The association of prison security level with mortality after release from prison: a retrospective national cohort study (2000-16).

Background: Incarceration might contribute to increased mortality in an already marginalised population. A better understanding of the prison-related factors that are associated with mortality is important for preventing the negative health consequences of incarceration. We aimed to investigate all-cause and cause-specific mortality following release from high-security and low-security prisons.

Methods: In this retrospective national cohort study, we used data from the Norwegian Prison Release study (nPRIS), which includes complete national register data for 96 859 individuals from the Norwegian Prison Register linked to the Norwegian Cause of Death Register from Jan 1, 2000, to Dec 31, 2016. The study cohort included all people in Norway released from a high-security or low-security prison unit. Cause of death was categorised into internal causes (infectious, cancerous, endocrine, circulatory, respiratory, digestive, nervous system diseases, and mental health disorders) and external causes (accidents, suicides, and homicides) according to the 10th revision of the International Classification of Diseases. We calculated crude mortality rates (CMR) and estimated Cox proportional-hazards models.

Findings: There were 151 790 releases in the study period (68·4% from low-security and 31·6% from high-security prisons) from 91 963 individuals. The overall CMR was 854·4 [95% CI 834·7-874·2] per 100 000 person-years (436·2 [422·1-450·3] per 100 000 person-years for internal causes and 358·3 [345·5-371·1] per 100 000 person-years for external causes). The overall post-release mortality rate was higher in those released from high-security prisons (1142·5 [95% CI 1102·6-1182·5] per 100 000 person-years) than in those released from low-security prisons (714·6 [692·6-736·6] per 100 000 person-years). Our results suggest an association between release from high-security prisons and elevated mortality due to both external causes (adjusted hazard ratio [aHR] 1·75 [95% CI 1·60-1·91]) and internal causes (1·45 [1·33-1·59]), compared to release from low-security prisons.

Interpretation: Imprisonment and the post-release period can be an important point for public health interventions. Particular attention to health is warranted for individuals incarcerated in and released from high-security prisons. The potential impact of both individual-level characteristics of people incarcerated in high-security facilities, and of the prison environment itself, on mortality outcomes, should be investigated further.

Funding: The South-Eastern Norway Regional Health Authority and The Norwegian Research Council.