansoni diagnosis in endemic areas
We used simple random sampling technique to randomly sample 18 schools out of the 200 schools currently being followed by the monitoring and evaluation (M&E) programme, the included schools across 11 counties from Coastal, Rift Valley, Nyanza and Western regions of Kenya were based on their low S. mansoni prevalence of circa 10% at fourth year of that programme [22]
The number of children infected with S. mansoni as determined by point-of-care circulating cathodic antigen (POC-CCA) assay of one urine sample was found to be significantly higher than those determined by duplicate Kato-Katz thick smears of one stool sample and 5-fold higher during pre-treatment and 14-fold higher during posttreatment, this finding is in agreement with previous studies [1, 14, 30, 33, 34]
Summary
Kato-Katz technique has been the mainstay test in Schistosoma mansoni diagnosis in endemic areas. The Kato-Katz technique has showed day-today and intra-stool variability especially in areas with low intensity of infection and prevalence [5,6,7], with the cause of day-to-day variation believed to be biological [8], and the intra-stool variation attributed to sampling error due to the amount of stool evaluated [9] This has rendered the technique less useful especially in areas with lower rates of transmission with many studies projecting less true prevalence estimates from this technique as the population mean intensity of infection decreases [1, 10,11,12,13]. Programmes depending on single stool examination possibly lead to underestimated true infection prevalence with such observation resulting in an inaccurate allocation of control measures
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