Background:  The prevalence of drug resistance among new HIV infections is increasing. The presumed source of new resistant infections is HIV⁺ patients receiving antiretroviral therapy (ART) who engage in behaviors that transmit HIV. Little is known about the risk behaviors of these patients, potential partners exposed and relationship of these to ART resistance. Our objective was to define and characterize risk of sexual transmission of resistant HIV among HIV⁺ patients in clinical care.

Methods:  We designed a longitudinal study of 395 HIV⁺ patients receiving care from 2000-2002, and collected self-reported HIV sexual risk behavior and HIV genotypic resistance data.

Results:  At baseline 333 HIV⁺ patients had HIV genotypic and transmission risk behavior data available; 75 (23%) had had unprotected sex during the previous 3 months, resulting in 1126 unprotected sexual events with 191 partners. Of these, 18 (24%) had resistant HIV and 207 unprotected sexual events, exposing 31 partners. Unprotected sexual behavior was not related to viral load or HIV resistance status. At 6 months, among 248 patients with behavioral and HIV genotypic data, 35 (14%) engaged in 659 unprotected sex events, 14 with resistant HIV (8 of whom did not have resistance and risk at baseline), who had 324 unprotected events with 22 partners. The proportion of patients whose risk behavior decreased over 6 months (23% to 14%, p = 0.01) but among patients with risk the proportion of those with resistant HIV increased (24% to 40%, p = 0.085) and the proportion of unprotected sexual events involving resistant virus increased from 18% to 49%, p <0.001. Thus, through 6 months of observation, 26/395 (7 %) patients both had resistant HIV and engaged in unprotected sex with a minimum of 531 unprotected sexual events (30% of all unprotected events) exposing a minimum of 31 to 53 partners to resistant HIV.

Conclusions:  A minority of patients in clinical care engage in HIV sexual transmission risk behavior with resistant HIV. But this core group (~7% of all patients) had very large numbers of unprotected sex events, exposing substantial numbers of at-risk partners to resistant HIV. In addition, the proportion of unprotected sexual events involving resistant HIV increased over time. These data help explain the rising prevalence of new ART-resistant HIV infections and emphasize the need to include HIV transmission risk-reduction strategies in clinical care.

Keywords: Sexual Risk Behavior; HIV drug resistance