  The transmission through contacts among MSM (men who have sex with men) is
one of the dominating contributors to HIV prevalence in industrialized
countries. In Amsterdam, the capital of the Netherlands, the MSM risk group has
been traced for decades. This has motivated studies which provide detailed
information about MSM's risk behavior statistically, psychologically and
sociologically. Despite the era of potent antiretroviral therapy, the incidence
of HIV among MSM increases. In the long term the contradictory effects of risk
behavior and effective therapy are still poorly understood. Using a previously
presented Complex Agent Network model, we describe steady and casual
partnerships to predict the HIV spreading among MSM. Behavior-related
parameters and values, inferred from studies on Amsterdam MSM, are fed into the
model; we validate the model using historical yearly incidence data.
Subsequently, we study scenarios to assess the contradictory effects of risk
behavior and effective therapy, by varying corresponding values of parameters.
Finally, we conduct quantitative analysis based on the resulting incidence
data. The simulated incidence reproduces the ACS historical incidence well and
helps to predict the HIV epidemic among MSM in Amsterdam. Our results show that
in the long run the positive influence of effective therapy can be outweighed
by an increase in risk behavior of at least 30% for MSM. Conclusion: We
recommend, based on the model predictions, that lowering risk behavior is the
prominent control mechanism of HIV incidence even in the presence of effective
therapy.
