Low prevalence of transmitted drug resistance among newly diagnosed HIV-1 patients in Latvia.

Transmitted drug resistance (TDR) is a concern because it may reduce the efficacy of antiretroviral treatment. Plasma samples of 119 HIV-1-infected patients who were newly diagnosed at the Infectology Center of Latvia in 2005 and 2006 were analyzed by an in-house genotypic resistance assay to determine the prevalence of TDR in Latvia. TDR was identified using the WHO 2009 list of mutations for surveillance of TDR as implemented in the Stanford Calibrated Population Resistance tool. Neighbor-joining phylogenetic analyses were used to determine genetic subtype and investigate the relatedness of the sequences. Resistance testing was successful in 117 of 119 patients. The study population represented ∼20% of all patients that were diagnosed in Latvia in 2005 and 2006 and was well distributed between gender, transmission routes, and areas of residence. Four patients showed evidence of TDR, which represents a prevalence of TDR of 3.4% (95% CI: 0.9-8.5%). All four patients displayed single, but different resistance mutations (M46I, F53L, M41L, and G190A). All patients, except one, were predicted to respond well to standard first-line therapy in Latvia. The prevalence of TDR in Latvia was low, which partly may be due to the low proportion of HIV-1 patients who receive antiretroviral therapy. The results indicate that routine resistance testing in Latvia currently should be focused on patients who display treatment failure, rather than treatment naive patients.