Stable and low prevalence of transmitted HIV type 1 drug resistance despite two decades of antiretroviral therapy in Hong Kong.

Transmitted HIV resistance is of both clinical and public health importance. Baseline genotypic resistance testing was performed for HIV-1-infected treatment-naive patients who were newly diagnosed between 2003 and 2007 and attended the government HIV clinic in Hong Kong. International AIDS Society-USA mutation figures and the Stanford resistance interpretation algorithm were used to identify resistance mutations and drug susceptibility, respectively. The pattern and factors associated with resistance were examined. The presence of one or more IAS-USA resistance mutations was found in 26 (3.6%) of 731 patients over the 5-year study period. Overall, protease inhibitor (PI) resistance mutations were most common (16), followed by nucleoside reverse transcriptase inhibitors (NRTIs) (8) and nonnucleoside reverse transcriptase inhibitors (NNRTIs) (3). Resistance to drugs in one, two, and three classes was present in 25 (3.4%), 1 (0.1%), and 0, respectively. Seventy-eight (10.7%) had strains of reduced susceptibility, as predicted by the Stanford algorithm to display at least low-level resistance to one or more drugs of the three classes. Intermediate or high-level resistance was found in 1.6% overall, and in descending order for NRTIs, PIs, and NNRTIs. There was no temporal trend of increase in resistance. Sex between men, Chinese ethnicity, and lower baseline CD4 were associated with harboring resistant strains as elucidated by either method. We conclude that transmitted HIV-1 drug resistance is uncommon in up to two decades of antiretroviral therapy in Hong Kong. The situation has to be continually monitored for any change in significance.