Effect of sanitation improvements on soil-transmitted helminth eggs in courtyard soil from rural Bangladesh: Evidence from a cluster-randomized controlled trial

Abstract

Improved sanitation has been hypothesized to reduce soil-transmitted helminth (STH) infections by reducing the prevalence and abundance of STH eggs/larvae in soil. We evaluated the effect of a randomized sanitation program (providing households with an improved dual-pit latrine, tools for child/animal feces management, and behavioral messaging) on reducing STH eggs in soil from household courtyards. We collected soil samples from 1405 households enrolled in the sanitation intervention (n=419) and control (n=914) groups of a cluster-randomized controlled trial (WASH Benefits) in rural Bangladesh approximately 2 years after the initiation of the interventions. We analyzed samples for Ascaris lumbricoides, Trichuris trichiura, and hookworm eggs by microscopy. We estimated prevalence ratios (PR) and relative egg count reductions (ECR) to compare the prevalence of any STH eggs and arithmetic and geometric mean egg counts for any STH per gram of soil between the sanitation and control arms.Among intervention households, latrines achieved high and sustained user uptake by adults while child open defecation remained common and most households did not dispose of child feces hygienically. In courtyard soil from control households, the prevalence of any STH eggs was 75.7% and the prevalence of any larvated STH eggs was 67.3%. A. lumbricoides was detected in 63.0% of control samples and T. trichiura in 55.7% of control samples; hookworm was not detected in any sample. The arithmetic mean egg count for any STH was 3.96 eggs/dry gram, while the geometric mean was 1.58 eggs/dry gram. There was no difference between the intervention and control groups in the prevalence of any STH eggs (PR=0.98 (95% CI: 0.91–1.05)) or mean egg counts (ECR=0.08 (95% CI: −0.10, 0.26) for geometric mean and 0.07 (95% CI: −0.22, 0.37) for arithmetic mean). Adjusted models gave similar results.A compound-level sanitation intervention that provided improved latrines and tools for disposal of child and animal feces did not have an impact on environmental reservoirs of STH eggs. In order to effectively reduce the prevalence and abundance of STH eggs in the environment, sustained, widespread use of sanitation strategies to isolate and hygienically dispose of child and animal feces may need to complement traditional strategies for containment of adult human feces.Author summaryImproved sanitation has been hypothesized to reduce soil-transmitted helminth (STH) infections by reducing the prevalence and abundance of STH eggs/larvae in soil. We evaluated the effect of a randomized sanitation program (providing households with an improved dual-pit latrine, tools for child/animal feces management, and behavioral messaging) on reducing STH eggs in soil from household courtyards. We collected soil samples from 1405 households enrolled in the control and sanitation groups of a cluster-randomized controlled trial (WASH Benefits) in rural Bangladesh approximately 2 years after the initiation of the interventions. We analyzed samples for Ascaris lumbricoides, Trichuris trichiura and hookworm eggs by microscopy. We found no effect of the sanitation intervention on STH eggs in soil. In order to effectively reduce the prevalence and abundance of STH eggs in the environment, sustained, widespread use of sanitation strategies to isolate and hygienically dispose of child and animal feces may need to complement traditional strategies for containment of adult human feces.

Persistent Ascaris Transmission Is Possible in Urban Areas Even Where Sanitation Coverage Is High

“…Foundational to helminth control efforts is mass drug administration (MDA), but in endemic settings, MDA is a short-term treatment strategy that should be accompanied by improvements to sanitation, hygiene, and housing to break the cycle of infection. 81,82 However, onsite sanitation interventions have not demonstrated substantial reductions in environmental fecal contamination, 13,83,84 and this work suggests that even nearly universal coverage of these systems alone may be…”

“…In highly endemic settings, this indicates that nearly all fecal wastes must be safely sequestered because even small releases to the environment could allow the cycle of infection to continue. Foundational to helminth control efforts is mass drug administration (MDA), but in endemic settings, MDA is a short-term treatment strategy that should be accompanied by improvements to sanitation, hygiene, and housing to break the cycle of infection. , However, onsite sanitation interventions have not demonstrated substantial reductions in environmental fecal contamination, ,, and this work suggests that even nearly universal coverage of these systems alone may be insufficient to interrupt Ascaris transmission in endemic settings. Instead, a sustainable environmental response to the risks posed by helminths and other fecal-oral pathogens will require policies and strategies capable of achieving a nearly complete reduction in the child feces and fecal sludges transported to the living environment.…”