Wastewater-based epidemiological study on helminth egg detection in untreated sewage sludge from Brazilian regions with unequal income.

Background: Helminthiases are neglected diseases that affect billions of people worldwide, particularly those with inadequate sanitation, poor hygiene practices, and limited access to clean water. Due to frequent underreporting, wastewater-based epidemiology has emerged as a valuable tool for monitoring parasitic infections at population-level. This study aimed to detect and quantify helminth eggs in untreated sewage sludge from eight wastewater treatment plants located in different Brazilian socioeconomic regions.

Methods: The study was conducted from June 2021 to December 2023 in Goiás and Federal District, the Brazilian federative unit with the highest income inequality. Samples were collected bimonthly (n = 121). Helminth eggs were recovered using centrifugation and flotation with a ZnSO solution (d = 1.30 g/ml). After 21-28 days of incubation in sulfuric acid, viable eggs were identified and counted using a Sedgewick-Rafter Chamber under an optical microscope. Statistical analyses included One-way analysis of variance (ANOVA) followed by Tukey's multiple comparisons test to evaluate differences in helminth egg counts between low-, medium- and high-income regions.

Results: Twelve helminth genera were identified, revealing significant differences in prevalence and diversity across socioeconomic strata. Cestode eggs, particularly Hymenolepis spp. (44.28%), were the most prevalent overall. Trematode eggs were less frequent but exhibited greater taxonomic diversity. Sludge from low-income areas had the highest egg concentration [16.61 ± 3.02 eggs per gram of dry mass ( eggs/g DM)], nearly five times greater than in high-income areas such as Brasília Norte (3.56 ± 0.55 eggs/g DM; P = 8.8 × 10⁻⁹). Ascaris spp. (19.27%) and Trichuris spp. (7.90%) predominated in low-income areas. Medium-income regions showed intermediate values, with notable regional variation.

Conclusions: Our results demonstrate that helminth egg diversity and concentration in sewage sludge are closely related to the socioeconomic characteristics of the served population. These findings may inform prevention and control strategies in vulnerable areas and support the development of public health and sanitation policies that address social and environmental inequalities in Brazil's Central-Western region.