Written by Chris Pilcher, MD

Susan Little from San Diego [Abstract 756] reported a hugely important study that surveyed phenotypic resistance (defined as a >10 fold decrease in susceptibility to any drug) in 108 newly infected patients in North American cities (Birmingham, Dallas, Denver, Los Angeles, San Diego, Seattle, Montreal and Vancouver) and found an overall prevalence of 8% resistance, with 4% being resistant to two classes. What was more worrisome, they noted that the overall rate of resistance has increased markedly between the 1995-8 period and 1999-2000 (from 3 to 14%; 1 to 6% for NNRTIs and 1 to 7% for PIs). Little and colleagues were able to pool data from enough patients to show that the presence of this resistance (>10 fold to any ARV) did increase the risk of virologic failure on therapy for all comers. In abstract 404 Little reported that 4/14 (29%) with >2.5 fold resistance experienced virologic failure (lack of suppression or relapse) compared to 1/34 (3%) who had no resistance. Although most clinicians do not routinely take these type of data into account except when dealing with patients that have primary infection, it is critical to remember that burgeoning resistance today could have significant implications for success of antiretroviral therapy for chronically infected individuals when they are diagnosed years from now-since their bodies will still harbor resistant viruses from the time of their infection today. The issue is clearly not going to go away in the years to come, as more and more people living with HIV and potentially transmitting virus begin to fail more and more regimens with more and more drugs.

Among 61 newly-HIV infected persons from New York City and Montreal (Canada) in 1999-2000, 26% had primary gene mutations (drug resistance) in HIV protease and reverse transcriptase (7% in protease alone), representing an increase from 16% in the same location during 1995-1998 (abstract 423). The lead author was Dr. V. Simon of the Aaron Diamond AIDS Research Center in New York City. The results have direct implications regarding newly transmitted HIV infection and potentially ineffective HAART regimens for patients in those locations.