Prevalence and intensity of soil-transmitted helminth infections of children in sub-Saharan Africa, 2000-18: a geospatial analysis

Abstract

Background: Driven by global targets to eliminate soil-transmitted helminths as a public health problem, governments have rapidly rolled out control programmes using school and community-based platforms. To justify and target ongoing investment, quantification of impact and identification of remaining high-risk areas are needed. We aimed to assess regional progress towards these targets.

Methods: We did a continental-scale ecological analysis using a Bayesian space-time hierarchical model to estimate the effects of known environmental, socioeconomic, and control-related factors on the prevalence of soil-transmitted helminths, and we mapped the probability that implementation units had achieved moderate-to-heavy intensity infection prevalence of less than 2% among children aged 5-14 years between Jan 1, 2000, and Dec 31, 2018.

Findings: We incorporated data from 26 304 georeferenced surveys, spanning 3096 (60%) of the 5183 programmatic implementation units. Our findings suggest a reduction in the prevalence of soil-transmitted helminths in children aged 5-14 years in sub-Saharan Africa, from 44% in 2000 to 13% in 2018, driven by sustained delivery of preventive chemotherapy, improved sanitation, and economic development. Nevertheless, 1301 (25%) of 5183 implementation units still had an estimated prevalence of moderate-to-heavy intensity infection exceeding the 2% target threshold in 2018, largely concentrated in nine countries (in 1026 [79%] of 1301 implementation units): Nigeria, Democratic Republic of the Congo, Ethiopia, Cameroon, Angola, Mozambique, Madagascar, Equatorial Guinea, and Gabon.

Interpretation: Our estimates highlight the areas to target and strengthen interventions, and the areas where data gaps remain. If elimination of soil-transmitted helminths as a public health problem is to be achieved in sub-Saharan Africa by 2030, continued investment in treatment and prevention activities are essential to ensure that no areas are left behind.

Funding: Bill & Melinda Gates Foundation.

Figure 1

Prevalence of any soil-transmitted helminth infections (A) and of moderate-to-high intensity infections (B), and the absolute number of prevalent cases (C), in children aged 5–14 years in sub-Saharan Africa, 2000–18 Data are shown with 95% CIs. (A) Dotted lines with circle markers represent the raw aggregated prevalence in the underlying input data. (C) Blue bars represent any infections, and red bars represent moderate-to-high intensity infections.

Figure 2

Prevalence of any soil-transmitted helminth infection (A) and predominant soil-transmitted helminth species (B), by implementation unit, in 2000 and 2018 Predominant species was only assessed if the overall prevalence of soil-transmitted helminths was ≥2%.

Figure 3

Prevalence of moderate-to-heavy intensity infection with soil-transmitted helminths, by implementation unit, in 2018 (A), and probability that a given implementation unit had a prevalence of 2% of more (B)

Figure 4

Association between key indicators and the impact of interventions and development and prevalence of soil-transmitted helminth infections among children aged 5–14 years in sub-Saharan Africa, 2000–18 (A) Coefficients and 95% CIs for the multivariable risk factor analysis. (B) Time series of predicted population-weighted prevalence of soil-transmitted helminths for sub-Saharan Africa (blue line) and counterfactual predictions (red and black lines), assuming no effective mass drug administrations, changes in GDP PPP from baseline (2000), or improved sanitation coverage, by implementation unit. GDP PPP=gross domestic product at purchasing power parity.