I am Professor in the Department of Community Health Systems and the Division of Prevention Science at the University of California, San Francisco, and a Senior Research Scientist at the San Francisco Department of Public Health. I have been conducting research on the intersection between substance use (i.e., alcohol, methamphetamine, cocaine, and opioids), and HIV, and intervention research studies among key populations at risk for HIV (i.e., men who have sex with men [MSM], transgender individuals, and people who use drugs) for 15 years. My contributions to Science are summarized below:

1. A significant thread of my research has investigated the factors associated with HIV risk among key affected populations. I have published multiple articles that have demonstrated how a myriad of social, behavioral, and structural factors play a role in sustaining the HIV epidemic among men who have sex with men (MSM), transgender women, and people who use drugs. These publications describe how the co-occurrence of these factors may result in heightened risk for HIV and underscore the need for multi-level interventions that jointly address these “syndemic” conditions. Furthermore, I have published extensively on how stigma, discrimination, and criminalization impacts access to evidence-based interventions. Most recently, I also published one of the first global studies to document the disparate impact of COVID-19 on HIV prevention and treatment service accessibility among MSM who engage in sex work, were from immigrant backgrounds, were racial/ethnically minoritized, and who have lower socio-economic status in the journal AIDS and Behavior.

2. In addition to conducting epidemiologic studies on the determinants of HIV risk among key populations, I have actively engaged in the design and evaluation of interventions to address modifiable risk factors linked to HIV risk. In particular, I have conducted randomized-controlled, pharmacologic and behavioral intervention trials to reduce substance use and substance-associated sexual risk behaviors among key populations. I was the primary analyst in the first randomized, placebo-controlled trial that efficaciously reduced methamphetamine urine-positivity and methamphetamine-associated sexual risk behaviors in intention-to-treat analyses. Additionally, I was the lead author of the first article that have demonstrated the efficacy of Personalized Cognitive Counseling (PCC) in reducing alcohol and substance use among MSM—these findings has been included in the CDC’s Compendium of Evidence-Based Interventions and Best Practices for HIV Prevention. These studies are also unique because they have enrolled active-substance users who are not seeking substance use treatment and support the feasibility of conducting research based on harm-reduction principles.

3. I am also actively conducting research on the health outcomes among people living with HIV. In this capacity, I have examined outcomes along the HIV care continuum and evaluated predictors of linkage, retention and engagement in care, and virologic suppression. Additionally, I have published papers on the collateral benefits of ART initiation and the correlates of spontaneous HCV clearance using data from longitudinal cohort studies among people living with HIV. I was also involved in the seminal study that demonstrated the association between community viral load (i.e., a community's average level of HIV infectiousness) and newly diagnosed HIV infections. This paper, which has been cited 851 times, provided proof of concept data for the Treatment as Prevention (“TasP”) approach.

4. As a translational research scientist and epidemiologist, I have also endeavored to synthesize research findings across multiple studies. I conducted the first systematic review and meta-analysis on the efficacy of behavioral interventions on amphetamine-group substances, published on The Lancet. As the primary analyst in this paper, I created the fixed and random-effects models for the meta-analyses conducted in the review, which demonstrated that high-intensity behavioral interventions are efficacious in reducing methamphetamine in pooled analyses. I was also the lead author in a narrative review synthesizing the literature on non-injection substance use interventions among MSM. Most recently, I was the senior author in a narrative review on novel intervention to prevent HIV and Hepatitis C among people who inject drugs. Both narrative reviews provided an up-to-date account of the state of prevention science and highlighted the most promising interventions for substance users. Additionally, I published a meta-analyses on the psychometric properties of measures of substance use with collaborators from the HIV Prevention Trials Network.