Date of Award

January 2016

Document Type

Open Access Thesis

Degree Name

Master of Public Health (MPH)

Department

School of Public Health

First Advisor

Robert Heimer

Abstract

Aims: We sought to determine if age of first substance initiation (alcohol intoxication, marijuana use, pharmaceutical opioid use, polysubstance) was associated with faster rates of transition to injection drug use or heroin use. Subsequently, we examined if transition time was a predictor for hepatitis C infection.

Methods: From 2008-2012, 462 active injection drug users were recruited using respondent-driven sampling. Participants were interviewed about their injection-associated risk, and serological testing of HIV, HCV and HBV was performed. Kaplan-Meier analyses were used to examine the rate of transition from first substance event to initiation of heroin use or first injection. A Cox proportional hazards regression model was used to examine risk of transition, and regression analysis was performed to assess transition time as a predictor of HCV infection.

Results: Age of initiation was categorized into young and old based on the median age of the specific substance. Individuals initiating alcohol intoxication, marijuana use, and polysubstance use at older ages had faster transitions to both heroin and injection drug use. Younger pharmaceutical opioid initiates did not have significantly different transition times than older initiates, although the risk of early transition to heroin (AHR=1.7; 95% CI=1.3-2.3) and injection drugs (AHR=2.3; 95% CI=1.7-3.2) was significantly greater in older initiates. The adjusted odds of HCV infection decreased with increasing transition times to injection from initiation of opioid use by 9%, of polysubstance use by 13%, of marijuana use by 9%, and of alcohol intoxication by 8%.

Conclusions: Older initiates of pharmaceutical opioids, alcohol intoxication, and marijuana use are at greater risk of early transition to heroin use and injection of any drug than younger initiates, but initiate heroin use and injection at similar ages. Effective prevention strategies aimed at delaying transition to heroin use and injection drug use, particularly in older initiates, are needed to prevent incident HCV infections in this nonurban injection drug user population.

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This is an Open Access Thesis.

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