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Determining the impact of opioid substitution therapy upon mortality and recidivism among prisoners: A 22 year data linkage study

Image: NDARC technical report cover
Author: Natasa Gisev, Sarah Larney, Jo Kimber, Lucy Burns, Don Weatherburn, Amy Gibson, Tim Dobbins, Richard Mattick, Tony Butler, Louisa Degenhardt

Resource Type: Technical Reports

NDARC Technical Report No. 330 (2014)
Prisoners experience very high rates of drug dependence, health problems and premature mortality. Without intervention they are highly likely to come into further contact with the criminal justice system, creating further health risk. Opioid dependence is a common problem among prisoners, and opioid substitution therapy (with methadone and buprenorphine) for opioid dependence may be an effective intervention in preventing morbidity, mortality and offending. Using retrospective data linkage, this study evaluated engagement with treatment, patterns of offending, incarceration and mortality among opioid-dependent people who received OST in New South Wales, Australia, at some time between 1985-2010. We linked all OST records with data on all court appearances 1993-2011, custody episodes 2000-2012, and mortality 1985-2012.
A total of 638,545 charges were laid against cohort members between 1993-2011. Eight in ten males (79.7%) and 67.9 percent of females had at least one charge; rates were 94.15 per 100 PY (95% CI 93.89-94.41) among males, and 53.19 per 100 PY (95% CI 52.91-53.46) among females, and highest at 15-19 years (175.74 per 100 PY males (95% CI 174.45-177.03), 75.60 per 100 PY females (95% CI 74.46-76.76)) and 20-24 years (144.61 per 100 PY males (95% CI 143.70-145.53), 84.50 per 100 PY females (95% CI 83.53-85.48)). The most frequent charges were theft (24.5% of all charges), traffic/vehicle offences (16.3%), offences against justice procedures (10.5%), illicit drug offences (10.0%), intentional injury offences (9.9%) and public order offences (8.9%).
Almost four in ten of the cohort (37%; 43% of men and 24% of women) had at least one episode of incarceration between 2000-2012. Men had a median of 3 (ranging between 1-47) incarcerations, and women, 2 (ranging between 1-35). Costs of incarceration of this cohort between 2000 and 2012 totalled nearly AUD$3 billion. Our findings suggest that a substantial minority of opioid dependent people experience incarceration, usually on multiple occasions and at significant cost.
Of the 34,962 people in the cohort, 6,830 were Indigenous and 28,132 were non-Indigenous. Among the 6,830 Indigenous people, 4,615 (67.6%) were male and 2,215 (32.4%) female. The median number of charges against Indigenous people (25, IQR 31) was significantly greater than non-Indigenous people (9, IQR 16) (p<0.001). The median proportion of follow-up time that Indigenous males and females spent in custody was twice that of non-Indigenous males (21.6% vs. 10.1%, p<0.001) and females (6.1% vs. 2.9%, p<0.001). The proportion of Indigenous people who first commenced OST in prison (30.2%) was three times that of non-Indigenous people (11.2%) (p<0.001).
Following on from our study of patterns of offending among opioid-dependent people, we also examined the effect of OST treatment and retention on crime rates among 10,744 opioid-dependent people who first entered OST on or after 1 January 2004. This allowed a comparison of crime rates in the four years immediately prior to treatment entry (the average time before an individual enters treatment after becoming opioid dependent), as well as periods in and out of OST after initiating treatment. We adjusted for time spent in custody over this period.
The crude crime rate (CCR) per 100 person-years for all offences that individuals were charged with prior to treatment entry was 130.78 (95% CI 129.65-131.91). A 32% reduction was observed while individuals were in OST [CCR per 100PY 88.29, 95% CI 86.96-89.63] and a 20 percent reduction was observed while individuals were out of OST [CCR per 100PY 101.67, 95% CI 100.35-102.99]. When comparing the crime rates after treatment entry only, being out of treatment was associated with a 15% increase, compared to the ratre during time spent in treatment.
We found that cohort members were in prison for 30,998 person-years (PY), during which time there were 51 deaths. The all-cause crude mortality rate (CMR) in prison was 1.6 per 1,000 PY (95% CI: 1.2, 2.2 per 1,000 PY), and the unnatural death CMR was 1.1 per 1,000 PY (95% CI: 0.8, 1.6 per 1,000 PY). Compared to prison time spent out of OST, the hazard of all-cause death was 74 percent lower while in OST in prison (adjusted hazard ratio (AHR): 0.26; 95% CI: 0.13 to 0.50), and the hazard of unnatural death was 87 percent lower while in OST (AHR: 0.13; 95% CI: 0.05 to 0.35). Compared to periods not in OST, the hazard of all-cause death during the first four weeks of incarceration was 94% lower while in OST (AHR: 0.06; 95% CI: 0.01 to 0.48).
There were 100,978 person-years of follow-up post-release, during which time 1,050 deaths occurred, for a CMR of 10.4 per 1000 person-years (95% CI: 9.8-11.0). Accidental drug-induced deaths were the most common cause of death. OST exposure in the four weeks post-release reduced the hazard of death by 75% (adjusted hazard ratio 0.25; 95%CI: 0.15, 0.52); OST receipt in prison had a short-term protective effect that decayed quickly across time.
Through the use of a population-wide linkage we were able to avoid the limitations of small, selected and possible unrepresentative samples. Our study provides persuasive evidence that OST provision in prison and post-release reduces mortality risk in the immediate post-release period. We concluded that OST in prison and post-release reduces mortality risk in the immediate post-release period. OST in prison should be scaled up, and post-release OST continuation maximised.