Prevalence, intensity and risk factors of soil-transmitted helminthiasis after five effective rounds of preventive chemotherapy across three implementation units in Ondo State, Nigeria
Authors: Mogaji Hammed O. , Olamiju Francisca O. , Oyinlola Fajana , Achu Ijeoma , Adekunle Nimota O. , Udofia Lydia E. , Edelduok Ekaette G. , Yaro Clement A. , Oladipupo Olanike O. , Kehinde Alice Y. , Oyediran Fatai , Aderogba Moses , Makau-Barasa Louise K. , Ekpo Uwem F. 
Published: September 2024

Background

Routine epidemiological data are essential for monitoring the effectiveness of preventive chemotherapy (PC), optimizing resource allocation, and addressing the evolving needs in the elimination of soil-transmitted helminthiasis (STH). This study assesses the prevalence, intensity, and associated risk factors of STH following five rounds of albendazole-based PC in three implementation units (IUs) in Ondo State, Nigeria.

Methodology

Fresh stool samples were collected from 2,093 children aged 5–14 years across 45 systematically selected schools in three IUs: Ese-Odo, Irele, and Ile-Oluji. The samples were analyzed using the Kato-Katz technique. Additionally, standardized questionnaires were administered to gather data on demographics and access to water, sanitation, and hygiene (WASH) resources. Data analysis was conducted using R software version 4.3.2, with a 95% confidence interval.

Principal Findings/Conclusions

The parasitological data indicated a significant decline in the aggregated prevalence of STH across the three IUs. In Ese-Odo, the prevalence decreased to 25.8% (95% CI: 23.0–29.0) from 39% at baseline (d = -34%, p = 0.00). In Irele, prevalence dropped to 9.7% (95% CI: 7.6–12.0) from 51.3% at baseline (d = -81%, p = 0.00), and in Ile-Oluji, prevalence was reduced to 6.4% (95% CI: 4.6–8.7) from 23% at baseline (d = -72.2%, p = 0.00). The most prevalent STH species wasAscaris lumbricoides, with infection rates of 25.5%, 9.4%, and 6.4% in Ese-Odo, Irele, and Ile-Oluji, respectively, followed byTrichuris trichiurain Ese-Odo (2.7%) and Irele (0.4%), while hookworm infections were detected only in Irele (0.7%). The majority of infections were of low intensity in Ese-Odo (91.0%), Irele (96.8%), and Ile-Oluji (100%). Access to improved sanitation (17.7%, 54.9%, and 58.2%, p < 0.05), improved water sources (24.5%, 66.1%, and 69.8%, p < 0.05), and handwashing facilities (9.0%, 39.6%, and 25.4%) was suboptimal across Ese-Odo, Irele, and Ile-Oluji, respectively. Open defecation rates were high in Ese-Odo (54.2%), Irele (36.3%), and Ile-Oluji (34.3%). In Ese-Odo, significant risk factors for STH infection included the use of hand-pump boreholes (AOR: 2.44, 95% CI: 1.23–4.88, p = 0.01), unprotected dug wells (AOR: 3.25, 95% CI: 0.96–11.36, p = 0.06), ventilated improved pit latrines (AOR: 3.95, 95% CI: 1.13–16.1, p = 0.04), pit latrines without a slab (AOR: 2.19, 95% CI: 1.27–3.8, p = 0.01), and failure to use soap after defecation, both when soap was available (AOR: 12.09, 95% CI: 1.86–112.97, p = 0.01) and when soap was unavailable (AOR: 8.19, 95% CI: 1.73–76.65, p = 0.04). In Irele, access to protected dug wells was marginally significant (AOR: 1.79, 95% CI: 0.96–3.21, p = 0.06), while in Ile-Oluji, access to river water emerged as a significant risk factor (AOR: 7.97, 95% CI: 1.81–58.58, p = 0.02). The use of rainwater was found to be protective across all three IUs. These findings demonstrate significant progress in reducing STH prevalence across the three IUs following PC interventions. However, the data underscore the need for enhanced efforts to improve access to and use of WASH facilities to achieve STH elimination.

Authors Summary

The World Health Organization (WHO) recommends reducing soil-transmitted helminthiasis (STH) prevalence to below 20% and moderate-to-heavy infections to less than 2% in treated areas to achieve elimination targets. Endemic countries, including Nigeria, have implemented mass albendazole administration to at-risk populations to meet these goals. After a decade of such interventions in Nigeria, reassessing the infection status is essential for determining whether to adjust or discontinue the program. This study analyzed stool samples from 2,093 children across three implementation units (IUs) in Ondo State. The results indicated significant reductions in STH prevalence to below 20% in two of the three IUs, with no heavy infections reported in any IU. While these findings demonstrate the effectiveness of the PC interventions, the study also identified poor access to water, sanitation, and hygiene (WASH) resources, highlighting the need for improvements in these areas to sustain progress and prevent infection resurgence.