Testing for soil-transmitted helminth transmission elimination: Analysing the impact of the sensitivity of different diagnostic tools.

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Title: Testing for soil-transmitted helminth transmission elimination: Analysing the impact of the sensitivity of different diagnostic tools.
Authors: Werkman, M
Wright, JE
Truscott, JE
Easton, AV
Oliveira, RG
Toor, J
Ower, A
Ásbjörnsdóttir, KH
Means, AR
Farrell, SH
Walson, JL
Anderson, RM
Item Type: Journal Article
Abstract: In recent years, an increased focus has been placed upon the possibility of the elimination of soil-transmitted helminth (STH) transmission using various interventions including mass drug administration. The primary diagnostic tool recommended by the WHO is the detection of STH eggs in stool using the Kato-Katz (KK) method. However, detecting infected individuals using this method becomes increasingly difficult as the intensity of infection decreases. Newer techniques, such as qPCR, have been shown to have greater sensitivity than KK, especially at low prevalence. However, the impact of using qPCR on elimination thresholds is yet to be investigated. In this paper, we aim to quantify how the sensitivity of these two diagnostic tools affects the optimal prevalence threshold at which to declare the interruption of transmission with a defined level of confidence. A stochastic, individual-based STH transmission model was used in this study to simulate the transmission dynamics of Ascaris and hookworm. Data from a Kenyan deworming study were used to parameterize the diagnostic model which was based on egg detection probabilities. The positive and negative predictive values (PPV and NPV) were calculated to assess the quality of any given threshold, with the optimal threshold value taken to be that at which both were maximised. The threshold prevalence of infection values for declaring elimination of Ascaris transmission were 6% and 12% for KK and qPCR respectively. For hookworm, these threshold values are lower at 0.5% and 2% respectively. Diagnostic tests with greater sensitivity are becoming increasingly important as we approach the elimination of STH transmission in some regions of the world. For declaring the elimination of transmission, using qPCR to diagnose STH infection results in the definition of a higher prevalence, than when KK is used.
Issue Date: 18-Jan-2018
Date of Acceptance: 14-Nov-2017
ISSN: 1935-2727
Publisher: Public Library of Science
Journal / Book Title: PLoS Neglected Tropical Diseases
Volume: 12
Issue: 1
Copyright Statement: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication
Keywords: 06 Biological Sciences
11 Medical And Health Sciences
Tropical Medicine
Publication Status: Published online
Open Access location:
Article Number: e0006114
Appears in Collections:Epidemiology, Public Health and Primary Care

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