Margherita Galli


Ph.D Cycle
XXXIV
Supervisor
Stefano Merler
 
Research Project Title
Modelling the spatial heterogeneity of infectious diseases in sub-Saharan Africa
Research Project Description
Background
In Ethiopia, every year millions of people are infected by infectious diseases. Evidence emerged by epidemiological studies of different kind and related to various diseases have shown that a greater distance from health facilities is associated with lower hospitalization rates [1-3] and higher mortality [1,2,4,5]. However, the burden of infectious diseases is still often estimated on the basis of observed hospitalized cases, which represent an incomplete and biased sample of what is really occuring in the community [6].The role of distance as a barrier to health care access and its influence on individuals’ mortality has been already documented [1-3]. For instance, a cross sectional survey recently conducted in Ethiopia has shown that children who live more than 30km from the health center has a two to three fold greater risk of death than children who live near to an health facility [2]. A recent study focusing on repeated measles epidemics occurred between 2013 and 2017 in this country has highlighted a high heterogeneity in the access to health care and that this phenomenon may dramatically affect the estimation of the burden of measles disease in low-income settings [1]. During these epidemics, the overall number of measles infections in the community might have been more than 8 times higher than the ones recorded at the hospital and the case fatality rate may remarkably increase with travel distance from the well-resourced health facilities: ranging from 0.6% to more than 19% at 20 km from the nearest hospital.

Research project

The research project focuses on the investigation of the complex interplay between the heterogeneous access to primary health care and the mortality rate associated with infectious diseases and on the study of spatio-temporal patterns of epidemic spread in low-income settings. The main challenges of the project will be:
• The development of suitable mathematical models to study spatio-temporal spread of epidemics in sub-Saharan Africa, taking into account the influence of the distance in the hospitalization rate and access to the health care system.
• The estimation of key epidemiological features associated with epidemics observed in low-income settings, such as the transmission potential, incidence and mortality rates in the general community.
The project will focus mainly on measles in Ethiopia, but the developed methods may be also applied to other regions and different diseases, as TB and malaria.

References
[1] Poletti P, Parlamento S, Fayyisaa T, Feyyiss R, Lusiani M, Tsegaye A, et at. The hidden burden of measles in Ethiopia: how distance to hospital shapes the disease mortality rate. BMC Medicine 2018;16:177.
[2] Okwaraji YB, Cousens S, Berhane Y, Mulholland K, Edmond K. Effect of geographical access to health facilities on child mortality in rural Ethiopia: a community based cross sectional study. PLOSONE. 2012;7:3.
[3] Etyang AO, Munge K, Bunyasi EW, Matata L, Ndila C, Kapesa S et al. Burden of disease in adults admitted to hospital in a rural region of coastal Kenya: an analysis of data from linked clinical and demographic surveillance systems. Lancet Glob Health. 2014;2:4.
[4] Rutherford ME, Mulholland K, Hill PC. How access to health care relates to under‐five mortality in sub-Saharan Africa: systematic review. Trop Med Int Health. 2010;15:5.
[5] Dare AJ, Ng-Kamstra JS, Patra J, Fu SH, Rodriguez PS, Hsiao M et al. Deaths from acute abdominal conditions and geographical access to surgical care in India: a nationally representative spatial analysis. Lancet Glob Health. 2015;3:10.
[6] Wolfson LJ, Grais RF, Luquero FJ, Birmingham ME, Strebel PM. Estimates of measles case fatality ratios: a comprehensive review of community-based studies. Int J Epidemiol. 2009;38:1.