Project Abstract Black men who have sex with men (MSM) in the South had the highest rate of new HIV diagnoses (48%) and the 2nd highest rate of HIV prevalence (31%) among MSM of all races in 2018. Furthermore, racial disparities exist in terms of viral suppression, with 52% of Black MSM living with HIV achieving viral suppression compared to 61% of White MSM. An extensive body of research has identified multiple co-occurring psychosocial factors and structural factors that contribute to racial disparities in HIV diagnoses, prevalence, and outcomes among Black MSM. This combination constitutes a syndemic, “the interaction of 2+ factors or health conditions” that increase HIV among Black MSM. At the same time, mounting evidence suggests social support as an effect modifier of viral suppression among Black MSM experiencing a syndemic. To date, no study has sought to identify the subgroups of Black MSM living with HIV in Florida who could benefit from a shared biobehavioral HIV intervention to improve social support and viral suppression based on their shared characteristics. Therefore, the overarching goal of the K01 award is to provide me with the resources, training, mentoring and knowledge needed to examine the intersectionality of public health, substance use and HIV, and syndemic research. In this proposal, I will employ the explanatory sequential mixed method design to accomplish the specific aims which include: 1a) application of latent class analyses (LCA) for the identification of heterogeneous syndemic classes among Black MSM living with HIV; 1b) expansion of existing literature to examine the association between syndemic classes and demographics; 2) validation of syndemic classes on scales assessing social support; 3) exploration of syndemic class group differences on measures of baseline level and one-year change in viral suppression; and 4) application of semi-structured interviews to validate and contextualize quantitative findings. These goals will be accomplished by leveraging existing data, participants, and resources from an ongoing NIAAA-funded observational longitudinal study (U24AA022002) and interviewing a sample of 20 Black MSM living with HIV in Florida. This K01 application will build on my expertise in HIV outreach, public health, qualitative research, and clinical intervention research related to substance use and HIV with advanced training in: applying a syndemic framework to Black MSM, using LCA to model syndemic conditions among Black MSM, recruiting Black MSM into biobehavioral HIV research, identifying effective biobehavioral HIV interventions and strategies to improve social support and viral suppression among this population, and responsible conduct of research. Overseeing this training are a diverse and interdisciplinary team of mentors, each of whom will bring unique areas of expertise and years of collaboration: Drs. Robert Cook and Eric Schrimshaw (co-primary mentors) and Drs. Typhanye Dyer, Mattia Prosperi, Mic...