Mapping Soil-Transmitted Helminth Infections of Children in Sub-Saharan Africa, 2000-2018

Background: Soil-transmitted helminths (STH) are among the most widespread neglected tropical diseases (NTDs) and infect over 1 billion people worldwide, with sub-Saharan Africa (SSA) accounting for >80% of disease burden. Driven by elimination targets, governments across SSA have rapidly rolled out control programmes using school and community based platforms. To justify and target ongoing investment in control, there is an urgent need to quantify their likely impact across SSA, and identify areas that remain at highest risk and unlikely to attain elimination thresholds. We examined the changes in STH prevalence amongst school-aged children in SSA from 2000 to 2018 at the programmatic implementation unit (IU) level to assess regional progress towards elimination.

Methods: We used quantitative survey data for Africa that consisted of 23,356 georeferenced survey data points from 2000-2018, and spanning 3,011 of the 5,183 programmatic IUs within the spatial extents of STH in SSA. The data were used within a joint multivariable Bayesian space-time hierarchical framework with covariates to estimate STH prevalence and intensity at IU level from 2000 to 2018.

Findings: Our findings suggest a steady decline in the prevalence of STH in SSA school-aged children, from 35% (or 74.6 million cases) in 2000 to 11% (or 33.9 million cases) in 2018, with the largest regional period decline for hookworm (23% to 5%), followed by Ascaris lumbricoides (14% to 7%) and Trichuris trichiura (5% to 2%), with convergence of hookworm and A. lumbricoides levels in 2013. By 2018, approximately 37% (1,938 of 5,183) of IU’s in SSA still had an estimated prevalence of moderate-to-heavy intensity infection exceeding the 1% target threshold, largely concentrated in five countries: Democratic Republic of Congo, Ethiopia, Nigeria, Mozambique and Cameroon. The strongest factors driving reductions in prevalence were sustained effective preventative chemotherapy treatments, followed by improved sanitation, and lastly economic development.

Interpretation: Our estimates provide an important tool for identifying where to target and further strengthen interventions, and where data gaps remain. If elimination of STH as a public health problem is to be achieved in SSA by 2030, renewed and increased investment in STH treatment and prevention activities are urgently required to accelerate reductions and ensure that no areas are left behind.