title: Transitions to injecting drug use among noninjecting heroin users: social network influence and individual susceptibility.
abstract: OBJECTIVE
  To determine the incidence/predictors of transitions to injecting among noninjecting heroin users (NIUs).
  
  
  METHODS
  Street-recruited NIUs in New York City, March/1996-March/2003, were interviewed for a prospective cohort study about social network influence (communication promoting injecting; exposure to injectors) and individual susceptibility. A transition to injecting was the first drug injection following baseline. Hazards ratios (HRs) (P < 0.05) were estimated by Cox proportional hazards regression, stratified by baseline injecting history.
  
  
  RESULTS
  Of 369 (64% of 579) followed, former-injectors were more likely to transition to injecting (33% or 53/160 vs. 12% or 25/209; 16.0/100 person-years-at-risk [pyar] vs. 4.6/100 pyar; HR = 3.25). Independent predictors among never-injectors included using > or =2 bags of heroin daily (HR = 7.0); social network influence (communication) and homelessness (HR = 6.3); shorter-term heroin use (HR = 5.3); social network influence (exposure) and physically abused (HR = 4.7); friends approve/condone drug injecting (HR = 3.5); lower perceived social distance from injectors (HR = 2.9); and younger age at first heroin use (HR = 1.2). Independent predictors among former-injectors were social network influence (communication) and lower perceived social distance from injectors (HR = 3.4); white race/ethnicity (HR = 2.0); not very afraid of needles (HR = 1.8); and younger age (HR = 1.1).
  
  
  CONCLUSIONS
  The risk of initiating injecting was lower than the risk of resuming injecting. Social network influence facilitates transitioning to injecting among those susceptible. Interventions to prevent injecting should address both social network influence and individual susceptibility.
authors.affiliation: Institute for International Research on Youth at Risk, National Development and Research Institutes, Inc., New York, NY 10010, USA. neaigus@ndri.org
authors.forename: Alan
authors.initials: A
authors.lastname: Neaigus
authors.forename: V Anna
authors.initials: VA
authors.lastname: Gyarmathy
authors.forename: Maureen
authors.initials: M
authors.lastname: Miller
authors.forename: Veronica M
authors.initials: VM
authors.lastname: Frajzyngier
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Friedman
authors.forename: Don C
authors.initials: DC
authors.lastname: Des Jarlais
mesh_terms: D000328:Adult; D000367:Age Factors; D015331:Cohort Studies; D005260:Female; D006556:Heroin Dependence; D006703:Ill-Housed Persons; D006801:Humans; D015994:Incidence; D008297:Male; D009519:New York City; D011446:Prospective Studies; D012931:Social Environment; D013223:Statistics as Topic; D015819:Substance Abuse, Intravenous / Q000453:epidemiology*; D013997:Time Factors