Quantitative Microbial Risk Assessment of Pediatric Infections Attributable to Ingestion of Fecally Contaminated Domestic Soils in Low-Income Urban Maputo, Mozambique

Rigorous studies of water, sanitation, and hygiene interventions in low- and middle-income countries (LMICs) suggest that children are exposed to enteric pathogens via multiple interacting pathways, including soil ingestion. In 30 compounds (household clusters) in low-income urban Maputo, Mozambique, we cultured Escherichia coli and quantified gene targets from soils (E. coli: ybbW, Shigella/enteroinvasive E. coli (EIEC): ipaH, Giardia duodenalis: beta-giardin) using droplet digital PCR at three compound locations (latrine entrance, solid waste area, dishwashing area). We found that 88% of samples were positive for culturable E. coli (mean = 3.2 log(10) CFUs per gram of dry soil), 100% for molecular E. coli (mean = 5.9 log(10) gene copies per gram of dry soil), 44% for ipaH (mean = 2.5 log(10)), and 41% for beta-giardin (mean = 2.1 log(10)). Performing stochastic quantitative microbial risk assessment using soil ingestion parameters from an LMIC setting for children 1223 months old, we estimated that the median annual infection risk by G. duodenalis was 7100-fold (71% annual infection risk) and by Shigella/EIEC was 4000-fold (40% annual infection risk) greater than the EPA's standard for drinking water. Compounds in Maputo, and similar settings, require contact and source control strategies to reduce the ingestion of contaminated soil and achieve acceptable levels of risk.

Automated summary

Rigorous studies in low-income urban areas of Maputo, Mozambique, suggest that children are at high risk of exposure to enteric pathogens via soil ingestion. Strategies for contact and source control are needed to reduce ingestion of contaminated soil and achieve acceptable levels of risk in similar settings.