Assessment of Exposure to Fecal Contamination at Beaches in Low-Income Neighborhoods in Accra, Ghana 公开

Santander, Amanda Sue (2014)

Permanent URL: https://etd.library.emory.edu/concern/etds/xw42n8256?locale=zh
Published

Abstract

Background: In developing countries, there are many pathways by which children may be exposed to fecal contamination, especially in urban areas where overcrowding is common and water and sanitation systems are poor. The purpose of this study was to identify and quantify risk of exposure to fecal contamination at beaches and in marine water in low-income neighborhoods in Accra, Ghana.

Methods: This study used household surveys, environmental samples, and structured observations of children at beaches to characterize marine water and sand as exposure pathways to fecal contamination. Two coastal neighborhoods in Accra were selected for the study, and eight exposure scenarios were identified in order to estimate exposure dose of selected indicator microorganisms.

Results: The geometric mean E. coli concentration in marine water samples was 3.98 cfu log10/100ml and the geometric mean concentration in sand samples was 2.53 cfu log10/100g. This concentration did not differ significantly by neighborhood. There was a significant difference in the concentration of E. coli and coliphage in sand versus water samples (p < 0.02). The exposure scenario resulting in the highest dose of fecal contamination was direct contact with sand on the beach, which resulted in a mean E. coli dose of 1339 cfu/event for children under five years and 1749 cfu/event for children 5-12 years. Pair-wise comparisons of exposure dose distributions found no significant different in dose for children under five years compared with children ages 5-12 years. However, comparisons of exposure activity (direct contact with sand, contact with object, head submerged in water, or head not submerged in water) showed significant differences in dose.

Conclusions: Both water and sand at beaches in Accra are highly contaminated due to runoff from fecal sludge discharge sites and from open defecation by beachgoers. Previous studies may have overestimated the risk of exposure to pathogens in the marine water by assuming a greater volume of water ingested during swimming events. The use of stochastic models in this study helped to control some of the variability and uncertainty in the exposure scenarios that were not accounted for previously.

Table of Contents

Table of Contents


I. Background .....................1
A. The Burden of Diarrheal Disease in Developing Countries.....................1

B. Sanitation Challenges in Urban Environments.....................2

C. Sanitation and Fecal Sludge Disposal in Accra, Ghana.....................2

D. Recreational Water, Beaches, and Health.....................4

E. Indicator Organisms of Fecal Contamination.....................6

F. Quantitative Microbial Risk Assessment of Recreational Water Exposures.....................8

G. Study Objectives.....................11

II. Manuscript.....................13

A. Abstract.....................13

B. Introduction.....................14

C. Methods.....................16

i. Site Selection.....................16

ii. Data Collection.....................16

iii. Laboratory Methods.....................18

iv. Data Management.....................18

v. Statistical Methods.....................18

vi. Exposure Assessment.....................19

D. Results.....................23

i. Neighborhood characteristics.....................23

ii. Microbial concentrations at beaches.....................24

iii. Exposure assessment.....................25

E. Discussion.....................26

i. Exposure Model for Recreational Water and Sand.....................26

ii. Limitations of the Exposure Dose Model.....................27

iii. Implications of Structured Observations and Microbial Concentrations for Microbial Risk Assessment.....................28

F. Conclusions.....................30

G. References.....................32

H. Tables.....................36

I. Figures.....................43

III. Implications, and Future Study.....................47

A. Public Health Implications.....................47

B. Future Studies..................... 47

IV. Appendix..................... 49

A. IRB Approval.....................49

B. Household Survey.....................51

C. Large Volume Water Environmental Sample Collection Form.....................59

D. Particulate Environmental Sample Collection Form.....................60

E. Beach Description and Conditions Structured Observations Form.....................61

F. Table 7. Exposure Scenario Results for a Deterministic Model.....................64

G. Tables 8 and 9. Structured observations for children at beaches......................65

List of Tables
1. Hand & Object Contamination Parameters
2. Exposure Dose Parameters
3. Descriptive Statistics from Household Surveys
4. E. coli and coliphage concentrations in sand and marine water samples by neighborhood
5. Exposure Scenario Results
6. Pair-wise comparisons of exposure doses by microbe, activity, and age group


List of Figures
1. Transmission pathways of fecal-oral illnesses
2. Map of study neighborhood
3. Kernel density plot of microbe concentrations in sand
4. Kernel density plot of microbe concentrations in marine water

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