RISK-FACTORS FOR OVERDOSE MORTALITY - A CASE-CONTROL STUDY WITHIN A COHORT OF INTRAVENOUS-DRUG-USERS

Overdose mortality is the major adverse health effect of drug injectio n. The potential determinants of overdose death are poorly understood; the aim of this study was to investigate risk factors for overdose mo rtality among intravenous drug users (IVDU). A cohort of 4200 IVDU att ending methadone treatment centres in Rome during the period 1980-1988 , was enrolled. Data were collected from clinical records. Vital statu s and cause of death were ascertained as of 31 December 1988. A matche d case-control analysis within the cohort was performed to identify ri sk factors of death from overdose. All overdose deaths were included a s cases and four controls, matched on year of birth and sex, were sele cted for each case from among the cohort members still alive at the ti me of death of the corresponding case. In all, 81 deaths from overdose were identified as cases and compared with 324 controls. A high risk of overdose death occurred among subjects who left treatment compared with those still in treatment (odds ratio [OR] = 3.55, 95% confidence interval [Cl] : 1.82-6.90). The OR was particularly elevated in the fi rst 12 months after drop-out compared with those retained in treatment (OR = 7.98, 95% Cl : 3.40-18.73). The risk of overdose death was high er for unmarried compared with married people (OR = 2.48, 95% Cl : 1.3 1-4.68); a higher risk of overdose death was also associated with lowe r educational status and younger age at first drug use, but such assoc iation was not statistically significant. Methods to predict drop-out, in order to increase retention in treatment, and strategies to mainta in contact with dropouts are warranted to decrease overdose mortality.