More than 50% of Spanish youth does not use of condoms correctly and consistently. University students are a particular population at high risk of the HIV infection, other STIs and unwanted pregnancies. The influence of psychological variables in using of condom is analyzed by gender and type of sexual relationship. A total of 256 females and 168 males were assessed (Mage= 20.62; SD = 2.16). A regression logistic analysis showed that sexual sensation seeking appears as an explanatory variable of inconsistently condom use in both females and males in vaginal intercourse, steady relationship intercourse and sex under the alcohol and other drugs effects (adjusted odds ratio between 1.095 and 1.124). Moreover, self-esteem appears as a risk factor and extraversion as a protective factor of use of condom in females. On the other hand, neuroticism reveals itself as a protective factor and fear of negative evaluation as a risk factor of use of condom in males. It is necessary to know the psychological mechanisms that underlie sexual risk behaviors for adapting interventions to individual and contextual characteristics.

We investigated how different models of HIV transmission, and assumptions regarding the distribution of unprotected sex and syringe-sharing events (‘risk acts’), affect quantitative understanding of HIV transmission process in people who inject drugs (PWID). The individual-based model simulated HIV transmission in a dynamic sexual and injecting network representing New York City. We constructed four HIV transmission models: model 1, constant probabilities; model 2, random number of sexual and parenteral acts; model 3, viral load individual assigned; and model 4, two groups of partnerships (low and high risk). Overall, models with less heterogeneity were more sensitive to changes in numbers risk acts, producing HIV incidence up to four times higher than that empirically observed. Although all models overestimated HIV incidence, micro-simulations with greater heterogeneity in the HIV transmission modelling process produced more robust results and better reproduced empirical epidemic dynamics.