Can non-injecting drug use protect against blood borne viruses among people who inject drugs? Evidence from Tallinn, Estonia and New York City, USA

Objectives: Many injecting drug users (IDUs) also use drugs through means other than injecting (smoking, snorting, oral). If the non-injecting use substitutes for injecting use, then non-injecting use might protect against infection with blood-borne viruses (BBVs). Methods: In New York City (NYC), 726 IDUs were recruited at a short-term drug detoxification program from 2005-2010. In Tallinn, respondent driven sampling was used to recruit 350 IDUs for a cross-sectional survey in 2007. In both sites, a structured interview was administered and serum samples were collected. Four focus groups were conducted in Tallinn to explore reasons for non-injecting use. Results: In New York, HCV prevalence was 71% among 726 subjects. In a multiple logistic regression analysis, HCV seropositivity was negatively associated with recent intranasal use of heroin (AOR = 0.52, 95% CI 0.33–0.82) and recent intranasal use of speedball (AOR = 0.41, 95% CI 0.21-0.80). HIV prevalence was 16% and associated with sexual risk but not injecting risk. In Tallinn, HIV prevalence was 59% among 350 subjects. In multivariate analysis, recent non-injecting use of drugs other than alcohol was negatively associated with HIV seropositivity (AOR 0.49; 95%CI 0.25-0.97). HCV testing was not conducted. Focus group members specifically mentioned non-injecting use when clean injection equipment was not available. Conclusions: In two different epidemiologic situations, self reported non-injecting drug use was strongly associated with a lower probability of infection with a BBV. Encouraging intranasal use as an alternative to injection among current IDUs may be a viable strategy for reducing transmission of BBVs.