HIV Transmission in the Era of Scaling up Antiretroviral Therapy in Ethiopia

The goal of this observational study is to understand patterns of HIV transmission in a high-prevalence area in Ethiopia, and to compare viral genetic information in people with HIV who are newly diagnosed and have not been exposed to antiretroviral therapy with persons receiving antiretroviral therapy without viral suppression. The main questions it aims to answer are: * Do people with HIV who fail to achieve viral suppression contribute to the ongoing spread of HIV in Ethiopia, or does HIV transmission mainly occur between persons with no exposure to such therapy? * Are viruses with drug-resistance mutations transmitted onwards from people with HIV receiving antiretroviral therapy who fail to achieve viral suppression? \* Which factors are involved in treatment failure and emergence of drug-resistant viruses longitudinally? Participants will be enrolled with regard to history of antiretroviral therapy exposure (newly diagnosed/treatment-naïve vs. treatment-experienced with lack of viral suppression), using persons on antiretroviral therapy with viral suppression for control. We will compare the following outcomes between these groups: * Clustering of viral genetic sequences at inclusion (implying linked transmission) * Prevalence of drug-resistance-associated mutations at inclusion * Viral suppression and emergence of drug-resistance mutations during follow-up