Overlap Of Syphilis And HIV Among Idu: A Mutlilevel Analysis

Melanie Lena Anne Rusch, University of California, San Diego
Basic-Applied Clinical

The goal of this proposal is to characterize the epidemiology of HIV and syphilis among injecting drug users (IDUs) in Tijuana, with respect to individual, social network and geographic factors. The main training objective is to increase the candidates' skills in social network analysis and geographic information systems (GIS) as they apply to HIV/STI epidemiology. Practical application of these skills will be obtained through modeling individual, network and geographical aspects of syphilis and HIV transmission among IDUs in Tijuana participating in 'Proyecto El Cuete', a prospective cohort of IDUs established by the primary mentor, Dr. Steffanie Strathdee. Specific aims are as follows: 1) to characterize the overlapping epidemiology of infectious syphilis and HIV among IDUs in Tijuana, based on risk factors at the individual level (sex trade, MSM, needle sharing, HIV status, travel to U.S.), network level (network size and needle sharing of recruitees, HIV-positivity of network, U.S. citizens in sexual or drug network), and neighborhood level (social disadvantage, distance from border, density of sex trade venues, density of health clinics); and 2) to develop a GIS database to incorporate high-risk venues (e.g., shooting galleries, sex trade environments), potential U.S. client venues (e.g. tourist bars) and structural factors (e.g. health clinics, distance to border) to examine the relationship between spatial characteristics and the distribution of infectious syphilis and syphilis/HIV co-infection. Syphilis is an important co-factor for HIV, increasing the potential for a more widespread epidemic. Prevalence of syphilis and HIV infections are increasing among IDU and female sex workers in Tijuana, Mexico, which is adjacent to San Diego, and there is growing concern about the potential for cross-border transmission of both HIV and syphilis. Given that California abuts the U.S.-Mexico border and that there is a high volume of bi- directional cross-border mobility, understanding the individual and contextual risks for HIV and syphilis and informing programs to reduce these risks is relevant for both Mexico and the U.S. As part of the 'Proyecto El Cuete', IDUs have been recruited through respondent-driven sampling techniques and are being prospectively followed-up every 6 months for 18 months. Syphilis and HIV testing are being done at each study visit, with free medical care being provided for positive cases through the Mexican healthcare system. Questionnaire items include individual drug and sexual risk behaviors, injection drug networks and information regarding where drugs are used. For the current proposal, the applicant will expand on the existing survey to include sexual risk venues and treatment locations. A multi-level modeling approach will be used to assess and compare the impact of individual risk behaviors (drug and sex risk), social and injection networks (network composition, risk of network members) and geographic risks (neighborhood-level risks, density of 'hot spots') on syphilis incidence and HIV co-infection with HIV. Overlap between networks and spatial clusters of syphilis and HIV will also be explored through a combination of model-based comparisons and spatial statistics. This study will position the candidate to be an independent researcher focusing on HIV/STI interactions with expertise on social network and GIS analysis, and will provide her with necessary skills for developing future HIV/STI interventions.