Integrating a Geographic Information System to Explore the Effect of Water, Sanitation,and Hygiene on Trachoma at Aggregate Spatial Scales Open Access

Altherr, Forest (2017)

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Trachoma is an infectious disease responsible for a large proportion of the global burden of preventable blindness. The WHO endorsed SAFE strategy (Surgery, Antibiotics, Facial cleanliness, and Environmental improvement) has been implemented at scale throughout Amhara National Regional State of Ethiopia since 2007. The effect of facial cleanliness and environmental improvements on the prevalence of trachoma tends to be contextually dependent, exhibiting variability in prior studies. The aim of this research was to elucidate the relationships between water, sanitation, and hygiene (WASH) indicators and the spatial distribution of trachoma throughout Amhara. Through multi-stage cluster random impact surveys conducted in all districts from 2011 to 2016, trachoma clinical outcomes were collected using the WHO simplified grading scale, and WASH indicators were collected through household and individual level assessments. In the analysis, spatial methods corrected biases that arise from geographic relationships. Disease hotspots, defined as evaluation units with high trachomatous inflammation-follicular among children aged 1 to 9 (TF) in relation to its neighborhood, were identified using TF prevalence estimates and the Getis-Ord Gi* statistic. Socio-demographic, community, and environmental factors thought to promote the clustering of the disease were modeled with logistic regression. The district-level TF prevalence in Amhara ranged from 1.2% to 73.9%. Twelve districts and 325 villages were identified as statistically significant hotspots with 90% confidence. Percentage of children with clean face as well as household access to a water source in less than 30 minutes were significantly associated with a reduced odds of residence in a hotspot. The aforementioned variables as well as household access to a latrine were significant predictors in a spatial lag model of the prevalence of TF. This study demonstrated that water and hygiene are important factors in the clustering of trachoma within a hyperendemic area. Intensified promotion of structural and behavioral interventions to increase WASH coverage may be necessary to eliminate trachoma as a public health problem in Amhara.

Table of Contents

Table of Contents

List of Tables xi

List of Figures xii

Literature Review 1

Introduction 1

Biology and Transmission of Trachoma 2

Evaluation Methods 3

Interventions 5

The Role of Flies in the Transmission of Trachoma 7

Climate and the Fly 9

The Effect of WASH on Trachoma Prevalence 10

Spatial Analysis in Trachoma 12

Literature review methodology 15

Results 17

Discussion 20

Conclusion 23

Introduction 25

Methods 28

Dataset 28

Survey Timing 28

Sample Size 29

Sample selection 30

Selection of clusters 31

Selection of households 31

Trachoma grading 31

Training of Examiners 32

Training of Recorders 32

Household Questionnaire 33

Sociodemographic variables 34

Household Census 35

Descriptive Mapping 35

Mapping Climate and Physical Environment Variables 37

Linear Regression Model Selection 37

Spatial Regression 38

Hot Spot Identification 40

Hot Spot Regression Analysis 41

Results 43

Study area and population 43

Overall prevalence and geographic distribution 43

Risk factors and their geographic distribution 44

Linear Regression Analysis 45

Gott Hotspot Analysis 48

Gott Hotspot Logistic Regression 49

Woreda Hotspot Analysis 54

Woreda Hotspot Logistic Regression 55

Hotspot Model Comparison 57

Discussion 59

Clean Face as a Predictor 59

Household Water Access 62

Household Latrine Access 64

Spatial Analysis 65

GWR Model 67

Spatial Lag Model 68

Woreda Hotspot Logistic Regression Model 69

Gott Hotspot Logistic Regression Model 70

Strengths and Limitations 72

Strengths: 72

Limitations: 74

Public Health Significance and Recommendations 78

References 84

Tables 93

Figures and Figure Legends 98

Appendices 124

Appendix A. Maps showing the study location at increasingly smaller scale 124

Appendix B. Woredas throughout the Amhara Regional State of Ethiopia 124

Appendix C. Geographic range of zones throughout the Amhara National Regional State of Amhara 125

Appendix D. Studies evaluating clustering of trachoma at varied spatial scales 126

Appendix E. Studies using trachoma as an outcome that considered exposure as distance to a point of interest as a risk factor 127

Appendix F. Studies that used trachoma as the primary outcome and considered exposure to geoclimatic variables as risk factors 128

Appendix F. Conceptual diagram explaining the modelled relationship and the influence of hypothesized confounders 129

Appendix G. Conceptual diagram showing how spatial autocorrelation affects the assumption of uncorrelated error terms and intendent observations. The right side of the diagram indicates how adding a lag parameter can control for the diffusion process of geographic neighbors. 130

Appendix H. Survey Tools 131

Appendix I. Institutional Review Board Exemption Letter 138

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