This poster, presented by Eron and colleagues, offers discouraging news in two areas. While this was a small pilot study, it sends a clear message. First, the findings suggest that potent combination therapy, even with a protease inhibitor, is not as effective in the genital tract as it is in the bloodstream. Second, the data suggest that drug-resistant strains of HIV could be transmitted via sexual contact, even in the presence of potent antiretroviral therapy.

Over a period of more than a year, the investigators analyzed blood and semen samples in nine HIV-positive men, collecting samples before the patients began combination therapy and during their treatment. Eron et al. concluded the following:

1. HIV that was resistant to both nucleoside (AZT, 3TC, ddC, etc.) and non-nucleoside (nevirapine, delavirdine) treatments was found in the semen of men with detectable virus in blood and semen.

2. Patterns of drug resistance in blood and in semen were similar, but not usually the same. In fact, the resistance patterns matched only once.

3. The majority of HIV in the genital tract is genetically different from the types of HIV found in the blood. This suggests that HIV evolves differently in each 'compartment', thus complicating treatment and efforts to prevent transmission of resistant virus.

4. Transmission of reverse transcriptase inhibitor-resistant -- and probably protease inhibitor-resistant -- virus is likely.

These data show that transmission and treatment of drug resistant HIV is likely to become a significant public health challenge for the HIV community. Larger studies are underway at a number of centers.