Quantitative assessment of exposure to fecal contamination in urban environment across nine cities in low-income and lower-middle-income countries and a city in the United States

Abstract

Background: During 2014 to 2019, the SaniPath Exposure Assessment Tool, a standardized set of methods to evaluate risk of exposure to fecal contamination in the urban environment through multiple exposure pathways, was deployed in 45 neighborhoods in ten cities, including Accra and Kumasi, Ghana; Vellore, India; Maputo, Mozambique; Siem Reap, Cambodia; Atlanta, United States; Dhaka, Bangladesh; Lusaka, Zambia; Kampala, Uganda; Dakar, Senegal.

Objective: Assess and compare risk of exposure to fecal contamination via multiple pathways in ten cities.

Methods: In total, 4053 environmental samples, 4586 household surveys, 128 community surveys, and 124 school surveys were collected. E. coli concentrations were measured in environmental samples as an indicator of fecal contamination magnitude. Bayesian methods were used to estimate the distributions of fecal contamination concentration and contact frequency. Exposure to fecal contamination was estimated by the Monte Carlo method. The contamination levels of ten environmental compartments, frequency of contact with those compartments for adults and children, and estimated exposure to fecal contamination through any of the surveyed environmental pathways were compared across cities and neighborhoods.

Results: Distribution of fecal contamination in the environment and human contact behavior varied by city. Universally, food pathways were the most common dominant route of exposure to fecal contamination across cities in low-income and lower-middle-income countries. Risks of fecal exposure via water pathways, such as open drains, flood water, and municipal drinking water, were site-specific and often limited to smaller geographic areas (i.e., neighborhoods) instead of larger areas (i.e., cities).

Conclusions: Knowledge of the relative contribution to fecal exposure from multiple pathways, and the environmental contamination level and frequency of contact for those "dominant pathways" could provide guidance for Water, Sanitation, and Hygiene (WASH) programming and investments and enable local governments and municipalities to improve intervention strategies to reduce the risk of exposure to fecal contamination.

Keywords: Exposure assessment; Fecal; LLMIC; Multi-city; Pathway; WASH.

Graphical abstract

Fig. 1

Conceptual diagram of the SaniPath exposure assessment.

Fig. 2

Environmental fecal contamination across cities for different sample types. The box of boxplot presents 25th percentile (Q1), median, and 75th percentile (Q3). The whiskers represent the Q1–1.5IQR (interquartile range) and Q3 + 1.5IQR. The unit of E. coli concentration for all the water samples is either colony-forming unit (CFU) for membrane filtration or most probable number (MPN) for IDEXX per 100 mL. The E. coli units of concentration are CFU or MPN per serving for produce and street food, CFU or MPN per swab for public latrine swabs, and CFU or MPN per gram of soil. The results are color coded by city. Labels at the bottom indicate boxes with hidden colors. Types of Other Drinking Water samples are labeled on the top of the boxes. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Combined behavior frequency of contacting various environmental pathways across cities from household surveys, community surveys, school surveys. The frequency categories vary by pathway. For open drains, ocean water (Oc.), and surface water, the categories are never, 1 to 5 times per month, 6 to 10 times per month, and more than 10 times per month. For bathing water, flood water, public latrines, raw produce, and street food, the categories are never, 1 to 5 times per week, 6 to 10 times per week, and more than 10 times per week. For municipal drinking water and other drinking water (DW), the categories are never, 1 to 3 days per week, 4 to 6 days per week, and every day.

Fig. 4

Total fecal exposure by pathway across cities. The height of a bar represents the log scale total exposure from all the pathways while different colors represent the contributions from specific pathways. The unit of exposure to E. coli is CFU/MPN per month. The names of neighborhoods that correspond to the neighborhood IDs are shown in Table 4.