Spatial Analysis of Cholera in Kaduna State, Nigeria
The focus of this research is to analyze the spatial patterns and clusters of cholera epidemic in five local government areas (LGAs) of Kaduna State with the aid of Geospatial techniques. To analyze the spatial pattern and clusters of cholera epidemic in the study area, inventories provided by the Ministry of Health Kaduna State, coordinate of the locations of towns and localities were used for the analysis in ArcGIS 10.3 software environment and R Statistical software. The method employed in this study is Ripley’s k-function method to determine spatial clusters of Cholera epidemic, analyze spatial pattern of cholera, identify disease clusters and risks using Geospatial Technology (GIS). The result shows that there are about I87 locations of patients with Cholera disease cases in the study area from the year 2010 to 2015. Amongst the study area, Zaria Local Government Area, has the highest number of about 71 locations which constitutes about 37.97%, Igabi Local Government with 53 locations constituting about 28.34%, Sabon Gari Local Government with 19 locations constituting about 10.16%, Kaduna South Local Government having 28 locations constituting 14.97%, and Kaduna North with the lowest locations of about 16 patients (8.56%). It was found that there were about 1,363 reported cases of people with Cholera disease in Igabi LGA, being the area with the highest number and with 217 cases in Zaria which is the lowest. The result showed that four among the five local governments were clustered with the exception of Kaduna North for which the disease pattern is random. Moreover, the result revealed that the overall spatial pattern of cholera epidemic in the study area is clustered, and the overall cholera disease risk was more concentrated in Igabi and Kaduna South LGA.
1.1 Background to the Study
Spatial statistics is the process of extracting or creating new information about a set of geographic features to perform routine examination, assessment, evaluation, analysis or modeling of data in a geographic area based on pre-established and computerized criteria and standards. It is a technique for analyzing spatial data mostly on human scale. Complex issues arise in spatial analysis, many of which are neither clearly defined nor completely resolved. The most fundamental of these are the problems of defining the spatial location of the entities being studied (Scott and Getis, 2008).
Nigeria is a prime area in studying spatial patterns associated with diseases because it is a country where millions of people live in close proximity not only to other people but also to open and unsafe water sources and refuse dumps. It is also a country that is actively engaged in alteration of its aquatic ecosystems, a process often associated with changed disease ecologies (WHO 1993). Cholera is one of the deadliest diseases in Africa (WHO 1993), within 2-3 hours of unset symptoms, a previously healthy person may severely become dehydrated and if not treated may die within 24hours (Sack et al 2004; WHO 2010). A link between cholera, phytoplankton blooms and copepod zooplankton has been demonstrated in Asia (Colwell et al., 1996). The African Great Lakes have been suspected to play a role as reservoirs of the bacteria Vibrio cholerae (v.cholerea), while human infection and movement are probably involved in the propagation of the disease inland. During the 19th century, cholera spread repeatedly from its original reservoir or source in the Ganges delta in India to the rest of the world, before receding to South Asia (WHO 2008).
Six pandemics were recorded that killed millions of people across Europe, Africa and the Americas. The seventh pandemic, which is still on going, started in 1961 in South Asia, reached Africa in 1971 and the Americas in 1991. The disease is now considered to be endemic in many countries and the pathogen causing cholera cannot currently be eliminated from the environment, WHO (2008). Regions of the world where cholera is currently prevalent are Africa, Asia and parts of the Middle East. Imported cases occasionally occur in richer countries in travelers returning from endemic areas, (National Travel Health Network and Centre (2007). The disease no longer poses a threat to countries with minimum standards of hygiene, but it remains a challenge to countries where access to safe drinking water and adequate sanitation cannot be guaranteed, (WHO, 2009). The mechanistic basis for a climate-cholera connection involves multiple pathways and the primary transmission from environmental reservoirs initiates seasonal outbreaks of cholera in endemic regions, (Pascual et al, 2002).
GIS and epidemiological approaches are helpful tools to control the disease spatially and temporally. GIS is a computer system for capturing, storing, querying, analyzing, and displaying geospatial data (Chang, 2008). The general functions of GIS in health studies are disease mapping and modeling, spatial and spatial-temporal changes analysis and risk assessment, public health care and hospital management. GIS is an integrated collection of computer software and data used to view and manage information connected with specific locations, analyze spatial relationship and model spatial processes. GIS has the capabilities of analyzing the spatial patterns and distribution of disease and its influential environments towards creating an innovative cholera control plan in the country. Spatial epidemiology is an essential approach in understanding of spatial disease risk transmission and pattern particularly disease mapping and descriptive analysis (Chin-Lai, 2009). This study explores spatial analysis toolset in R statistical package, ArcGIS and Excel software for cholera mapping and pattern analysis in Kaduna State.
1.2 Statement of the Problem
The threat of cholera rampaging through Nigeria has been a major concern in the country. Recent global health reports show a continual vulnerability of large populations to infectious diseases in relation to our environments. Infectious disease are complex to control and prevent, leading to questions on how to combat them through novel and creative solutions. Cholera is an epidemic and infectious disease which is of global and public health significance.
Thus, it remains a global threat especially in countries where access to clean safe drinking water and sufficient sanitation cannot be assured. The disease has been a public health burden in Nigeria. Although, health scientist and researchers have embraced the use of spatial data in determining the risk of diseases, little has been done to increase the uptake of spatial techniques in health sciences (Grahamm et al; 2004). These research focuses on the use of spatial statistical method to identify the disease pattern and disease risk and Geo-statistical method to map out the disease.
1.3 Significance of the Study
Cholera has been a great concern generally and has impacted negatively on the economies of developing nations. Health workers generally are unable to identify high or risk areas in the areas they operate so as to tailor interventions and do effective health monitoring. Research conducted so far by medical and climate professionals have either lacked knowledge or showed variations on the climate conditions that accompanied the transmission of cholera. The geographical distribution of any major disease forms an important basis for locating appropriate interventions for its control and a means to monitoring their effectiveness. It also provides a possibility for identifying ecological factors with which the disease may be associated.
The link between climate and medical data has not been well defined, and health information system have been weak due to the lack of case detection, irregularity in reporting and poor coordination (WHO, 2009).There is the need to draw more attention to hot spots and areas where intervention measures can be tailored to improve monitoring of the occurrence, distribution and control of cholera in different geographical areas and time periods. This can be used by health workers or officials to make appropriate planning and resource allocation in limiting the outbreak. Spatial statistical method is also necessary to analyze the pattern that are associated with the spatial distribution of cholera at different geographical locations in the study area.
1.4 Aim and Objectives
The aim of this study is to determine the spatial heterogeneity of cholera epidemic in Kaduna state. The specific objectives through which the stated aim will be achieved are to:
(i) Generate eminent spatial patterns in the data set through spatial map.
(ii) Evaluate the degree of spatial clusters of disease locations and disease risks.
(iii) Create an inventive cholera control plan.
1.5 Definition of Terms
1. Spatial Analysis: Technique for analyzing spatial data or human scale mostly geographic data or techniques applied to structures at human scale, most notably in an analysis of geographic data.
2. Epidemic: Rapid spread of infectious disease to a large number of people in a given population within a short period of time, or an outbreak or unusually high occurrence of disease or illness in a populated area.
3. Epidemiology: The study of the patterns, causes and effects of health and disease condition in a defined population.
4. Cholera: Is an acute diarrhea infection caused by ingestion of food or water contaminated with the bacterium vibrio cholera.
5. Disease: Can be seen as a disorder from the normal healthy state of the body, soul and mind of human being, which manifest is itself in an abnormal development of the physical, physiological and mental state of the human being concerned.
6. Threat: An expression of an intention to inflict pain, injury, evil or punishment. An indication of impending danger or harm.
7. Contamination: Is the term describing the state of a person or material on coming in contact with disease pathogen.
8. Transmission: The act or process of transferring a disease from one person to another‟
9. Outbreak: A sudden, violent or spontaneous occurrence especially of disease or strife.
10. Infection: The invasion of body tissues by disease causing microorganism, their multiplication and the reaction of body tissues to these microorganisms and the toxins that they produce.
11. Spatial Dependency: Is a key concept on understanding and analyzing spatial phenomena. Such notion stems from what Waldo Tobler calls the first law of geography: “everything is related to everything else, but near things are more related than distant things.”
12. Risk Factor: Any attribute, characteristic or exposure of an individual that increases the likelihood of developing a disease or injury.