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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