title: Cross-border drug injection relationships among injection drug users in Tijuana, Mexico.
abstract: BACKGROUND
  International borders are unique social and environmental contexts characterized by high levels of mobility. Among drug users, mobility increases risk for human immunodeficiency virus (HIV) in part through its effects on the social environment. However, the social dynamics of drug users living in border regions are understudied.
  
  
  METHODS
  1056 injection drug users (IDUs) residing in Tijuana, Mexico were recruited using respondent-driven sampling (RDS) from 2006 to 2007, and underwent surveys and testing for HIV, syphilis, and tuberculosis (TB). Using logistic regression on baseline data, we identified correlates of having ever injected drugs with someone from the US.
  
  
  RESULTS
  Almost half (48%) reported ever injecting drugs with someone from the US. In RDS-adjusted logistic regression, factors independently associated with having ever injected with someone from the US included: having greater than middle school education (Adjusted Odds Ratio [AOR] 2.91; 95% confidence interval [C.I.] 1.52, 5.91), speaking English (AOR 3.24, 95% C.I. 1.96, 5.36), age (AOR 1.10 per year; 95% C.I. 1.07, 1.14), age at initiation of injection drug use (AOR 0.90 per year; 95% C.I. 0.86, 0.94), homelessness (AOR 2.61; 95% C.I. 1.27, 5.39), and having ever been incarcerated (AOR 11.82; 95% C.I., 5.22, 26.77). No associations with HIV, syphilis, TB, drug use, or injection risk behavior were detected.
  
  
  CONCLUSIONS
  Findings suggest that IDU networks in Mexico and the US may transcend international borders, with implications for cross-border transmission of infectious disease. Binational programs and policies need to consider the structure and geographic distribution of drug using networks.
authors.affiliation: Division of Global Public Health, Department of Medicine, University of California San Diego, 9500 Gilman Drive MC 0507, La Jolla, CA 92093-0507, USA. kdwagner@ucsd.edu
authors.forename: Karla D
authors.initials: KD
authors.lastname: Wagner
authors.forename: Robin A
authors.initials: RA
authors.lastname: Pollini
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Patterson
authors.forename: Remedios
authors.initials: R
authors.lastname: Lozada
authors.forename: Victoria D
authors.initials: VD
authors.lastname: Ojeda
authors.forename: Kimberly C
authors.initials: KC
authors.lastname: Brouwer
authors.forename: Alicia
authors.initials: A
authors.lastname: Vera
authors.forename: Tyson A
authors.initials: TA
authors.lastname: Volkmann
authors.forename: Steffanie A
authors.initials: SA
authors.lastname: Strathdee
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007398:Interpersonal Relations; D008297:Male; D008800:Mexico; D012307:Risk Factors; D012309:Risk-Taking; D012749:Sexually Transmitted Diseases / Q000150:complications / Q000523:psychology*; D015819:Substance Abuse, Intravenous / Q000150:complications / Q000523:psychology*; D014481:United States