Exploring spatial patterns and hotspots of hepatitis A and amoebic dysentery using GIS and geostatistical analysis in Turkey

Epidemics of Infectious diseases have been documented throughout history and recent global health reports show a continual vulnerability of a large number of people to infectious diseases such as Hepatitis A (HAV) and Amoebic Dysentery (A Dysentery or AD) in relation to their environment. Of particular concern is the epidemic outbreaks patterns of Hepatitis A and A Dysentery incidences in terms of their geographic distributions. Accurate statistics on the geographical distribution of different endemicities of Hepatitis A and A Dysentery, on the populations at risk, and on the implications of given levels of endemicity for morbidity and mortality are important for effective control of these diseases. These estimates can be obtained using Geographical Information Systems (GIS) in conjunction with geostatistical methods available to examine patterns of disease incidence, morbidity and mortality in space and time and to relate those patterns to the identification of potential causes of disease, such as environmental exposure, diet and unhealthy behaviours, economic or socio-demographic factors. In this sense, spatial epidemiology, one of the tools for improving public health, is increasingly being used to assess health risks associated with environmental hazards. In most cases, epidemiological analyses are based on observations of disease occurrence in a population of people 'at risk'. Typically, we want to relate occurrence patterns between collections of people experiencing different levels of exposure to some factor having a putative impact on a person's risk of disease. In recent years, the research in environmental health issues is constantly becoming more and more effective owing to the use of both various information technology services and software. In this context, it's no doubt that the use of GIS and Geostatistical methods helps in identification and quantification of patterns in disease occurrences providing the first steps toward increased understanding and possibly, control of the diseases. The thesis focused on providing an insight into the geographic distribution of Hepatitis A and A Dysentery incidence in terms of their temporal distribution, spatial patterns, hotspots and clusters identification in 81 provinces of Turkey. Hepatitis and Dysentery have been a public health burden in Turkey. These diseases are a significant cause of morbidity, even if the mortality rate is low. The endemicity of this infections varies due to sanitary and hygiene conditions and socio-economic differences among the countries and in various regions of the same country. Turkey is a middle endemic area with respect to Hepatitis A virus and A Dysentery infection. However, because of the geographical, economical, environmental and cultural differences among the provinces of Turkey, the frequency of this infection also varies due to sanitary / hygiene conditions and socio-economic differences in various regions of the country. Within the scope of the study, first, spatial epidemiology was described and reviewed, different approaches in disease modeling were provided. Hepatitis A and A Dysentery transmission and their burdens in Turkey were discussed. The benefits of disease mapping and smoothing techniques in spatial epidemiology were pointed out and the distinction between GIS and geostatistics were outlined. This research project made use of data obtained from the EnviroGRIDS project supported by the European Union within the 7th Framework Programme. In this context, the data for patients with Hepatitis A and A Dysentery at province level for 2001-2011 obtained from Turkish Ministry of Health and the census data for 2000-2011 provided by the State Statistical Institute of Turkey were used as a basis for further analysis. Visual data mining was performed using Boxplots which give general insights of HAV and AD morbidity rate and time series thematic maps which helped us identify space-time disparities. The global Moran's statistic demonstrated that there was clustering in the year 2005, 2006 and 2007 for Hepatitis A in Turkish population as a whole, 2002, 2003, 2006 and 2007 for Hepatitis A in Turkish children below 15 years and in 2006 and 2007 for A Dysentery. After a general statistical analysis of the LISAs techniques which measured HAV and AD infections at the local level it was found that there is a decreasing trend in the morbidity rate of Hepatitis A and A Dysentery at epidemic level from 2001 to 2011. The LISA statistic showed that majority of the HAV and AD clusters and hotspots were relatively located in the Black Sea and Central Anatolia Region for all the years, covering the Kizilirmak, Yesilmak, Sevhan River Basin and Western Black Sea River Basins in Turkey. However, from 2006-2008, hotspots started to return slowly to the western part of Turkey and spreading to the Eastern Anatolia Region. The western provinces with higher HAV and AD morbidity rate could be found in the Marmara, Menderes, Western Black Sea and Gediz River Basins, while on the Eastern Anatolia Region high HAV and AD morbidity rate were observed in the Aras, Firat-Dicle and Van Golu River Basins. From 2009-2011, the hotspots and clusters attenuated significantly in HAV and AD infections. Also, it was noted that children under the age of 15 years were more infected with Hepatitis A. Specifically, age-group-5-9 revealed the highest HAV morbidity rate than the other age groups. Our approach of identifying and quantifying of space-time disparities, clustering, and hot spots provided useful and detailed information for guiding policy formulation to succinctly address the burden of Hepatitis A and A Dysentery and possibly, curtail the spread of these particular diseases in the Turkish population.