An Examination of Spatial Concentrations of Sex Exchange and Sex Exchange Norms Among Drug Users in Baltimore, Maryland

Baltimore, Maryland, consistently ranks highest nationally in rates of sexually transmitted diseases and sexually transmitted infections (STDs/STIs) and human immunodeficiency virus (HIV) infection. Prior studies have identified geographic areas where STI and HIV infection in the city is most prevalent. It is well established that sex exchange behavior is associated with HIV and STIs, yet it is not well understood how sex exchangers are spatially distributed within the high-risk areas. We sought to examine the spatial distribution of individuals who report sex exchange compared to those who do not exchange. Additionally, we examined the spatial context of perceived norms about sex exchange. Data for the study came from a baseline sample of predominately injection drug users (n = 842). Of these, 21 percent reported sex exchange in the prior ninety days. All valid baseline residential addresses of recruited participants living within Baltimore City boundaries were geocoded. The multidistance spatial cluster analysis (Ripley's K-function) was used to separately calculate the K-functions for the addresses of recruited participants reporting sex exchange versus non-sex exchange. Evidence of spatial clustering of sex exchangers was observed and norms aligned with these clusters. Of particular interest was the high density of sex exchangers in one specific housing complex of East Baltimore, which happens to be the oldest in Baltimore. These findings can inform targeted efforts for screening and testing for HIV and STIs and placement of both individual and structural-level interventions that focus on increasing access to risk reduction materials and changing norms about risk behaviors.