Laboratory tests: A blood sample is used for resistance testing in treatment naive patients. For patients on ART, the initial sample will be used for HIV viral load measurement at the IDI. Part of the sample will be frozen (-80°C) and stored at the IDI for later resistance testing in case of detectable viral load (plasma viral load >1000 copies/ml). Resistance testing will be done at the Ugandan Virus Research Institute (UVRI) in Entebbe, Uganda.