Soil-transmitted helminth (STH) infections in the Wolaita zone in Southern Ethiopia. Mid-stage evaluation of the Geshiyaro project and progress towards the interruption of transmission

Abstract Background This paper documents changes in the prevalence and intensity of Soil-Transmitted helminths (STH) infections in the Geshiyaro project in the Woliata zone of Southern Ethiopia. Method The Geshiyaro project comprises three intervention arms. Arm 1 is sub-divided into “Arm 1 pilot” (one district), and Arm 1 (four other districts), both receiving integrated community-wide MDA with intensive WaSH interventions. Arm 2 involves 18 districts with community-wide MDA interventions plus the existing government- led “One-WaSH” programme, while Arm 3 serves as a control with school-based MDA interventions plus the existing government-led “One-WaSH” programme in three districts. A total of 45 longitudinal parasitological surveillance sentinel sites are being used across all three intervention arms to monitor STH prevalence. From each of the 45 sentinel sites, 150 individuals were randomly selected, stratified by age and gender. T-tests and ANOVA were employed to compare infection prevalence and intensity across the three study arms. Results The prevalence of STH decreased significantly 34.5% (30.6%, 38.5) in 2019 to 10.6% (8.3%, 13.4%) in 2022/2023 (df=1, p<0.0001) in Arm 1 pilot, from 27.4% (25.2%, 29.7%) in 2020 to 5.5% (4.4%, 6.7%) in 2023 (df=1, p<0.0001) in Arm 1, from 23% (21.3%, 24.8%) in 2020 to 4.5% (3.7%, 5.3%) in 2023 (df=1, p<0.001) in Arm 2, from 49.6% (47.4%, 51.7%) in 2021 to 26.1% in 2023 (df=1, p<0.0001) in Arm 3. The relative reduction in the prevalence of any STH was the highest in the Arms employing community wide MDA; namely, Arm 2, with a decrease of 82.5% (79.3%, 84.2%), followed by Arm 1 with a reduction of 80.1% (75.3%, 84.6%), then Arm 1 pilot with a decrease of 69.4% (60.1%. 76.6%). Arm 3 employing school-based MDA had the lowest decrease with a reduction of 46.9% (43.6%, 51%). The mean intensity of infection (based on Kato Katz egg count measures) for Ascarisspecies which was the dominant STH species present in the study area decreased significantly in Arms 1 and 2, but only slightly in Arm 3. The prevalence of hookworm and Trichuris infections were found to be relatively small in all arms and decreased significantly. Conclusion The reduction in prevalence and intensity in Arms 1 and 2 revealed steady progress towards transmission interruption based on community-wide MDA intervention but additional efforts are required to achieve a 2% prevalence threshold by qPCR.