Viewpoint

Should we conclude from these differences that our current approaches to prevention of bloodborne viruses among IDUs (which are based on the harm-reduction philosophy and include needle and syringe distribution, methadone maintenance therapy, peer education and advocacy) are ineffective? This is unlikely for two reasons. Firstly, HIV has a very low incidence in Australian IDUs, but continues to spread rapidly among IDUs in many parts of the United States and in other populations lacking equally comprehensive prevention strategies. Secondly, there have been dramatic declines in transmission of other viruses (hepatitis B and D) among Australian IDUs since the mid 1980s.¹ The effectiveness of just one element of our harm reduction programs -- needle and syringe exchange -- has been well demonstrated,³ and is supported by an American study which found that IDUs in needle exchange programs were seven times less likely to be exposed to HCV than those who were not.⁴

Can the difference be explained by HCV spreading in a different manner to HIV? Sexual transmission of HCV is rare⁵ and is unimportant epidemiologically, while the reverse applies for HIV. Both viruses are transmitted between IDUs by blood contact. The determinants of the epidemics are background virus prevalence, virus infectiousness and the existence of behaviour that permits spread. Sharing needles and syringes is generally acknowledged as the most important means of spread between IDUs, and has consistently been found to be the major association with HCV transmission among IDUs worldwide. Since the early 1980s, in response to the threat of HIV infection, there have been substantial declines in needle-sharing among Australian IDUs. About 13% of IDUs in Melbourne reported having shared a needle and syringe in the preceding month in 1994, compared with 38% in 1989.⁶ Nevertheless, it remains a problem, and higher proportions of IDUs who share needles and syringes are found among substantial minority groups, such as Vietnamese migrants and prisoners.^6,7

There is emerging evidence of the importance of blood contact between IDUs in ways other than sharing needles and syringes. Videotapes of groups of IDUs reveal many opportunities for exposure to viruses through blood contaminating equipment other than needles and syringes. This includes swabs, spoons, water vials and tourniquets, as well as fingers, other body parts and surfaces in the immediate environment.¹ For example, a user applying a tourniquet to a partner's arm might deposit a tiny smear of blood on skin which is subsequently punctured by a needle, or wipe blood from an injection site and let the swab fall onto a communal tabletop. The risk associated with such behaviour is greater for HCV than for HIV, because the higher infectiousness of HCV⁸ means smaller amounts of blood can efficiently transmit the infection. Two studies have attempted to quantify IDUs' risk of HCV transmission in the absence of needle-sharing: one found an incidence of about 4% per year among those who reported never sharing needles and syringes, compared with about 17% per year among those who did;⁹ the second, 11.9% compared with 30.2%.¹⁰ Both studies potentially suffered from misclassification bias, with some of those reporting never sharing actually having shared. Such bias would exacerbate the difference between the two incidences, further supporting the conclusion that the majority of HCV infections among Australian IDUs are associated with needle-sharing.

Risky behaviour permits the blood contact necessary for both HCV and HIV transmission, and the higher infectiousness of HCV undoubtedly explains some of the difference in incidence. Background viral prevalence is the other critical factor. HCV prevalence is now so high that even very occasional sharing of needles and syringes carries an extreme risk of HCV infection, to which must be added the unknown but non-negligible risk due to "environmental" contamination. With a low-prevalence virus such as HIV, high-risk behaviour must be far more frequent and prevalent in a population before the risks of transmission become large enough to sustain continued spread. Given the much higher infectiousness of HCV per contact episode and its much higher prevalence in Australian IDUs relative to HIV, the difference in incidence comes down to the force of numbers. The Table combines background prevalences of HCV and HIV, estimates of infectiousness, and carrier rates to illustrate the difference in infection risk encountered by IDUs in Australia. On the basis of these crude estimates, an IDU sharing a needle used by another IDU of unknown infection status is at somewhere between 150 and 800 times higher risk of infection with HCV than HIV.

Despite this somewhat sobering picture, it should be noted that there are tentative indications that HCV incidence in Australian IDUs has been declining in recent years. Modelling has suggested that incidence may have fallen from around 18% per year before 1987 to around 12% per year thereafter;¹ a Victorian cohort study found a decline from 16.6 cases per 100 person-years in 1990-91 to 8.1 per 100 person-years in 1994-95, matched by declines in behavioural risk;⁹ and HCV prevalence among IDUs tested for the first time at a methadone maintenance program in Melbourne decreased from 75% in 1992 to 50% in 1995.¹²

The conclusion from all these considerations is that control of the HCV epidemic requires more intense concentration on reducing needle-sharing and other risky behaviour, and will require a greater effort to decrease incidence than HIV has. This has been seen with HIV infection among IDUs in other countries -- epidemics which have reached high prevalences have proven much harder to control than epidemics which have not taken off before interventions began. Further decreases in needle-sharing will require increased support for accepted programs (increased funding and reach of needle exchange programs, pharmacy sales, peer education) as well as consideration of new strategies. These should urgently include needle exchange programs in prisons (where needle-sharing is the norm)¹³ and youth training centres, safe injecting spaces, special programs for Aboriginal IDUs and people of non-English-speaking background, and deregulation of supply of needles and syringes so they can be purchased from outlets such as service stations and convenience stores.

Other strategies, such as promoting transition to the smoking rather than injecting of illicit drugs, are worth further research and consideration. Finally, the importance of hygiene with regard to injecting environments and conditions must be strongly and routinely stressed. Without serious commitment to new and expanded strategies -- especially needle exchange -- the HCV epidemic will continue, with its high and growing toll of illness and cost.

1. Crofts N, Jolley D, Kaldor J, et al. The epidemiology of HCV infection among injecting drug users in Australia. J Epidemiol Community Health 1997; 51: 692-697.
2. National Centre in HIV Epidemiology and Clinical Research. HIV/AIDS and related diseases in Australia: annual surveillance report, 1998. Sydney: National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, 1998.
3. Hurley SF, Jolley DJ, Kaldor JM. Effectiveness of needle-exchange programs for prevention of HIV infection. Lancet 1997; 349: 1797-1800.
4. Hagan H, Des Jarlais DC, Friedman SR, et al. Reduced risk of hepatitis B and hepatitis C among injection drug users in the Tacoma Syringe Exchange Program. Am J Public Health 1995; 85: 1531-1536.
5. Wyld R, Robertson JR, Brettle RP, et al. Absence of hepatitis C virus transmission but frequent transmission of HIV-1 from sexual contact with doubly-infected individuals. J Infect 1997; 35:163-166.
6. Crofts N, Webb-Pullman J, Dolan K. An analysis of trends over time in social and behavioural factors related to the transmission of HIV among injecting drug users and prison inmates. Canberra: AGPS, 1996.
7. Louie RL, Krouskos D, Gonzalez M, Crofts N. Vietnamese-speaking injecting drug users in Melbourne: the need for harm reduction programs. Aust N Z J Public Health 1998; 22: 481-484.
8. Patz JA, Jodrey D. Occupational health in surgery: risks extend beyond the operating room. Aust N Z J Surg 1995; 65: 627-629.
9. Crofts N, Aitken CK. Incidence of bloodborne virus infection and risk behaviours in a cohort of injecting drug users in Victoria, 1990-1995. Med J Aust 1997; 167: 17-20.
10. van Beek I, Dwyer R, Dore GJ, et al. Infection with HIV and hepatitis C among injecting drug users in a prevention setting: retrospective cohort study. BMJ 1998; 317: 433-437.
11. MacDonald M, Wodak AD, Ali R, et al. HIV prevalence and risk behaviour in needle exchange attenders: a national study. The Collaboration of Australian Needle Exchanges. Med J Aust 1997; 166: 237-240.
12. Crofts N, Nigro L, Oman K, et al. Methadone maintenance and hepatitis C virus infection among injecting drug users. Addiction 1997; 92: 999-1005.
13. Crofts N, Thompson S, Wale E, Hernberger F. Risk behaviours for blood-borne viruses in a Victorian prison. Aust N Z J Criminol 1996; 29: 20-28.

National Centre in HIV Epidemiology and Clinical Research, Darlinghurst, NSW.
John M Kaldor, PhD, Deputy Director.

Reprints will not be available from the authors.
Correspondence: Dr N Crofts, Centre for Harm Reduction, Macfarlane Burnet Centre for Medical Research, PO Box 254, Fairfield, VIC 3078.
Email: croftsATburnet.edu.au

Journalists are welcome to write news stories based on what they read here, but should acknowledge their source as "an article published on the Internet by The Medical Journal of Australia <http://www.mja.com.au>".
<URL: http://www.mja.com.au/>