PROJECT SUMMARY Despite the significant advances in HIV antiretroviral therapies for effective treatment and prophylaxis regimens, young Black men and transwomen in North Carolina (NC) continue to be affected by HIV at nearly the same rates over the last 10 years. The new diagnosis rate in NC for Black men aged 13-24 years was 104.7/100k population in 2009 and 114.6/100k population in 2019. Viral suppression failures lead to higher rates of uncontrolled HIV in the sexual networks of young Black men who have sex with men (YBMSM). YBMSM who are HIV-negative are significantly less likely to be on pre-exposure prophylaxis (PrEP), especially in states which have not or have only recently expanded Medicaid. There are both clinical and public health points of intervention where YBMSM could be given greater access to PrEP. Clinical guidelines indicate PrEP based on individual-level risk factors (e.g., bacterial diagnosis) or on partner-level risk factors (e.g., HIV+ partner). However, YBMSM are more likely to be part of a sexual network where both HIV and bacterial sexually transmitted infections are circulating. If using the concept of “degrees of separation”, YBMSM in the US South tend to be fewer degrees away from someone with HIV, so accounting only for their person-level or first degree partner-level risk factors fails to place the person in context. Clinically, an understanding of the partners of the partners may turn out to be an indicator for PrEP that is not currently assessed. From a public health standpoint, PrEP can benefit not only the person taking it but also the larger community if preventing one person’s infection also protects future partners. It can thus have a positive effect across the sexual network, as has been demonstrated by simulation studies. As resources to provide PrEP are extremely limited, identifying network members who would themselves benefit from PrEP and whose partners would benefit as a result is key. These gaps suggest that to better assess HIV risk – and recommend prophylaxis – an understanding of risk within the entire sociosexual network is needed as the individual-level risk is a product of the local network beyond just partners. In this project, we aim to quantify the additional risk of HIV among YBMSM who are positive for syphilis or who are partners of someone positive for syphilis compared to the risk among other demographic groups and to develop a model that can be applied at the time of the public health interview to predict HIV seroconversion within 3 years. We also aim to test methods to scale up to the underlying transmission network using the subset of relationships which are observed during public health interactions.