School-based preventive chemotherapy program for schistosomiasis and soil-transmitted helminth control in Angola: 6-year impact assessment

BACKGROUND: A school preventive chemotherapy (PC) program for soil-transmitted helminths (STHs) and schistosomiasis has operated in Huambo, Uige and Zaire provinces, Angola, since 2013 and 2014, respectively; complemented by a school water, sanitation and hygiene (WASH) program in a subset of schools from 2016. Conducted in 2021, this is the first impact assessment of the school program for the control of schistosomiasis and STHs. METHODOLOGY/PRINCIPAL FINDINGS: A two-stage cluster design was used to select schools and schoolchildren for parasitological and WASH surveys. The rapid diagnostic tests (RDTs), point of care circulating cathodic antigen (POC-CCA) and Hemastix, were used to estimate Schistosoma mansoni and Schistosoma haematobium prevalence, respectively. Kato Katz was used to detect STHs, and quantify STH and S. mansoni infections. Urine filtration was used to quantify S. haematobium infections. Prevalence, infection intensity, relative prevalence reduction and egg reduction rates were calculated for schistosomiasis and STHs. Cohen’s Kappa co-efficient was used to assess agreement between RDTs and microscopy. Chi-square or Fisher’s exact test was used to compare WASH indicators in WASH-supported and WASH-unsupported schools. Overall, 17,880 schoolchildren (599 schools) and 6,461 schoolchildren (214 schools) participated in the schistosomiasis and STH surveys, respectively. Prevalence of any schistosomiasis in Huambo was 29.6%, Uige 35.4%, and Zaire 28.2%. Relative reduction in schistosomiasis prevalence from 2014 for Huambo was 18.8% (95% confidence interval (CI) 8.6, 29.0), Uige -92.3% (95%CI -162.2, -58.3), and Zaire -14.0% (95%CI -48.6, 20.6). Prevalence of any STH in Huambo was 16.3%, Uige 65.1%, and Zaire 28.2%. Relative reduction in STH prevalence for Huambo was -28.4% (95%CI -92.1, 35.2), Uige -10.7% (95%CI -30.2, 8.8), and Zaire -20.9% (95%CI -79.5, 37.8). A higher proportion of WASH-supported schools had improved water sources, and toilet and handwashing facilities compared to WASH-unsupported schools. CONCLUSIONS/SIGNIFICANCE: The limited impact this school program has had in controlling schistosomiasis and STHs identifies the need for a comprehensive understanding of individual, community, and environmental factors associated with transmission, and consideration for a community-wide control program.