Geographical Patterns and Environmental Risks of Inflammatory Bowel Disease and Diarrhoea A Comparative Study Using Spatial and Statistical Modelling

The aim of this PhD study is to investigate multiple aspects of environmental and epidemiological factors influencing inflammatory bowel disease (IBD) in the UK and diarrhoeal disease in children under five in two informal settlements of Accra, Ghana: Gbegbeyise (GB) and Madina Zongo (MZ). While IBD is a chronic non-communicable condition with rising incidence in industrialised countries, diarrhoeal diseases remain an acute public health threat in low-income urban environments. This thesis comprises four studies that apply spatial analysis and regression-based modelling to examine these distinct disease contexts. The first study investigated IBD in the UK using a novel dataset of 5,452 survey respondents. Grid-based mapping and age-sex standardised morbidity rates (ASMRs) were employed to identify spatial patterns. Findings indicated relatively uniform spatial distributions of Crohn’s disease (CD) and ulcerative colitis (UC) cases but a notable cluster of high CD:UC ratios in North-West England. The second study builds on this by Poisson modelling the relationship between CD risk and the proportion of pasture land, used as a proxy for exposure to Mycobacterium avium subspecies paratuberculosis(MAP). A Poisson regression model at the hydrological catchment level indicated a significant association between CD incidence and pasture proportion, but not for UC, supporting the hypothesis that MAP exposure may contribute to CD risk. The third and fourth studies were conducted in two informal settlements in Accra, Ghana, and focused on childhood diarrhoea. The third study analysed household survey data collected biweekly over a period of more than two years and identified a statistically significant association between diarrhoea incidence and antecedent rainfall and proximity to flood-prone areas. The fourth study evaluated the effect of a WASH intervention in one of the settlements, where a 39.8% reduction in diarrhoea cases was observed. This PhD thesis presents novel findings that enhance the understanding of the spatial distribution of diseases such as IBD and diarrhoea and their relationship with environmental risk factors, providing evidence to the existing literature.