title: Characteristics of people who initiate injection drug use later in life.
abstract: BACKGROUND
  Studies report that among people who inject drugs (PWID), approximately 1 in 7 initiated injection during their thirties or later (referred to hereafter as "late initiates"). However, little is known about individuals who are late initiates. This study aims to describe characteristics of late initiates to drug injection and to examine how they differ from people who initiated drug injection prior to the age of 30 ("typical initiates").
  
  
  METHODS
  We recruited 696 active PWID in Los Angeles and San Francisco, California between 2011 and 2013, using targeted sampling and street outreach methods. Participants completed personal interviews that covered items on demographics, drug use history and practices, injection initiation episode, HIV injection- and sex-related risk, health care utilization among others. We used bivariate and multivariate analyses to examine factors associated being a late initiate.
  
  
  RESULTS
  In our sample, 19% of participants who were 30 years or older were classified as late initiates. In multivariate analysis controlling for city, late initiates had higher odds of being female and African American, having been in treatment prior to initiation, initiating illicit drug use at an older age, and being assisted into injection by someone of the same age or younger. Late initiates had lower odds of frequent recent injection, and having a bipolar disorder diagnosis.
  
  
  CONCLUSIONS
  Late initiates comprise a significant proportion of active PWIDs. More study on the health consequences of late initiation are needed as are interventions to prevent transition to drug injection among at-risk populations.
authors.affiliation: Global Forum on MSM and HIV, 436 14th Street, Suite 1500, Oakland, CA 94612, United States. Electronic address: ArreolaResearch@gmail.com.
authors.forename: Sonya
authors.initials: S
authors.lastname: Arreola
authors.affiliation: Department of Preventive Medicine, Institute for Prevention Research, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, United States.
authors.forename: Ricky N
authors.initials: RN
authors.lastname: Bluthenthal
authors.affiliation: Urban Health Program, RTI International, 351 California St., San Francisco, CA 94104, United States.
authors.forename: Lynn
authors.initials: L
authors.lastname: Wenger
authors.affiliation: Department of Preventive Medicine, Institute for Prevention Research, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Chu
authors.affiliation: Department of Preventive Medicine, Institute for Prevention Research, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089, United States.
authors.forename: James
authors.initials: J
authors.lastname: Thing
authors.affiliation: Urban Health Program, RTI International, 351 California St., San Francisco, CA 94104, United States.
authors.forename: Alex H
authors.initials: AH
authors.lastname: Kral
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000375:Aging / Q000523:psychology*; D003430:Cross-Sectional Studies; D005260:Female; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D015141:Los Angeles / Q000453:epidemiology; D008297:Male; D010342:Patient Acceptance of Health Care / Q000523:psychology; D012307:Risk Factors; D012495:San Francisco / Q000453:epidemiology; D015819:Substance Abuse, Intravenous / Q000453:epidemiology* / Q000523:psychology*; D055815:Young Adult
keywords: Aging; Epidemiology; Injection drug users; Injection initiation; People who inject drugs; Substance use