# Precision mapping of schistosomiasis and soil-transmitted helminthiasis among school-age children: Targeting interventions in western Kenya

## TL;DR

This study maps schistosomiasis and soil-transmitted helminthiasis in western Kenya to better target treatments and reduce disease burden.

## Contribution

The study introduces a precision mapping protocol at the Ward level to improve targeting of interventions for parasitic infections.

## Key findings

- Precision mapping at the Ward level reduced the number of people treated for SCH and STH by 14.5% and 0.8%, respectively.
- Bungoma County had the highest S. mansoni prevalence (4.5%), while Trans Nzoia had the lowest (0.5%).
- STH infections were most common in Vihiga County (10.7%) and least in Trans Nzoia County (4.8%).

## Abstract

Mapping of schistosomiasis (SCH) and soil-transmitted helminthiasis (STH) is a critical step in understanding where at-risk populations live in order to effectively plan and target available resources and to achieve maximum impact on disease burden. A precision mapping protocol was developed and implemented in Kakamega, Bungoma, Trans Nzoia and Vihiga Counties in western Kenya by applying the current World Health Organization (WHO) mapping guideline at a lower administrative level (Ward).

Cross-sectional surveys were conducted among school-age children (SAC) in 5 primary schools purposefully selected in each mapping unit (Ward). In each school, stool and urine samples were collected from 60 randomly selected children (ages 8–14 years). The prevalence and intensity of infection of Schistosoma mansoni and STH were determined using the Kato-Katz technique and urine filtration for S. haematobium. Water Sanitation and Hygiene (WASH) status were also recorded.

Of the 46,464 children sampled, 3.2% (95% CI: 3.0-3.3) were infected with at least one Schistosoma species, with S. mansoni being the most predominant at 3.2% (95% CI: 2.9 - 3.3). 7.6% (95% CI: 7.3 – 7.8) of children were infected with at least one STH species, with A. lumbricoides being the most common (6.5%), and hookworm the least common (0.7%). The prevalence of S. mansoni was highest in Bungoma County (4.5%) and lowest in Trans Nzoia county (0.5%); STH prevalence was highest in Vihiga County (10.7%) and lowest in Trans Nzoia County (4.8%). SCH and STH infections were mainly of light intensity (2.2% and 5.6%, respectively). Based on sub-County-level data and prevalence threshold of ≥2% for MDA, 49 and 144 Wards required treatment for SCH and STH, respectively, whereas based on the Ward-level data, only 40 and 138 Wards required treatment for SCH and STH, respectively.

Use of Ward relative to sub-county prevalence revealed considerable spatial heterogeneity for SCH and STH and resulted in 14.5% and 0.8% reduction in the number of people treated for SCH and STH, respectively, underscoring the critical role of precision mapping in improved targeting of interventions.

Mapping schistosomiasis (SCH) and soil-transmitted helminthiasis (STH) is essential to identify at-risk populations and implement targeted interventions effectively. Despite global progress, existing SCH mapping approaches still struggle to account for SCH’s clustered distribution within implementation units. Since 2012, Kenya’s National School-Based Deworming Programme has focused on treating school-age children (SAC) based on a sub-national baseline survey and spatial modeling from that year. Under the Breaking Transmission Strategy (BTS), Kenya’s Ministry of Health adopted a WHO-guided Ward-level precision mapping protocol to support the elimination of neglected diseases like SCH and STH. This approach enabled a more accurate identification of at-risk populations, revealing variations in prevalence and ultimately reducing treatment needs for SCH and STH through more efficient community-based mass drug administration in western Kenya.