Towards sustainable TB control in Ethiopia – profiling high-risk geographical areas using spatial modelling

Abstract

Tuberculosis (TB) is responsible for a substantial public health burden worldwide, with a heterogeneous geographical distribution. Sub-Saharan Africa accounts for almost one-quarter of the global burden of TB. This is associated with high HIV-prevalence, low socio-demographic development, and poor living and working conditions. Identification of high-risk populations and locations within countries with a high burden of TB has the potential to improve the cost-effectiveness of TB control strategies.Two groups of 30 countries account for almost 90 per cent of the global burden of TB disease and TB and HIV co-infection. Ethiopia is in both groups, with both high-TB and TB and HIV co-infection. However, information is limited to the geographical distribution of high-risk areas which could inform targeted intervention. The overall aim of the researches in this Thesis is to enhance the TB control program in Ethiopia by providing more detailed knowledge of the distribution of TB, and the contributory role of HIV, low sociodemographic development and poor living and working conditions. This will provide sustained TB control in Ethiopia and enable enhanced strategic implementation of the “End TB strategy.”The first part (Chapters 1-3) of this Thesis highlights the available evidence on the geographical variation of TB and the burden of TB and HIV co-infection. Chapter 4 presents a systematic review of published studies on the effects of altitude and temperature on TB notification. This review indicated that studies examining the correlations between altitude and temperature on TB notification are limited in number. Despite low study power, the report demonstrated that living in low-altitude and high-temperature settings may increase TB risk.Chapter 5 presents evidence from a systematic review and meta-analysis conducted to estimate the prevalence of HIV in patients diagnosed with TB in sub-Saharan Africa. The prevalence of HIV in diagnosed TB patients (HIV/TB) showed substantial heterogeneity with an overall prevalence estimate of HIV/TB of 31.8 per cent. Heterogeneity in HIV/TB between studies was mainly attributable to geographic region and HIV prevalence. The Eastern and Southern sub-Saharan African region had a higher prevalence of HIV/TB (34.4 per cent) compared to Western and Central sub-Saharan Africa (27.3 per cent). However, the prevalence decreased more in the Eastern and Southern sub-Saharan African region than Western and Central sub-Saharan African between 2000 and 2010. This study suggests that collaborative TB and HIV activities need to be strengthened and sustained to achieve an end to the TB epidemic.Based on evidence from previous chapters, Chapters 6 and 7 present the spatial distributions of TB and HIV, profiling the sociodemographic and environmental determinants in the Amhara region of Ethiopia, using separate TB and HIV cluster detection methods. These studies demonstrated the spatial heterogeneity of both diseases. Both district-level TB notifications, reported between 2014 and 2017, and HIV infection rates, between 2015 and 2017, were spatially clustered in the border areas of the Amhara region of Ethiopia. Regression analyses demonstrated that the most important factor associated with both TB and HIV clustering was the proportion of seasonal migrant populations in the district. Additional factors associated with high notifications of TB were the proportion of people living in urban areas, crowding, the percentage of males, people living with HIV (PLHIV) /1000 population, access to health care, and the use of charcoal for cooking. Living at low altitude was also associated with TB clustering, which was consistent with the review findings in Chapter 4. Low educational status was also associated with HIV high-risk areas.Chapter 8 presents the epidemiology of TB and HIV co-infection in Ethiopia. This chapter elucidates the progress of the implementation of collaborative TB and HIV activities and the consequent impact on the national TB control program. Findings from sentinel surveillance of TB and HIV co-infection data, from 76 health facilities in Ethiopia, suggest that collaborative TB and HIV services were either not uniform or not consistently implemented between 2010 and 2015. However, encouragingly, intensified TB case finding in PLHIV and the screening of HIV patients for TB diagnosis increased. This Thesis provides more detailed evidence on the distribution of TB and associated HIV infection in Ethiopia, using geo-spatial tools and modelling. It shows that TB and HIV infection are geographically heterogeneous and co-clustered in the Northwest border areas of Ethiopia, likely influenced by the proportion of seasonal migrants in common. This information provides the basis to enhance the strategic implementation of TB control program in Ethiopia. It also highlights the need to strengthen integrated TB and HIV management, to address social determinants of TB, and to deal with issues of population movement to control and prevent HIV and TB in Ethiopia, and thus achieve the “End-TB” goal.