Triple-class antiretroviral resistance will be defined according to IAS-USA interpretive guidelines: NRTI class - 3 thymidine or non-thymidine-associated mutations (excluding the M184V mutation) or a multi-nucleoside resistance mutation in reverse transcriptase; PI class - 3 protease mutations, including 1 primary mutation; NNRTI class - 1 primary (K103N or Y188L) or 2 secondary NNRTI-associated mutations in reverse transcriptase.