CD4 and mitochondrial DNA depletion syndrome 4a: The aim of this study was to describe the proportion of adults living with HIV who have AHD, defined as a CD4 count of less than 200 cells per mm3, identify factors associated with the development of AHD, including socioeconomic, demographic, and health-care related determinants, and estimate the number of individuals with AHD in sub-Saharan Africa.