Quantification of Escherichia coli Exposure from Drinking Water and Produce in Low-Income Urban Neighborhoods in Accra, Ghana: Implications for Children's Health 公开

Sizemore, Melissa Anne (2015)

Permanent URL: https://etd.library.emory.edu/concern/etds/0v838072k?locale=zh
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Abstract

Urban environments with overcrowded living situations, inadequate access to sanitation, and dysfunctional water and drainage systems have complex, inter-related webs of fecal-oral transmission routes. Poor, urban residents bear the brunt of these exposures, which manifest as higher incidence rates of diarrhea, especially among children. To compare the risks from different fecal-oral transmission routes, a Quantitative Microbial Risk Assessment (QMRA) was applied to evaluate the risks of exposure to fecal contamination for three drinking water scenarios (consumption of sachet, stored household, or municipal tap water) across three child age groups (0-1, 1-2, and 2-5 year olds), and two food scenarios (children 2-5 or 5-12 years old consuming a street food side salad) in Accra, Ghana. The exposure assessment was based on the concentration of the fecal indicator organism Escherichia coli (E. coli) detected in the three drinking water sources and four produce items that comprise a typical street food side salad (lettuce, cabbage, tomato, and spring onion). Dose estimates from the QMRA were then used to compare the drinking water and food exposure scenarios and identify which represented the greatest microbial risk to children (aged 2-5 years). Consumption of stored household water resulted in the largest average weekly dose estimate (3.61 log10 Colony Forming Units (CFU) E. coli), while consumption of sachet water resulted in the lowest average weekly dose estimate (1.62 log10 CFU). Consumption of a street food side salad produced the second largest average weekly dose estimate (3.28 log10 CFU). Although consumption of a street food side salad did not produce the highest dose estimates, 100 percent of produce items collected from four study communities had quantifiable E. coli concentrations, indicating the potential for exposure to fecal contamination from consuming raw produce items. Educating residents on safe water storage practices and the importance of disinfecting drinking water and produce prior to consumption will lower these exposures; however, improving the intermittent municipal water supply, which drives water storage practices, and developing safer, alternative sources of irrigation water will best mitigate the health risks associated with these exposures.

Table of Contents

TABLE OF CONTENTS

I. BACKGROUND...................................................................... 1

A. Global Childhood Diarrheal Disease Burden................................... 1

B. Fecal-Oral Exposure Pathways................................................. 2

i. Fecal-oral Exposure Pathways: Food.................................... 3

ii. Fecal-oral Exposure Pathways: Fluids................................... 5

C. Identifying Fecal Contamination: The Role of Fecal Indicator Organisms....... 6

D. Health Challenges in Urban Environments..................................... 7

E. The Urban Environment: Accra, Ghana........................................ 9

i. Sanitation in Accra........................................................9

ii. Food Production and Dietary Habits in Accra........................... 10

iii. Drinking Water Sources in Accra........................................ 14

F. Quantitative Microbial Risk Assessment......................................... 15

G. Study Objectives................................................................ 17

II. MANUSCRIPT........................................................................ 18

A. Introduction................................................................... 18

B. Methods....................................................................... 22

i. Study Site................................................................ 23

ii. Data Collection.......................................................... 24

iii. Data Management....................................................... 26

iv. Laboratory Methods..................................................... 27

v. Statistical Methods....................................................... 27

vi. Exposure Assessment.................................................... 28

C. Results.............................................................................. 31

i. Neighborhood Demographics, Drinking Water Sources, and Dietary Habits 31

ii. Microbial Concentrations for Environmental Samples...................... 32

iii. Exposure Assessment..................................................... 34

D. Discussion........................................................................ 36

i. Exposure Dose Estimates.................................................. 36

ii. Microbial Data and Behavioral Characteristics of the Study Populations: Implications for Microbial Risk Assessment 38

E. Conclusions....................................................................... 42

F. References.......................................................................... 44

G. Tables.............................................................................. 48

TABLES

Table 2.1. Population and physical characteristics of study neighborhoods .................................... 48

Table 2.2. Model parameters used to estimate food exposure dose distributions ............................ 49

Table 2.3. Model parameters used to estimate drinking water exposure dose distributions ............ 50

Table 3.1. Reported demographics by neighborhood, Accra, Ghana, 2012........................................ 51

Table 3.2. Reported primary drinking water sources by neighborhood, Accra, Ghana, 2012 ........... 52

Table 3.3. Reported dietary habits by neighborhood, Accra, Ghana, 2012.......................................... 53

Table 3.4. Estimated E. coli concentrations for environmental samples from four stud-neighborhoods in Accra, Ghana, 2011-2012 54

Table 3.5. Monte Carlo simulated E. coli dose estimates for three drinking water scenarios............... 55

Table 3.6. Monte Carlo simulated E. coli weekly dose estimates for two food scenarios.................... 56

Table 3.7. Monte Carlo simulated E. coli weekly dose estimates for all scenarios................................ 57

FIGURES

Figure 2.1. Study site areas: four low-resource urban neighborhoods in Accra, Ghana........................ 58

Figure 3.1. Household survey locations.................................................................................................... 59

Figure 3.2. Distributions of log-transformed E. coli concentration in drinking water samples........... 60

Figure 3.3. Distributions of log-transformed E. coli concentration on produce items........................ 61

Figure 3.4. Distribution of the reported daily volume of water consumed by age group...................... 62

Figure 3.5. Distributions of log-transformed E. coli dose for drinking water scenario A (sachet water) and scenario B (stored household water) 63

Figure 3.6. Distributions of log-transformed E. coli dose for drinking water scenario C (municipal piped water) by neighborhood 64

Figure 3.7. Distribution of log-transformed E. coli dose for food scenarios.......................................... 65

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