Comparing the Performance of Cluster Random Sampling and Integrated Threshold Mapping for Targeting Trachoma Control, Using Computer Simulation

Abstract

BackgroundImplementation of trachoma control strategies requires reliable district-level estimates of trachomatous inflammation–follicular (TF), generally collected using the recommended gold-standard cluster randomized surveys (CRS). Integrated Threshold Mapping (ITM) has been proposed as an integrated and cost-effective means of rapidly surveying trachoma in order to classify districts according to treatment thresholds. ITM differs from CRS in a number of important ways, including the use of a school-based sampling platform for children aged 1–9 and a different age distribution of participants. This study uses computerised sampling simulations to compare the performance of these survey designs and evaluate the impact of varying key parameters.Methodology/Principal FindingsRealistic pseudo gold standard data for 100 districts were generated that maintained the relative risk of disease between important sub-groups and incorporated empirical estimates of disease clustering at the household, village and district level. To simulate the different sampling approaches, 20 clusters were selected from each district, with individuals sampled according to the protocol for ITM and CRS. Results showed that ITM generally under-estimated the true prevalence of TF over a range of epidemiological settings and introduced more district misclassification according to treatment thresholds than did CRS. However, the extent of underestimation and resulting misclassification was found to be dependent on three main factors: (i) the district prevalence of TF; (ii) the relative risk of TF between enrolled and non-enrolled children within clusters; and (iii) the enrollment rate in schools.Conclusions/SignificanceAlthough in some contexts the two methodologies may be equivalent, ITM can introduce a bias-dependent shift as prevalence of TF increases, resulting in a greater risk of misclassification around treatment thresholds. In addition to strengthening the evidence base around choice of trachoma survey methodologies, this study illustrates the use of a simulated approach in addressing operational research questions for trachoma but also other NTDs.

Factors Associated with the Performance and Cost-Effectiveness of Using Lymphatic Filariasis Transmission Assessment Surveys for Monitoring Soil-Transmitted Helminths: A Case Study in Kenya

“…Random effect values were then predicted for each school using a process termed conditional simulation, which uses semivariogram parameters to spatially predict random effect values for each prediction school. One thousand conditional simulations were conducted to generate 1,000 equally probable and spatially realistic “realizations” of possible random effect values at all schools 10,19,20. These random effect values were added to the fixed effect predictions and back transformed from log odds to generate age-specific prevalence values.…”

Prevalence of Trachoma in Pakistan: Results of 42 Population-Based Prevalence Surveys from the Global Trachoma Mapping Project

“…13,14 In order to plan and implement SAFE interventions, population-based prevalence surveys of TF and trichiasis are needed in districts suspected to be trachoma-endemic. 15,16 Public health-level implementation of S is indicated in districts where trachomatous trichiasis prevalence is ≥0.2% in persons aged ≥15 years, while public health-level implementation of A, F and E is indicated in districts where TF prevalence is ≥5% in children aged 1-9 years. 17 In Pakistan in the 1950s, trachoma was believed to account for >60% of all blindness nationally.…”

Prevalence of trachoma in Yemen: results of population-based prevalence surveys of 42 evaluation units in nine governorates

“…4 To achieve this goal, WHO recommends the SAFE strategy (surgery, antibiotics, facial cleanliness, and environmental improvement) 5 in all areas where trachoma prevalence exceeds elimination thresholds, based on population-based surveys. [6][7][8] Data on the prevalence of trichiasis in adults, the blinding stage of disease, are used to plan surgical interventions; data on the prevalence of trachomatous inflammation-follicular (TF) in 1-9-year-olds are used for planning antibiotic, facial cleanliness, and environmental improvement interventions. 9,10 The Republic of Yemen is located on the Arabian Peninsula, bordered on the north and east by Saudi Arabia and Oman respectively, and on the south and west by the Arabian Sea, the Gulf of Aden, and the Red Sea.…”