Integrating a Geographic Information System to Explore the Effect of Water, Sanitation,and Hygiene on Trachoma at Aggregate Spatial Scales Öffentlichkeit
Altherr, Forest (2017)
Abstract
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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