The in-house genotypic drug resistance test will be performed to determine the drug resistance profiles for the HIV-1 pol gene, focusing on protease, reverse transcriptase, and integrase. Drug resistance mutations will be identified with the use of the HIVdb program of the Stanford University HIV Drug Resistance Database (http://hivdb.stanford.edu), in accordance with the drug-resistance mutation list of the International AIDS Society-USA Consensus Guidelines [24]. Strains with genetic mixtures of wild-type and mutant sequences at amino acid residues that code for major drug resistance will be considered to be drug resistant. Based on the interpretation given by the HIVdb program, sequences will be divided into the drug-resistant sequences, interpreted as having high, intermediate, and low levels of resistance, and the sensitive sequences, interpreted as the sensitive and potentially resistant. Multi-drug resistance (MDR) will be defined as having genotypic resistance to more than one class of antiretroviral drugs. Reference sequences of various subtypes and recombinants will be retrieved from the Los Alamos database (http://hiv-web.lanl.gov/seq-db.html). Sequences will be aligned with the Clustal W listed in the MEGA (molecular evolutionary genetics analysis) analytical package (version 3.0) [25] with minor manual adjustments. The phylogenetic trees will be constructed by the neighbor-joining method based on the Kimura 2-parameter distance matrix listed in the MEGA software. Bootstrap values greater than 750 of 1,000 replicates are considered significant.