Effect of Antiretroviral Therapy on Transmission Dynamics| Area or behavior affected | Treatment effects expected to decrease transmission | Treatment effects expected to increase transmission |
| Viral load | Decreased infectiousness of the treated partner is substantial even with monotherapy (Musicco and others 1994). Transmission after exposure to individuals with a viral load of less than 1,500 copies per milliliter is extremely rare (Quinn and others 2000). No cases of sexual transmission from a partner with undetectable viremia have been reported. | As survival increases, the incidence of exposure to partners with HIV infection may increase (Hammer and others 1997). |
| Prophylaxis | Decreased susceptibility may occur during postexposure prophylaxis (Cardo and others 1997). | None. |
| Drug resistance | Impaired fitness and decreased viral load during drug-resistant viremia (Deeks and others 2000) appear to allow persistent decreases in infectiousness even after drug resistance has occurred (Leigh Brown and others 2003). | Impaired virological responses to therapy in the person who is infected by a resistant virus may partially offset the beneficial effect on infectiousness (Little and others 2002; Grant, Kahn, and others 2002). However, primary infection with a resistant virus may also be associated with slower progression of the disease (Grant, Hecht, and others 2002). |
| Risk behavior | Treatment may provide incentives for HIV testing and counseling, which has been associated with decreased risk behavior and HIV incidence. The availability of treatment may reduce stigma directly, and also indirectly by increasing the visibility of people living with HIV/AIDS.SFTRETRisk reduction counseling during treatment programs may reduce risk behavior. | Decreased fear of HIV and disinhibition of risk behavior are possibilities (Katz and others 2002). Risk behavior by people who are sick and who recover their health status may increase (Stolte and others 2001). |
| Sexual networks | Decreased fear of HIV may foster more informed risk behavior, including increased use of testing and more thoughtful partner selection, including serosorting and sorting by risk level (McConnell and Grant 2003). | Decreased fear of HIV may disinhibit risk behavior, reduce serosorting, and increase mixing between higher- and lower-risk groups in the population. |
| Epidemiological | The effective prevalence of infectious people will decrease because of treatment effects on infectiousness or increased serosorting. | Treatment-induced reduction in mortality may increase the prevalence of infection, although many being treated will be less infectious or better informed regarding risk reduction strategies. A rebound of viral load with treatment failure may mean that treatment postpones transmission rather than reducing it. |
