Anna Palmer1, Peter Higgs1,2, Nick Scott1,3, Paul Agius1,3, Lisa Maher1,4, Paul Dietze1,3. 1. Behaviours and Health Risks Program, Burnet Institute, 85 Commercial Rd, Melbourne, VIC, 3004, Australia. 2. Department of Public Health, La Trobe University, Plenty Rd &, Kingsbury Dr, Bundoora, VIC, 3086, Australia. 3. Department of Epidemiology and Preventive Medicine, Monash University, 553 St Kilda Rd, Melbourne, VIC, 3004, Australia. 4. Kirby Institute for Infection and Immunity, UNSW Sydney, Level 6, Wallace Wurth Building, High Street, Kensington, NSW, 2052, Australia.
Abstract
AIMS: To estimate the prevalence of and risk factors associated with concurrent injection of multiple substances (co-injection) among a community-recruited cohort of people who inject drugs. DESIGN: Cross-sectional study. SETTING: Melbourne, Australia. PARTICIPANTS: A sample of 720 actively injecting participants from the Melbourne Injecting Drug User Cohort Study (33% female) was extracted. MEASUREMENTS: We constructed two statistical models: a logistic regression model analysing correlates of co-injection of any substance combination in the past month and a multinomial logistic regression model analysing correlates of three mutually exclusive groups: heroin-diphenhydramine co-injection only, co-injection of other substances and no co-injection. Risk factors examined included drug use characteristics, demographic characteristics, health service use, hepatitis C status, injection risk behaviours and previous experience of non-fatal overdose. FINDINGS: One-third [n = 226, 31%; 95% confidence interval (CI): 28-34%] of participants reported co-injecting substances within the past month, with equal numbers of participants reporting injecting combinations of heroin-diphenhydramine (n = 121, 54%; 95% CI = 48-60%) and heroin-methamphetamine (n = 121, 54%; 95% CI = 48-60%). In logistic regression analyses, reporting co-injection of any substance combination was associated with male sex [adjusted odds ratio (aOR) = 1.80, 95% CI = 1.18-2.74, P = 0.006] and injecting daily or more frequently (aOR = 2.04, 95% CI = 1.31-3.18, P = 0.002). In multinomial logistic regression analyses, participants reporting heroin-diphenhydramine co-injection only were significantly more likely to report groin injecting [adjusted relative risk ratio (aRRR) = 6.16, 95% CI = 2.80-13.56, P < 0.001] and overdose (requiring an ambulance) in the past 12 months (aRRR = 2.81, 95% CI = 1.17-6.72, P = 0.021) compared with participants reporting no co-injection or co-injection of other substances. CONCLUSIONS: A substantial proportion of people who inject drugs report co-injection of multiple substances, which is associated with a range of socio-demographic, drug use and health service use risk factors.
AIMS: To estimate the prevalence of and risk factors associated with concurrent injection of multiple substances (co-injection) among a community-recruited cohort of people who inject drugs. DESIGN: Cross-sectional study. SETTING: Melbourne, Australia. PARTICIPANTS: A sample of 720 actively injecting participants from the Melbourne Injecting Drug User Cohort Study (33% female) was extracted. MEASUREMENTS: We constructed two statistical models: a logistic regression model analysing correlates of co-injection of any substance combination in the past month and a multinomial logistic regression model analysing correlates of three mutually exclusive groups: heroin-diphenhydramine co-injection only, co-injection of other substances and no co-injection. Risk factors examined included drug use characteristics, demographic characteristics, health service use, hepatitis C status, injection risk behaviours and previous experience of non-fatal overdose. FINDINGS: One-third [n = 226, 31%; 95% confidence interval (CI): 28-34%] of participants reported co-injecting substances within the past month, with equal numbers of participants reporting injecting combinations of heroin-diphenhydramine (n = 121, 54%; 95% CI = 48-60%) and heroin-methamphetamine (n = 121, 54%; 95% CI = 48-60%). In logistic regression analyses, reporting co-injection of any substance combination was associated with male sex [adjusted odds ratio (aOR) = 1.80, 95% CI = 1.18-2.74, P = 0.006] and injecting daily or more frequently (aOR = 2.04, 95% CI = 1.31-3.18, P = 0.002). In multinomial logistic regression analyses, participants reporting heroin-diphenhydramine co-injection only were significantly more likely to report groin injecting [adjusted relative risk ratio (aRRR) = 6.16, 95% CI = 2.80-13.56, P < 0.001] and overdose (requiring an ambulance) in the past 12 months (aRRR = 2.81, 95% CI = 1.17-6.72, P = 0.021) compared with participants reporting no co-injection or co-injection of other substances. CONCLUSIONS: A substantial proportion of people who inject drugs report co-injection of multiple substances, which is associated with a range of socio-demographic, drug use and health service use risk factors.