Sharing injecting equipment is associated with a low per-event probability of hepatitis C virus (HCV) transmission, Australian investigators report in the online journal PLOS ONE. Their analysis also showed that sharing injecting equipment with someone with hepatitis C had a transmission probability of up to 6%, depending on factors such as cleaning of equipment and HCV viral load. Because the per-event probability was so low, the investigators believe that HCV prevention campaigns should focus on reducing the frequency of sharing equipment, as well as focusing on decreasing the per-event risk.
“This analysis suggests that an important strategy to reduce HCV transmission would be to reduce the number of sharing events, in addition to employing strategies aimed at reducing the per-event risk (e.g., by bleaching),” write the researchers. “This may be accomplished by implementing needle/syringe exchange programs, intensive rehabilitation, bleach and other decontamination strategies, or by increasing coverage of opioid substitution programs.”
HCV is a blood-borne infection. The majority of infections in resource-rich settings are associated with the sharing and/or reuse of injecting equipment by people who inject drugs.
The per-event probability of HCV infection following an episode of sharing is uncertain. Factors such as background HCV prevalence rates, the cleaning of equipment and the HCV viral load of the person with HCV with whom equipment is shared can all impact on the per-event risk.
A more precise knowledge of the per-event risk could help shape HCV prevention messages and strategies. Investigators in New South Wales, Australia, therefore designed a study involving people in prison who inject drugs. Participants in the study were tested for HCV every six months and asked about their injection risk behaviours, including the sharing and/or reuse of needles, syringes and other injecting paraphernalia. Taking into account HCV incident rates and self-reported risk behaviours, the researchers estimated the per-event probability of HCV infection after sharing equipment and the transmission probability when sharing with a person with HCV.
The study was conducted between 2005 and 2012.
A total of 92 individuals were recruited. Most (70%) were male and their median age was 25 years. The median duration of injecting drug use was six years.
Overall, participants reported a median of 148 injecting episodes per year, and a median of 27 injecting episodes involving the sharing of equipment.
During two years of follow-up, 37 individuals (40%) acquired HCV. All these individuals reported sharing. Comparison with inmates who remained HCV-uninfected showed that those who contracted HCV reported more episodes of injecting (p < 0.01) and also more episodes of sharing injecting equipment (p < 0.05).
The authors estimated that the per-event probability of HCV infection after sharing injecting equipment was 0.57% (CI: 0.32%-1.05%).
But the actual per-event risk could be much lower. If the actual incidence of sharing equipment was higher, even 100%, then the per-event probability was just 0.17%.
A retrospective analysis of 75 men who injected drugs yielded a per-event probability of 0.42%.
In a series of sensitivity analyses, the per-event probability was between 0.26%-0.72% (CI: 0.11%-3.8%).
The transmission probability after sharing injecting equipment with a person with HCV was as high as 6%.
“This analysis provides, to our best knowledge, the first quantitative estimates of the per-event probability of HCV infection following an IDU event with sharing of injecting equipment,” write the investigators. “Comparable studies are warranted in community-based cohorts…these transmission estimates will inform planning and evaluation of prevention strategies for the HCV epidemic in both the community and custodial settings.”
Boelen L et al. Per-event probability of hepatitis C infection during sharing of injecting equipment. PLOS ONE 9(7): e100749. doi: 10.1371/journal.pone.0100749 (2014).