Utilization patterns and correlates of retention among clients of the needle exchange program in Baltimore, Maryland.

NEP effectiveness at a population level depends on several factors, including the number of injection drug users (IDUs) retained, or consistently accessing services. Patterns of retention in the Baltimore Needle Exchange Program (BNEP) from 1994 to 2006 were calculated using enrollment surveys and client records. We used Andersen's Behavioral Model of Health Services Use to frame our examination of factors associated with retention. Client retention was measured in two ways: whether a client returned to the exchange within 12 months of enrollment and how many times a client returned within these 12 months. BNEP clients (N=12,388) were predominantly male (69%), African-American (73%), and >or=age 30 (86%). Nearly two-thirds (64%) of clients returned within 12 months of their first BNEP visit. The median number of return visits per client within 12 months was one (IQR: 0-5). Young age (<30), being married, having an injection drug use history of less than 20 years, and living farther from the BNEP site were characteristics independently associated with both measures of low retention in multivariate analysis. Among younger injectors, geographical proximity was a particularly important predictor of retention. Further insight into the influence of these factors may help in developing programmatic changes that will be effective in increasing retention.