Evaluating the susceptibility to therapy of viral isolates obtained from 69 individuals from Boston, Dallas, Denver, Los Angeles and San Diego, Little and colleagues further demonstrate the rise of drug-resistant HIV transmission. In this study, all specimens were collected soon after virus exposure (an average of 79 days, range 0-239 days) from individuals who presented with primary HIV infection. The mean CD4 count in these individuals measured 548 and the mean RNA PCR measured 83,000 copies. The ViroLogic^TM assay was used to measure drug susceptibility of these isolates as compared to that of a control virus (NL4-3 virus), and was expressed as either moderate decreased susceptiblity (more than 2.5 to 10 times less susceptible to the drug compared to the contol virus) or major decreased susceptibility (more than 10 times less susceptible):

Oddly, most of the NNRTI resistant isolates came from participants in San Diego. However, resistance to all available NNRTIs, NRTIs and PIs were detected. Overall, reduced susceptibility to one or more drugs was seen in 28% in the study population, underscoring a need for continued emphasis of safe-sex practices, and making a stong case for the use of genotypic and phenotypic assays before instituting therapy in persons newly diagnosed with HIV infection.