Increasing risk behaviour can outweigh the benefits of antiretroviral drug treatment on the HIV incidence among men-having-sex-with-men in Amsterdam

Table 2 Scenarios for simulating the HIV epidemic among MSM in Amsterdam (factors changed since 2006).

Scenario	Risk behavior factor	Treatment-induced infectivity reduction factor
Reference (RS)	1.30	Moderate
Prediction 1 (P1)	1.05*1.30	Moderate
Prediction 2 (P2)	1.05*1.30	Optimistic
Prediction 3 (P3)	1.10*1.30	Optimistic
Prediction 4 (P4)	1.20*1.30	Optimistic
Prediction 5 (P5)	1.30*1.30	Optimistic

The values of parameters change from 2006 onward in the simulations of scenarios. The risk behavior factor is a multiplicative factor of the transmission probability between two partners. For prediction scenarios, the value of the risk behavior factor is calculated by scaling the value in 2000-2005 (1.30 for both the HIV negative and positive, see Table 2 in [3]) to account for the increase in risk behavior after 2006. For example, an increase of 5% in risk behavior is assumed after 2006 for P1. The distributions of the moderate and optimistic treatment-induced infectivity reduction factors are listed in Table 1. All scenarios take a value of moderate treatment-induced infectivity reduction from 1985 to 2006.

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