Quantification of Exposure to Open Drains in Low-Income Neighborhoods in Accra, Ghana: Implications for Microbial Risk Assessment Pubblico

Abstract

In developing countries, high rates of urbanization are adding pressure to already stressed water and sanitation systems that are critical to the health of urban communities. Inadequate access to improved sanitation, coupled with limited sewage collection and treatment can cause widespread fecal contamination of urban environments. Drainage networks, commonly present in these settings, act as the primary outlet for wastewater. Drains are rarely covered completely, allowing residents, especially children, to be easily exposed to their contents. This study used extensive microbiological sampling, behavioral observation, drain characterization, spatial mapping, and exposure assessment to comprehensively examine open drains as a route of exposure to fecal contamination in four low-income neighborhoods in Accra, Ghana. Drains that were originally rivers or lagoons had a mean E. coli concentration of 6.99 cfu log10/100ml, while drains that were not, had a mean E. coli concentration of 8.44 cfu log10/100ml. All drains had a mean coliphage concentration of 4.61 pfu log10/100ml. After excluding drains that were originally rivers or lagoons, E. coli and coliphage concentrations did not differ significantly by neighborhood, drain size, construction type, or coverage. All children were observed entering small drains at a lower rate than large drains, and children under 5 years old were observed entering formally-constructed drains at a lower rate than ecologically-formed drains. A stochastic model of six exposure scenarios was constructed to estimate ingestion of drain water via mouthing of contaminated hands. Pairwise comparisons of exposure dose distributions by child age (under 5 years or 5-12 years) and exposure activity (accidental entry, deliberate entry, or entry to fetch an object) found no differences in doses. High concentrations of microbial contamination in drains were the primary determinant of exposure dose compared to type of exposure activity and child age. Exposure doses calculated in this study were significantly lower than previous estimates that assumed 5mL of drain water was directly ingested. Differences in the drainage network by neighborhood, and drain entry behavior by drain characteristic, suggest that risk of enteric disease from open drains is likely not uniform throughout the city. Drains should be covered to mitigate this serious public health risk.

Table of Contents

I. BACKGROUND.............................................................................................. 1 A. The Global Burden of Diarrheal Disease.............................................................. 1 B. Sanitation Challenges in Urban Environments...................................................... 2 C. Sanitation in Accra, Ghana: The Role of Open Drains........................................... 4 D. Drainage Systems and Health.......................................................................... 7 E. Quantitative Microbial Risk Assessment of Wastewater Exposures........................... 8 F. Study Objectives.......................................................................................... 13 II. MANUSCRIPT.............................................................................................. 14 A. Introduction................................................................................................. 14 B. Methods...................................................................................................... 16 i. Study Site..................................................................................................... 16 ii. Data Collection.............................................................................................. 18 iii. Data Management......................................................................................... 20 iv. Laboratory Methods...................................................................................... 20 v. Spatial Analysis.............................................................................................. 20 vi. Statistical Methods........................................................................................ 22 vii. Exposure Assessment.................................................................................... 23 C. Results........................................................................................................ 30 i. Neighborhood Demographics and Sanitation Practices............................................ 30 ii. Open Drain Characteristics............................................................................... 32 iii. Observed Behavior of Children Around Open Drains............................................... 35 iv. Microbial Concentrations in Open Drains............................................................. 36 v. Exposure Assessment...................................................................................... 37 D. Discussion..................................................................................................... 39 i. Drain Exposure Model....................................................................................... 39 ii. Microbial Concentrations in and Structured Observations of Open Drains: Implications for Microbial Risk Assessment....................................................................................................... 42 E. Conclusions.................................................................................................... 44 F. References..................................................................................................... 45 G. Tables........................................................................................................... 49 H. Figures.......................................................................................................... 65 III. LESSONS LEARNED AND FUTURE ANALYSES..................................................... 78 A. Lessons Learned.............................................................................................. 78 B. Future Analyses............................................................................................... 81 IV. APPENDIX.................................................................................................... 84 A. Cyclic pattern of exposure to fecal microbes......................................................... 84 B. Household Survey............................................................................................. 85 C. Drain Characterization Tool................................................................................. 93 E. Pictorial Examples of Drain Classifications.............................................................. 94 E. Structured Observation Tool............................................................................... 98 F. Environmental Sample Collection Form................................................................. 100

About this Master's Thesis

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School	Rollins School of Public Health
Department	Epidemiology
Degree	MPH
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health
Parola chiave	Exposure assessment Microbial risk assessment Ghana GIS Open drains Urban health Wastewater Stochastic modeling WASH
Committee Chair / Thesis Advisor	Moe, Christine L, Emory University
Committee Members	Clennon, Julie, Emory University
Partnering Agencies	Emory University schools, faculty or affiliated programs

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