CD4 and AIDS: There are various factors that increase the chance of TB infection among HIV/AIDS patients including CD4 cell count and the number of viral loads11,12, household family size, cigarette smoking, baseline CD4 cell counts, WHO clinical stages, having a history of diabetics13, and etc. However, these factors have not been studied in the context of survival analysis, where association between risk factors and time to TB co-infection might be of interest.