title: Polydrug Use and HIV Risk Among People Who Inject Heroin in Tijuana, Mexico: A Latent Class Analysis.
abstract: BACKGROUND
  Although most people who inject drugs (PWID) in Tijuana, Mexico, primarily inject heroin, injection and non-injection use of methamphetamine and cocaine is common. We examined patterns of polydrug use among heroin injectors to inform prevention and treatment of drug use and its health and social consequences.
  
  
  METHODS
  Participants were PWID residing in Tijuana, aged ≥18 years who reported heroin injection in the past six months and were recruited through respondent-driven sampling (n = 1,025). Latent class analysis was conducted to assign individuals to classes on a probabilistic basis, using four indicators of past six-month polydrug and polyroute use: cocaine injecting, cocaine smoking or snorting, methamphetamine injecting, and methamphetamine smoking or snorting. Latent class membership was regressed onto covariates in a multinomial logistic regression.
  
  
  RESULTS
  Latent class analyses testing 1, 2, 3, and 4 classes were fit, with the 3-class solution fitting best. Class 1 was defined by predominantly heroin use (50.2%, n = 515); class 2 by methamphetamine and heroin use (43.7%, n = 448), and class 3 by methamphetamine, cocaine, and heroin use (6.0%, n = 62). Bivariate and multivariate analyses indicated a group of methamphetamine and cocaine users that exhibited higher-risk sexual practices and lower heroin injecting frequency, and a group of methamphetamine users who were younger and more likely to be female.
  
  
  CONCLUSIONS
  Discrete subtypes of heroin PWID were identified based on methamphetamine and cocaine use patterns. These findings have identified subtypes of heroin injectors who require more tailored interventions to reduce the health and social harms of injecting drug use.
authors.affiliation: a Division of Global Public Health, University of California, San Diego School of Medicine , La Jolla , California , USA.|b Graduate School of Public Health, San Diego State University , San Diego , California , USA.
authors.forename: Meredith C
authors.initials: MC
authors.lastname: Meacham
authors.affiliation: c Pacific Institute for Research and Evaluation , Calverton , Maryland , USA.
authors.forename: Abby E
authors.initials: AE
authors.lastname: Rudolph
authors.affiliation: a Division of Global Public Health, University of California, San Diego School of Medicine , La Jolla , California , USA.
authors.forename: Steffanie A
authors.initials: SA
authors.lastname: Strathdee
authors.affiliation: d Vancouver Island Health Authority , Victoria , British Columbia , Canada.
authors.forename: Melanie L
authors.initials: ML
authors.lastname: Rusch
authors.affiliation: a Division of Global Public Health, University of California, San Diego School of Medicine , La Jolla , California , USA.
authors.forename: Kimberly C
authors.initials: KC
authors.lastname: Brouwer
authors.affiliation: e Department of Psychiatry, University of California , San Diego, La Jolla , California , USA.
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Patterson
authors.affiliation: a Division of Global Public Health, University of California, San Diego School of Medicine , La Jolla , California , USA.
authors.forename: Alicia
authors.initials: A
authors.lastname: Vera
authors.affiliation: f El Colegio de la Frontera Norte , Tijuana , Mexico.
authors.forename: Gudelia
authors.initials: G
authors.lastname: Rangel
authors.affiliation: g Department of Psychology, San Diego State University , San Diego , California , USA.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Roesch
mesh_terms: D000328:Adult; D003042:Cocaine / Q000008:administration & dosage; D055030:Drug Users / Q000706:statistics & numerical data*; D005260:Female; D015658:HIV Infections / Q000453:epidemiology; D006556:Heroin Dependence / Q000145:classification / Q000453:epidemiology*; D006801:Humans; D016015:Logistic Models; D008297:Male; D008694:Methamphetamine / Q000008:administration & dosage; D008800:Mexico; D012307:Risk Factors; D012309:Risk-Taking; D017678:Sex Distribution; D015819:Substance Abuse, Intravenous / Q000145:classification / Q000453:epidemiology*; D047568:Unsafe Sex / Q000706:statistics & numerical data; D055815:Young Adult
chemical_list: D008694:Methamphetamine; D003042:Cocaine
keywords: HIV risk; Tijuana; latent class analysis; people who inject drugs; polydrug use