Mortality of those who attended drug services in Scotland 1996–2006: Record-linkage study

BACKGROUND: We examine major causes of death amongst persons in contact with drug-treatment services across Scotland during April 1996-March 2006, hereafter Scottish Drug Misuse Database (SDMD) cohort. METHODS: Drug-treatment records were linked to national registers of deaths and hepatitis C virus (HCV) diagnoses. For eras 1996/97-2000/01 and 2001/02-2005/06, we calculated cause-specific death-rates and standardised mortality ratios (SMRs) using age-, sex- and calendar-rates of the general Scottish population. Major causes of death were identified by high SMRs (>5 across eras) or rates (>50 per 100,000 person-years in either era), and their time-specific influences characterised by proportional hazards analyses. RESULTS: The SDMD cohort comprised 69,456 individuals, 350,315 person-years and 2590 deaths. The overall SMR reduced from 6.4 (95% CI: 6.0-6.9) to 4.8 (95% CI: 4.6-5.0) between eras. We identified five major causes of death: drug-related (1383 deaths), homicide (118) and infectious diseases (90) with high SMRs; suicide (269) and digestive system disease (168) with high rates. HCV diagnosis marked individuals with at least double the risk of cause-specific mortality, including adjusted hazard ratio (HR) for no HCV diagnosis of 0.46 (95% CI: 0.41-0.53) for drug-related deaths (DRDs) and 0.15 (95% CI: 0.10-0.22) for death from digestive system disease. Increased DRD risk at older age (>34 years) appeared specific to HCV-diagnosed individuals (interaction: χ₁²=7.7, p=0.01). Alcohol misuse increased HRs: for DRD (1.76, 95% CI: 1.50-2.06), suicide (1.88, 95% CI: 1.35-2.60), deaths from digestive system disease (3.19, 95% CI: 2.21-4.60) and non-major causes (1.87, 95% CI: 1.49-2.35). Stimulant misuse increased suicide risk: adjusted HR 1.91 (95% CI: 1.43-2.54). CONCLUSIONS: Drug-users in Scotland are exposed to variously increased mortality risks. HCV-diagnosed individuals are particularly vulnerable, and may need additional support.