Changes in the transmission dynamics of the HIV epidemic after the wide-scale use of antiretroviral therapy could explain increases in sexually transmitted infections -: Results from mathematical models

Background: Recent increases in bacterial sexually transmitted infections (STI) and risk behavior have coincided with the introduction of antiretroviral therapy (ART) in homosexual communities of industrialized countries. The reasons for these increases are not fully understood. Goal: The goal of this study was to understand the various effects of ART on risk behaviors and STI. Objective: The objective of this study was to assess the independent impact of the change in the transmission dynamics of HIV/AIDS as a result of the wide-scale use of ART on a bacterial STI. Study Design: We developed a mathematical model of bacterial STI and treated/untreated HIV/AIDS infection for an open homosexual population. At the individual level, we assume that susceptible and healthy HIV-positive individuals do not increase their risk behavior as a result of ART over time. However, individuals with AIDS, who are successfully treated with ART, can resume sexual activity. The impact of the wide-scale use of ART on risky behavior, STI, and HIV/AIDS was evaluated over a wide range of assumptions on treatment use, ART efficacy, and population characteristics. Results: Over 10 years, 0% to 55% new bacterial STI could be attributed to the wide-scale use of ART as a result of more modest increases (0-25%) in risky sex occurring at the population level rather than at the individual level. These increases have a negative impact on HIV if coverage is too low. Increasing treatment coverage helps to prevent more HIV infections despite larger increases in risky sex and STI that is predicted to ensue. Conclusion: Taking the differential impact of wide-scale use of ART into account helps to interpret recent behavioral and STI trends. Our results have implications for prevention strategies and for the formulation of public health policies. A better understanding of the differential impact of ART on sexual network over time is required.