Identification of a Syndemic of Blood-Borne Disease Transmission and Injection drug Use Initiation at the US-Mexico Border.

Background: Efforts to prevent injection drug use (IDU) are increasingly focused on the role that people who inject drugs (PWID) play in the assistance with injection initiation. We studied the association between recent (ie, past 6 months) injection-related HIV risk behaviors and injection initiation assistance into IDU among PWID in the US-Mexico border region. Setting: Preventing Injecting by Modifying Existing Responses (PRIMER) is a multicohort study assessing social and structural factors related to injection initiation assistance. This analysis included data collected since 2014 from 2 participating cohorts in San Diego and Tijuana. Methods: Participants were 18 years and older and reported IDU within the month before study enrollment. Logistic regression analyses were conducted to assess the association between recent injection-related HIV risk behaviors (eg, distributive/receptive syringe sharing, dividing drugs in a syringe, and paraphernalia sharing) and recent injection initiation assistance. Results: Among 892 participants, 41 (4.6%) reported recently providing injection initiation assistance. In multivariable analysis adjusting for potential confounders, reporting a higher number of injection-related risk behaviors was associated with an increased odds of recently assisting others with injection initiation (adjusted odds ratio per risk behavior: 1.3; 95% confidence interval: 1.0 to 1.6, P = 0.04). Conclusions: PWID who recently engaged in one or more injection-related HIV risk behavior were more likely to assist others in injection initiation. These results stress the syndemic of injection initiation and risk behaviors, which indicates that prevention of injection-related HIV risk behaviors might also reduce the incidence of injection initiation.