Effects of water quality, sanitation, handwashing and nutritional interventions on enteric pathogen seroconversion in rural Kenya: a cluster randomised trial

Technical Summary: Effects of Water Quality, Sanitation, Handwashing, and Nutritional Interventions on Enteric Pathogen Seroconversion in Rural Kenya

Problem and Background
Enteric pathogens remain a primary cause of child morbidity and mortality in low-resource settings, contributing to malnutrition, growth faltering, and impaired neurodevelopment. While clinical diarrhea is a common metric, subclinical infections are also prevalent and harmful. Prevention strategies typically rely on Water, Sanitation, and Handwashing (WASH) interventions and nutritional support. However, large-scale efficacy trials, such as the WASH Benefits Kenya trial, have previously shown that while nutrition improved linear growth, neither WASH nor nutrition interventions significantly reduced caregiver-reported diarrhea. A critical gap exists in understanding whether these interventions reduced the underlying transmission of specific enteric pathogens, as stool-based analyses capture only point-in-time infections and may miss transient exposures. This study addresses that gap by utilizing serological data to measure cumulative exposure to enteric pathogens during the first two years of life.

Methodology
This analysis utilized banked dried blood spot (DBS) specimens from the WASH Benefits Kenya cluster-randomized trial. The study focused on a 2x2 factorial subset of the trial arms: a control group, a WASH intervention group (improved water, sanitation, and handwashing), a nutrition intervention group (counseling and lipid-based nutrient supplements), and a combined WASH plus nutrition group.

• Study Population: The primary analysis included 3,030 children from 384 clusters in rural western Kenya, with a median age of 23 months at the final visit. Specimens were collected at target ages of 6, 12, and 24 months.
• Laboratory Assay: A multiplex bead assay was used to measure pathogen-specific Immunoglobulin G (IgG) responses in DBS samples. The panel included antigens for 12 enteric pathogens: Norovirus (GI and II), Campylobacter spp., Heat-labile toxin-producing Enterotoxigenic E. coli (LT-ETEC), Shigella/Enteroinvasive E. coli (EIEC), Salmonella enterica (LPS groups B/D and HlyE for Typhi/Paratyphi), Vibrio cholerae, Cryptosporidium, Giardia duodenalis, Entamoeba histolytica, Taenia solium, and Strongyloides stercoralis.
• Statistical Analysis: The primary outcome was IgG seroprevalence at the final visit (approx. 24 months). Analyses followed an intention-to-treat approach, estimating risk differences between WASH vs. no-WASH and nutrition vs. no-nutrition using linear-binomial regression with cluster-robust standard errors. P-values were adjusted for multiple comparisons across the 12 pathogens using the Benjamini–Hochberg procedure (5% false discovery rate). Secondary analyses examined seroprevalence at 12 months and age-seroprevalence curves.

Key Results

• High Transmission Burden: Enteric pathogen seroprevalence increased rapidly with age. By the final visit, seroprevalence exceeded 90% for Campylobacter, LT-ETEC, and Norovirus. High prevalence was also observed for Shigella/EIEC (>80%) and Cryptosporidium (80%).
• Intervention Effects: At the final visit (24 months), differences in seroprevalence between intervention and control groups were small and generally not statistically significant after correction for multiple comparisons.
  • WASH vs. Control: WASH was associated with lower T. solium seroprevalence (−3.3 percentage points) and higher E. histolytica seroprevalence (+3.2 percentage points), but neither met the false discovery rate threshold.
  • Nutrition vs. No Nutrition: Nutrition was associated with lower V. cholerae (−1.1 percentage points) and Shigella/EIEC (−2.7 percentage points) seroprevalence, but these also failed to meet the significance threshold after adjustment.
• Secondary Findings: Analyses at the 12-month visit (period of highest adherence) showed modest evidence of reduced Giardia and E. histolytica seroprevalence in WASH groups and reduced LT-ETEC in nutrition groups. However, these effects were not sustained at the final visit.
• Age-Seroprevalence Curves: Curves suggested modest delays in seroconversion for some pathogens in intervention groups (e.g., Giardia, S. enterica Typhi/Paratyphi with WASH; Shigella/EIEC, LT-ETEC with nutrition), but the curves largely converged by age two, indicating transient rather than sustained reductions in exposure.
• Norovirus Anomaly: Contrary to expectations, Norovirus seroprevalence was higher in intervention arms than in the control group around 12 months.

Significance and Claims
The authors conclude that at the adherence levels achieved in this setting, household-level WASH and nutrition interventions were insufficient to reduce widespread early-life enteric pathogen exposure. The lack of clear effect on seroprevalence at the final visit aligns with the trial's primary findings regarding diarrhea and growth.

The paper posits that the limited effects likely reflect continued exposure through pathways not adequately addressed by household interventions, such as animal feces, contaminated food, and environmental contamination outside the compound. The study highlights that serology provides a cumulative measure of exposure that stool testing may miss, revealing that despite high intervention adherence in the first year, transmission remained intense.

The authors suggest these findings support the need for complementary strategies, such as vaccines and broader transmission-control measures, rather than relying solely on household WASH and nutrition. Additionally, the study establishes a pre-vaccine serological benchmark for typhoidal Salmonella (HlyE) in rural Kenya, noting that nearly one-quarter of children were seropositive by age two, indicating substantial exposure prior to the introduction of typhoid conjugate vaccines. The paper emphasizes that while interventions may cause transient delays in exposure, they did not achieve sustained reductions in cumulative exposure in this high-transmission environment.