Effect of environmental factors in reducing the prevalence of schistosomiasis in schoolchildren: A panel analysis of three extensive national prevalence surveys in Brazil (1950–2018)
Authors: Santos Mariana Cristina Silva , de Oliveira Guilherme Lopes , Mingoti Sueli Aparecida , Heller Léo 
Published: September 2022

Background

Over seven decades, Brazil has made admirable progress in controlling schistosomiasis, and a frequent question about the explanation for this reduction refers to the effect of improving environmental factors in the country. This article seeks to identify factors related to the change in the epidemiological situation of schistosomiasis mansoni infection by analyzing three national prevalence surveys conducted since 1950.

Methodology/principal findings

This is an ecological study analyzing an unbalanced panel of data based on national surveys and considering the municipality as the unit of analysis. The sample consisted of 1,721 Brazilian municipalities, in which a total of 1,182,339 schoolchildren aged 7–14 was examined during the three periods corresponding to each survey (1947–1952, 1975–1979, and 2011–2015). Zero-inflated Poisson regression models, with mixed and random effects, were adjusted to assess the association between candidate factors and disease prevalence using a significance level of 5%. There was a significant decrease in disease prevalence between the first and last periods analyzed (RR 0.214, CI 0.184 – 0.249), with a protective association with access to sanitation (RR 0.996, CI 0.994 – 0.998), urbanization (RR 0.991, CI 0.989 – 0.993), and living in own households (RR 0.986, CI 0.983 – 0.989); and an inverse association with the water supply (RR 1.010, CI 1.008 – 1.011).

Conclusion

The findings of this study indicate a decrease in the prevalence of schistosomiasis over seven decades in schoolchildren from the analyzed Brazilian municipalities, mediated by environmental factors and social conditions. The increased access to piped water in the municipalities apparently triggers other ways of contact with watercourses, generating new transmission routes and suggesting the need for a systemic approach concerning contact with water.

Author Summary

Schistosomiasis mansoni is a neglected tropical disease caused by infection from parasitic worms of the speciesSchistosoma mansoni. Due to the complexity of the mechanism of transmission and maintenance of schistosomiasis, several preventive actions on diverse conditioning factors can promote disease control. Active search, timely treatment of cases, stool tests, and epidemiological investigations are the initial actions under programs for epidemiological surveillance of the disease. Thus, momentum historical landmark surveys on the national prevalence of the disease can provide valuable information about its epidemiological pattern over the years. Our study addressed three national surveys with historical coverage (1950, 1970, and 2010) that mapped the prevalence of the disease in children aged 7–14 for nearly seven decades. We also employed statistical models to investigate which environmental, economic, or demographic factors are associated with the disease in several municipalities. The results showed that the decrease in schistosomiasis from the 1950s to the 2010s was statistically significant, suggesting that improvements in water supply and sanitation conditions require structured and systemic approaches for controlling new forms of disease transmission and outbreak.