Evaluating the Performance of Diagnostic methods for soil transmitted helminths in the Amhara National Regional State, Northwest Ethiopia

Fenta, Abebe; Hailu, Tadesse; Alemu, Megbaru; Nibret, Endalkachew; Amor, Arancha; Munshea, Abaineh

doi:10.21203/rs.3.rs-30993/v3

Cited by 3 publications

(3 citation statements)

References 29 publications

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“…Second, we suggest a re-appraisal of the value of the current diagnostic standards. For example, a single Kato-Katz thick smear is the current diagnostic standard for STHs, and although it lacks sensitivity to detect infections of low intensity ([ 13 , 14 , 28 , 29 ]: Ascaris : ~55%, Trichuris : ~80%, hookworms: ~70%), it has a high specificity (≥98%) [ 19 , 30 ]. In other words, this cheap and simple method might still be valuable at the program’s endgame, though the survey design will need to be adapted accordingly.…”

Section: Discussionmentioning

confidence: 99%

Two-stage lot quality assurance sampling framework for monitoring and evaluation of neglected tropical diseases, allowing for imperfect diagnostics and spatial heterogeneity

2022

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Background Monitoring and evaluation (M&E) is a key component of large-scale neglected tropical disease (NTDs) control programs. Diagnostic tests deployed in these M&E surveys are often imperfect, and it remains unclear how this affects the population-based program decision-making. Methodology We developed a 2-stage lot quality assurance sampling (LQAS) framework for decision-making that allows for both imperfect diagnostics and spatial heterogeneity of infections. We applied the framework to M&E of soil-transmitted helminth control programs as a case study. For this, we explored the impact of the diagnostic performance (sensitivity and specificity), spatial heterogeneity (intra-cluster correlation), and survey design on program decision-making around the prevalence decisions thresholds recommended by WHO (2%, 10%, 20% and 50%) and the associated total survey costs. Principal findings The survey design currently recommended by WHO (5 clusters and 50 subjects per cluster) may lead to incorrect program decisions around the 2% and 10% prevalence thresholds, even when perfect diagnostic tests are deployed. To reduce the risk of incorrect decisions around the 2% prevalence threshold, including more clusters (≥10) and deploying highly specific diagnostic methods (≥98%) are the most-cost saving strategies when spatial heterogeneity is moderate-to-high (intra-cluster correlation >0.017). The higher cost and lower throughput of improved diagnostic tests are compensated by lower required sample sizes, though only when the cost per test is <6.50 US$ and sample throughput is ≥3 per hour. Conclusion/Significance Our framework provides a means to assess and update M&E guidelines and guide product development choices for NTDs. Using soil-transmitted helminths as a case study, we show that current M&E guidelines may severely fall short, particularly in low-endemic and post-control settings. Furthermore, specificity rather than sensitivity is a critical parameter to consider. When the geographical distribution of an NTD within a district is highly heterogeneous, sampling of more clusters (≥10) may be required.

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Section: Discussionmentioning

confidence: 99%

Two-stage lot quality assurance sampling framework for monitoring and evaluation of neglected tropical diseases, allowing for imperfect diagnostics and spatial heterogeneity

2022

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“…For this study, we expanded this framework to also capture variation in intensity of infection across STH species (Ascaris lumbricoides, Trichuris trichiura, hookworms), across schools, between and within individuals, and between repeated thick smears. These sources of variation are important as the sensitivity of KK for detecting infection in an individual depends on the intensity of infection [8][9][10][11][12]. Furthermore, using this expanded framework, we assess to what extent the accuracy of survey results can be improved (and at what cost) by increasing the number of thick smears per stool sample or the number of stool samples per person [8,13].…”

Section: Introductionmentioning

confidence: 99%

A general framework to support cost-efficient survey design choices for the control of soil-transmitted helminths when deploying Kato-Katz thick smear

et al. 2023

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Background To monitor and evaluate soil-transmitted helminth (STH) control programs, the World Health Organization (WHO) recommends screening stools from 250 children, deploying Kato-Katz thick smear (KK). However, it remains unclear whether these recommendations are sufficient to make adequate decisions about stopping preventive chemotherapy (PC) (prevalence of infection <2%) or declaring elimination of STH as a public health problem (prevalence of moderate-to-heavy intensity (MHI) infections <2%). Methodology We developed a simulation framework to determine the effectiveness and cost of survey designs for decision-making in STH control programs, capturing the operational resources to perform surveys, the variation in egg counts across STH species, across schools, between and within individuals, and between repeated smears. Using this framework and a lot quality assurance sampling approach, we determined the most cost-efficient survey designs (number of schools, subjects, stool samples per subject, and smears per stool sample) for decision-making. Principal findings For all species, employing duplicate KK (sampling 4 to 6 schools and 64 to 70 subjects per school) was the most cost-efficient survey design to assess whether prevalence of any infection intensity was above or under 2%. For prevalence of MHI infections, single KK was the most cost-efficient (sampling 11 to 25 schools and 52 to 84 children per school). Conclusions/Significance KK is valuable for monitoring and evaluation of STH control programs, though we recommend deploying a duplicate KK on a single stool sample to stop PC, and a single KK to declare the elimination of STH as a public health problem.

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“…These sources of variation are important as the sensitivity of KK for detecting infection in an individual depends on the intensity of infection [5][6][7][8][9]. Furthermore, using this expanded framework, we assess to what extent the accuracy of survey results can be improved (and at what cost) by increasing the number of thick smears per stool sample or the number of stool samples per person [5,10].…”

Section: Introductionmentioning

confidence: 99%

A general framework to support cost-efficient survey design choices for the control of soil-transmitted helminths when deploying Kato-Katz thick smear

Levecke

Leta

Vlas

et al. 2023

Preprint

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Background To monitor and evaluate soil-transmitted helminth (STH) control programs, the World Health Organization (WHO) recommends screening stools from 250 children across 5 schools, deploying Kato-Katz thick smear (KK). However, it remains unclear whether these recommendations are sufficient to make adequate decisions about stopping preventive chemotherapy (PC) (prevalence of infection <2%) or declaring elimination of STH as a public health problem (prevalence of moderate-to-heavy intensity (MHI) infections <2%). Methodology We developed a simulation framework to determine the effectiveness and cost of survey designs for decision-making in STH control programs, capturing the operational resources to perform surveys, the variation in egg counts across STH species, across schools, between and within individuals, and between repeated smears. Using this framework and a lot quality assurance sampling approach, we determined the most cost-efficient survey designs (number of schools, subjects, stool samples per subject, and smears per stool sample) for decision-making. Principal findings For all species, employing duplicate KK (sampling 4 to 6 schools and 64 to 70 subjects per school) was the most cost-efficient survey design to assess whether prevalence of any infection intensity was above or under 2%. For prevalence of MHI infections, single KK was the most cost-efficient (sampling 11 to 25 schools and 52 to 84 children per school). Conclusions/Significance KK is valuable for monitoring and evaluation of STH control programs, though we recommend to deploy a duplicate KK on a single stool sample to stop PC, and a single KK to declare the elimination of STH as a public health problem.

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Evaluating the Performance of Diagnostic methods for soil transmitted helminths in the Amhara National Regional State, Northwest Ethiopia

Cited by 3 publications

References 29 publications

Two-stage lot quality assurance sampling framework for monitoring and evaluation of neglected tropical diseases, allowing for imperfect diagnostics and spatial heterogeneity

Two-stage lot quality assurance sampling framework for monitoring and evaluation of neglected tropical diseases, allowing for imperfect diagnostics and spatial heterogeneity

A general framework to support cost-efficient survey design choices for the control of soil-transmitted helminths when deploying Kato-Katz thick smear

A general framework to support cost-efficient survey design choices for the control of soil-transmitted helminths when deploying Kato-Katz thick smear

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