Characteristics of polydrug use and associations with HIV risk behaviours among people who inject drugs in two cities in Europe

Background - Non-medical drug injection is a major risk factor for HIV infection in Estonia and Russia. The use of multiple drugs (polydrug) among injectors has also been associated with increased harms. We compared HIV, hepatitis C, injecting and sexual risk associated with different drug combinations among people who injected drugs (PWID) in 2012-2013 in Kohtla-Järve (Estonia, n=591) and St Petersburg (Russia, n=811).

Methods – Using latent class analysis, we identified five drug use classes within the sample of drug users. The largest class consisted of single-drug injectors among whom an opioid was the sole drug injected (56% of PWID). The four polydrug classes included polydrug-polyroute injectors who injected and used opiates and stimulants (9%), opiate-stimulant poly-injectors who injected amphetamine-type-stimulants with a primary opiate (7%) and opiate-opioid poly-injectors who injected opioids and opiates (16%). Non-injection stimulant co-users were injectors who also used (but did not inject) non-injection stimulants (12%).

Results - All four polydrug classes were associated with greater injection risks than single-drug injection in multivariable regression, while opiate-stimulant and opiate-opioid poly-injection were also associated with having multiple sex partners. Riskier injection and sexual behaviours among polydrug injectors suggest increased potential for the transmission of blood-borne and sexually transmitted infections.

Conclusions – Characterizing polydrug use as drug combinations highlighted consistently higher risk behaviours among polydrug injectors and important differences among them in injecting and sexual risk-taking. Generic drug class combinations could help programmes better understand and address class-specific behavioural and infection risks associated with different practices in drug-using populations. Harm reduction services tailored to specific demographic and risk profiles must factor in drug-appropriate treatment and sexual risk reduction strategies to curb sexual and parenteral transmission of infections.