Precision mapping of schistosomiasis and soil-transmitted helminthiasis among school age children at the coastal region, Kenya

Author summaryMapping of schistosomiasis (SCH) and soil-transmitted helminths (STH) is a critical step in understanding where at-risk populations live so as to plan and target available resources in order to achieve maximum impact on disease burden. While there has been progress in mapping of SCH across the world, the current mapping design for SCH is limited in addressing the focal nature of SCH in implementation units. As part of the Breaking Transmission Strategy (BTS) developed by the Kenyan Ministry of Health that focuses on elimination of neglected diseases including SCH and STH, an evaluation was conducted to identify the SCH and STH at-risk population to better target control using a precision mapping approach. The findings from this evaluation provided a comprehensive delineation of the distribution and prevalence of SCH and STH that informed the rollout of community-based mass drug administration for control of SCH and STH at the Kenyan coast. BackgroundAccurate mapping of schistosomiasis (SCH) and soil transmitted helminths (STH) is a prerequisite for effective implementation of the control and elimination interventions. A precision mapping protocol was developed and implemented in the coastal region of Kenya by applying the current World Health Organization (WHO) mapping guide at a much lower administrative level (ward). MethodsA two-stage cluster survey design was undertaken, with 5 villages in each ward selected. From within each village 50 households were randomly selected, and a single child between the ages of 8 and 14 sampled following appropriate assent. The prevalence and intensity of infection of Schistosoma mansoni and STH were determined using the Kato-Katz method (single stool, duplicate slides) and urine filtration for S. haematobium. ResultsOf the 27,850 school age children sampled, 6.9% were infected with at least one Schistosoma species, with S. haematobium being the most common 6.1% (95% CI: 3.1-11.9), and Tana River County having highest prevalence 19.6% (95% CI: 11.6-31.3). Prevalence of any STH infection was 5.8% (95% CI: 3.7-8.9), with Lamu County having the highest prevalence at 11.9% (95% CI: 10.0-14.1). The most prevalent STH species in the region was Trichuris trichiura at 3.1% (95% CI: 2.0-4.8). According to the WHO threshold for MDA implementation, 31 wards (in 15 sub-Counties) had a prevalence of >= 10% for SCH and thus qualify for annual MDA of all age groups from 2 years old. On the other hand, using the stricter Kenya BTS MDA threshold of >= 2%, 72 wards (in 17 sub-Counties) qualified for MDA and were targeted for treatment in 2021. ConclusionsThe precision mapping at the ward level demonstrated the variations of schistosomiasis prevalence and endemicity by ward even within the same sub-counties. The data collected will be utilized by the Kenyan Ministry of Health to improve targeting