HCV is an infectious blood-borne virus first identified in 1989. According to the US Centres for Disease Control and Prevention (CDC), it is the most common chronic bloodborne infection in the United States17. While 15% to 25% of persons with HCV resolve their infection, the remaining 75% to 85% of cases go onto chronic infection1,4. Most newly infected persons (60% to 70%) have no symptoms and are unaware of their infection, but are infectious and may spread the virus through high-risk behaviours4.
Long term consequences of HCV infection include cirrhosis, hepatocellular carcinoma and other extra-hepatic manifestations4,5,18,19. HCV is responsible for 40% of chronic liver disease, and HCV-associated end-stage liver disease is the most frequent indication for liver transplantation among adults6,20. HCV-related chronic liver disease causes 8,000 to 10,000 deaths each year in the United States6,21 and 800 to 1,000 deaths per year in Canada19.
While the estimated population prevalence rates are low - approximately 0.8% in Canada1,3,22 and 1.8% in the United States6,21 - they increase dramatically among high-risk groups such injection drug users23,24, incarcerated populations25,26 and street youth1,27.
In some cases, HCV can be effectively treated. However, current treatments are only indicated for 20% to 30% of the infected population20,28. Treatment is effective in 40% to 80% of these cases29, with success dependent on genotype, type of treatment, length of treatment and stage of disease30,31. There is no vaccine for HCV, and re-infection is possible4. This means that prevention relies primarily on the successful interruption of viral transmission and on modification of high-risk behaviours.
As many people have multiple risk factors, establishing the exact mode of transmission is often difficult. In the absence of clear risk factors such as IDU, determining which factors - many of which will be forgotten or denied - resulted in transmission is extremely challenging.
In IDU populations, the high HCV prevalence, the high rate of chronic infection, the steady influx of new, susceptible injecting users and the high transmissibility of the virus all contribute to its endemicity12,15.
There are an estimated 125,000 people who use injection drugs in Canada32 and approximately 1.5 million in the United States33. The estimated average HCV prevalence in these populations is 80%15, reaching a high of 90% or more in several communities, including in Vancouver, British Columbia12,23,24. Worldwide, estimates of HCV prevalence in IDU populations range from 50% to 100%4,23,24. IDU accounts for at least 60% of all annual HCV infections in the United States and Canada2,6,15,16.
When injecting drugs, individuals use - and often share - many different pieces of equipment, including needlesa, cookers, swabs, cotton/filters, tourniquets and water. Sharing any of this equipment is a major risk factor for infection2,34. Thorpe et al. reported that sharing cookers is the most significant predictor of HCV infection after controlling for needle sharing, with an adjusted relative hazardb (RH) of 4.07. Sharing cotton filters and/or rinse water were also significant predictors of infection in some situations (RH=2.4 & 2.7, respectively)34.
Health Canada's Enhanced Surveillance System for HBV and HCV revealed that, in the period 1998-1999, 78% of injection drug users interviewed reported having shared needles in the six months before diagnosis1,15. The Vancouver Injecting Drug Use Study (VIDUS) found that of participating individuals who had injected drugs in the six months prior to questionnaire completion, 28% reported sharing needles in that time35. Likewise, a 1995-1997 New Mexico study found that 90% of participating injection drug users reported sharing injection equipment, primarily with friends (52%) or with their main sex partner (31%). Of those who reported sharing equipment, 85% were anti-HCV positive36. Many of these people are unaware of their HCV infection and engage in more at-risk behaviours than those who are aware of their positive status37.
Equipment sharing is of particular concern among young adults who are newly indoctrinated into the drug culture. A Chicago study found that almost three quarters (74%) of young adult injection drug users - half of whom had just started injecting during the two years prior to enrolment in the study - had shared injection equipment within the previous six months34.
Specific drugs increase the risk of HCV infection. Cocaine use, which often involves up to 20 injections per day, increases the likelihood that drug equipment will be shared4. Cocaine is also often inhaled and causes nasal erosions and ulcers, creating the potential for HCV to be transmitted through the sharing of cocaine straws4,6. Dry and cracked lips, a common side effect of injection drug use, make pipe sharing a potential risk4,6. Certain injection practices also increase risk. For example, 'front loading' or 'back loading' where drugs are mixed in one syringe and distributed to other syringes, passes potentially infected materials to several people at one time4.
Injection drug use and equipment sharing has also made HCV a significant problem in incarcerated populations. Anti-HCV positive rates among inmates in Canada range from 28% to 40%25,26. While many infections occur outside of prison, transmission has also been documented while in custody, with infection likely a result of IDU38.
In the past, a significant number of HCV infections were due to infected blood products2,13, although in the last decade universal blood donor screening has reduced this risk to approximately 1 in 500,000 donations39.
HCV can also be transmitted during pregnancy and childbirth9,10 and through needle-stick injury6,7, sexual contact6-8, tattooing, body piercing, electrolysis11,12 and sharing of personal hygiene items such as toothbrushes and razors that may be contaminated with blood1,12. These modes of transmission, however, account for a very small number of acute HCV infections compared with IDU1,6,13,14.
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