Abstract
Soil transmitted helminth (STH) infections are among the most common human infections worldwide with over 1 billion people affected. Many estimates of STH infection are often based on school-aged children (SAC). This study produced predictive risk-maps of STH on a more finite scale, estimated the number of people infected, and the amount of drug required for preventive chemotherapy (PC) in Ogun state, Nigeria. Georeferenced STH infection data obtained from a cross-sectional survey at 33 locations between July 2016 and November 2018, together with remotely-sensed environmental and socio-economic data were analyzed using Bayesian geostatistical modelling. Stepwise variable selection procedure was employed to select a parsimonious set of predictors to predict risk and spatial distribution of STH infections. The number of persons (pre-school ages children, SAC and adults) infected with STH were estimated, with the amount of tablets needed for preventive chemotherapy. An overall prevalence of 17.2% (95% CI 14.9, 19.5) was recorded for any STH infection. Ascaris lumbricoides infections was the most predominant, with an overall prevalence of 13.6% (95% CI 11.5, 15.7), while Hookworm and Trichuris trichiura had overall prevalence of 4.6% (95% CI 3.3, 5.9) and 1.7% (95% CI 0.9, 2.4), respectively. The model-based prevalence predictions ranged from 5.0 to 23.8% for Ascaris lumbricoides, from 2.0 to 14.5% for hookworms, and from 0.1 to 5.7% for Trichuris trichiura across the implementation units. The predictive maps revealed a spatial pattern of high risk in the central, western and on the border of Republic of Benin. The model identified soil pH, soil moisture and elevation as the main predictors of infection for A. lumbricoides, Hookworms and T. trichiura respectively. About 50% (10/20) of the implementation units require biannual rounds of mass drug administration. Approximately, a total of 1.1 million persons were infected and require 7.8 million doses. However, a sub-total of 375,374 SAC were estimated to be infected, requiring 2.7 million doses. Our predictive risk maps and estimated PC needs provide useful information for the elimination of STH, either for resource acquisition or identifying priority areas for delivery of interventions in Ogun State, Nigeria.
Highlights
Soil transmitted helminth (STH) infections are among the most common human infections worldwide with over 1 billion people affected
The aims of this study were (1) to map and predict the spatial distribution of soil-transmitted helminth infections at 2 km spatial scale using a Bayesian geostatistical approach; (2) identify the most important climatic, environmental and socioeconomic determinants of soil-transmitted helminth infections (3) calculate the number of persons infected and; (4) estimate the annual drug requirements for preventive chemotherapy according to guidelines put forward by the World Health Organization (WHO)
Ascaris lumbricoides infections was the most predominant, with an overall prevalence of 13.6%, while Hookworm and Trichuris trichiura had overall prevalence of 4.6% and 1.7%, respectively
Summary
Soil transmitted helminth (STH) infections are among the most common human infections worldwide with over 1 billion people affected. SAC School-aged children GIS Geographic information system RS Remote sensing IU Implementation units LGAs Local government areas SAF Sodium acetate acetic acid formaldehyde NDVI Normalized difference vegetation index EVI Enhanced vegetation index LSTD Land surface temperature for day LSTN Land surface temperature for night MDA Mass drug administration NLE Night light emission MODIS/TERRA Moderate resolution imaging spectroradiometer C3S Corpernicus climate change service WORLDPOP World population database LBD Local Burden of Disease Project AIC Akaike information criterion GMRF Gaussian Markov random field INLA Integrated nested Laplace approximation SPDE Stochastic partial differential equation CI Confidence interval OR Odd ratio BCI Bayesian credible interval. A total of 576 million (59.9%) of the estimated 1.1 billion children requiring albendazole or mebendazole medicines were treated in 2018, and about 71.3% of the implementation units (IUs) achieved the 75% effective coverage target for SAC12,13. The recently published 2020–2030 NTD road map, emphasized more specific targets by 2030 which includes (1) eliminating STH as a public health problem (< 2% proportion of moderate and heavy intensity infections) in 96 countries; (2) reducing by 50% the number of tablets required during PC for STH and (3) increasing domestic financial support for PC for STH, with 25 countries deworming children using domestic funds[12,14,15]
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