Model Input parameters.

In low- and middle-income countries (LMICs), enteric infections and diarrheal diseases among children are widespread due to insufficient water, sanitation, and hygiene (WASH) infrastructure. Children may be exposed to enteric pathogens by ingesting soil contaminated with feces. Although previous research has detected elevated levels of fecal indicator bacteria and enteric pathogen genes in soils, no studies have yet used quantitative microbial risk assessment (QMRA) to assess the potential effect of rainfall on child enteric infections and the potential disease burden via this pathway. We collected a total of 144 soil samples between May and December 2024 in Kibera, Kenya, both before and within an hour after rainfall events from household entrances, compounds, and toilet entrances. Over 70% of soil samples were E. coli positive, with mean concentrations ranging from 51.5 MPN/g of dry soil (SD: 46.1) pre-rainfall to 39.3 MPN/g of dry soil (SD: 45.7) post-rainfall. The reduction was marginally significant (p = 0.058, Kruskal-Wallis test). A one-way ANOVA revealed no statistically significant difference in E. coli levels across sampling locations (p = 0.943) and across latrine types (urine diverting, hanging, pit latrine, and septic tank) (p = 0.46). Using QMRA with soil ingestion parameters specific to children under five years in LMIC settings and locally derived indicator-pathogen ratios for soils, we estimated annual infections and diarrheal disease burden in disability-adjusted life years (DALYs) per person per year. We estimated an annual infection risk of 100% for adenovirus, irrespective of rainfall events. Following rainfall, median annual infection risks attributable to soil ingestion were an estimated 1 in 2 for Campylobacter jejuni, 1 in 31 for Shigella spp., and 1 in 33 for Vibrio cholerae. These findings highlight the potential importance of soil ingestion as an exposure pathway, and point to the need for sanitation improvements to limit the migration of enteric pathogens to soils near living environments.