Injection Drug Use and Hiv Infection

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Injection drug use (IDU) contributes to considerable illness burden in both developed and developing countries. Transmission of blood-borne pathogens (e.g., HIV, hepatitis B and C virus, Human T-Cell Lymphotrophic viruses I and II, and malaria) occurs primarily through direct sharing of needles or multi-person use of syringes. More recent studies suggest potential additional risks posed by shared use of injection paraphernalia (e.g., cookers, cotton, water), which is especially a concern with respect to transmission of hepatitis B and C viruses.

Human immunodeficency virus/acquired immunodeficiency syndrome (HIV/AIDS) and injection drug use can be considered as two intertwining epidemics. Socioeconomic, legal, and cultural factors and migration contribute to the emergence of drug injection. Injection drug use has been reported in 144 countries worldwide, among which 128 have detected HIV among injection drug users (IDUs). Although IDUs presently account for 5 to 10 percent of cumulative adult HIV infections worldwide, injection drug use is the predominant mode of HIV transmission in most of Western and Eastern Europe, North Africa, the Middle East, and increasingly in parts of Asia. Taking into account direct transmission among IDUs through sharing of contaminated injection equipment, and indirect transmission to sexual partners and offspring, injection drug use accounts for 44 percent of reported AIDS cases in Europe and nearly one-third of cases in the United States and the Southern Cone of South America. In the United States, approximately half of all new HIV infections are among IDUs. In Canada, the proportion of AIDS cases attributable to injection drug use is steadily increasing.

IDU-associated HIV epidemics are characterized by a high degree of regional and local heterogeneity. Explosive epidemics have occurred in both developing and developed countries or regions, with documented HIV incidence rates reaching as high as 20 to 30 percent per year. Early examples of HIV epidemics among IDUs were documented in Manipur, India Milan, Italy, Bangkok, Thailand, and New York City, suggesting that once HIV prevalence reaches a threshold of approximately 10 percent, it can surpass 40 to 50 percent within one to four years. More recently, Vancouver, Canada, witnessed an HIV outbreak with incidence reaching 18.6 per 100 person-years, despite an extended period of low stable HIV prevalence and a high-volume needle exchange program. In the Ukraine, over 100,000 HIV infections occurred in a single year, mostly due to sharing of injection equipment. These examples serve to illustrate the extent to which IDU-associated HIV epidemics can occur with startling speed. In such cases, subsequent spread to heterosexual non-IDU populations is almost imminent, which underscores the need for swift prevention measures.

In contrast, Australia and the United Kingdom have essentially averted widespread transmission of HIV among drug users. These prevention successes did not occur by chance. The early introduction of interventions such as widespread legal access to sterile injection equipment and expansion of methadone maintenance treatment programs likely spared these regions from the tragedies described above. Preventive strategies to curtail HIV transmission among IDUs are discussed in more detail below.


Several interventions have been developed to reduce the spread of blood-borne disease among IDUs. These include programs that promote sterile syringe acquisition, drug abuse treatment, network-oriented interventions, and community outreach. These programs are briefly summarized.

Since sterile syringes are not accessible, affordable, or legal in the majority of countries that report injection drug use, the fundamental mechanism for reducing parenteral HIV transmission among IDUs is to provide unrestricted access to sterile syringes and to promote their one-time use. Examples are syringe exchange programs (SEPs), syringe vending machines, and enabling IDUs' access to syringes through pharmacies. These interventions are consistent with the concept of harm reduction, which aims to reduce the negative consequences associated with injection drug use among persons who cannot or will not cease injecting, and their surrounding community. At SEPs, IDUs exchange sterile syringes for potentially contaminated ones. A large body of international literature suggests that SEPs can be effective in reducing the incidence of HIV, Hepatitis B, and Hepatitis C, as well as needle sharing. No evidence exists to suggest that SEPs increase drug use or crime. At many SEPs, IDUs can receive condoms, referrals to HIV testing and drug treatment programs, and screening for STDs and tuberculosis. Unfortunately, in many U.S. states where SEPs operate illegally due to syringe paraphernalia laws, these critical ancillary services are less likely to be offered. In many developing countries, even when SEPs have been successfully introduced, severe fiscal restraints limit their ability to consistently offer services to a large number of IDUs.

Drug abuse treatment, and methadone maintenance in particular, has been associated with reduced injection frequency as well as declines in needle sharing, sexual risk behaviors, and HIV seroconversion. These studies support the notion that drug abuse treatment can be effective as primary HIV/AIDS prevention. Other opiate agonist therapies that are undergoing evaluation include substitution with buprenorphine, naltrexone and levo-alpha acetylmethadol (LAAM). Clinical trials have also evaluated the prescription of heroin under continuous medical surveillance, for example, in Switzerland. However, in cities where cocaine and methamphetamine are the main drugs of abuse, little is available in terms of drug abuse treatment. In North America, less that 25 percent of IDUs are receiving drug treatment at any given time, which signals an urgent need for expanded drug treatment services, including but not restricted to methadone maintenance. Other treatmentoriented initiatives that require expansion and evaluation include programs to prevent relapse from abstinence, interim treatment of drug users on waiting lists, interventions to refer SEP attenders into treatment, and development of substitution therapies for drug users addicted to stimulants.

Network and community-level strategies that modify social norms surrounding needle sharing constitute also valuable prevention tools. Network-based strategies of HIV prevention are based upon the personal networks of IDUs. Personal networks include people an IDU may have a social relationship with: an injecting partner, a sex partner, a family member, and so on. Studies have shown that personal network-based interventions can decrease needle sharing, decrease use of shooting galleries, and increase bleach disinfection.

Community-based outreach is characterized by utilization of former IDUs and/or peers to create a liaison between the drug using community and HIV education/treatment. In the United States, outreach has been shown to impact HIV risk by decreasing the frequency of drug use and reuse of needles and increasing use of bleach for purposes of disinfection. M. S. Kumar and colleagues have shown that community-based out-reach may also be effective in an international setting. They demonstrated significant decreases in needle use frequency and needle sharing among IDUs involved in outreached efforts as compared to IDUs not involved in outreach efforts in Madras, India. D. C. Des Jarlais has shown that community outreach is a crucial component held in common by five cities that have consistently maintained low stable HIV prevalence rates among IDU populations.


In several cities that experienced early HIV epidemics among IDUs (e.g., Milan, Italy; Geneva, Switzerland; Amsterdam, the Netherlands; and New York City), HIV prevalence has declined. This has been attributed to AIDS-related mortality, pre-AIDS mortality, improvements in HIV treatments, migration, diminishing size of some IDU populations (e.g., Amsterdam), and reduced HIV incidence as a probable consequence of combinations of the above interventions. However, in the presence of high background HIV prevalence, even low levels of needle sharing can give rise to a relatively high number of new infections. In Amsterdam, large declines in injection risk (i.e., syringe borrowing, lending, and reusing) occurred from 1986 to 1991, and annual HIV incidence declined from 8 percent to 4 percent. However, van Ameijden and colleagues reported no further reductions occurred thereafter, suggesting that a minimum level of injecting risk may persist that is difficult to prevent. Since risk reduction rather than risk elimination appears to be a realistic goal, studies are needed to determine minimum levels of acceptable injection risk for specific regions, based on a thorough understanding of local risk behaviors, HIV prevalence and incidence, mixing patterns of susceptibles, and the estimated impact of interventions. This will require collaboration across the disciplines of epidemiology, behavioral science, and biostatistics.

Apart from the aforementioned strategies of HIV prevention among IDUs, a core prevention strategy that has yet to receive adequate attention is interventions that discourage transition from noninjection to injection drug use. The rationale for this approach is that the prevalence of hepatitis B and C surpasses 50 percent among new initiates to injection drug use within one year after initiation.

There is also evidence to suggest that risk factors for HIV seroconversion among IDUs may differ significantly by gender. For example, among male IDUs, injection-related risks and homosexual/bisexual activity appear to play a predominant role, whereas among females, sexual risks are paramount. These findings suggest that prevention programs should be gender-specific as well as being ethnoculturally and locally sensitive. Future studies should pay special attention to patterns of sexual behaviors of drug users in an effort to develop practical interventions.

In summary, the characteristics of IDU-associated HIV epidemics and interventions that have been effective in reducing IDUs' risk behaviors include access to sterile injecting equipment, methadone maintenance treatment, communitybased outreach, and peer network interventions. Unfortunately, in many settings the implementation of these proven interventions is often delayed due to lack of political will or inadequate resources. The delicate balance between an epidemic that is averted and one that is merely delayed argues against complacency in the realm of prevention. These obstacles will need to be over-come if HIV epidemics among drug user populations are to be controlled or prevented.

Steffanie A. Strathdee

Francisco Inacio Bastos

(see also: Addiction and Habituation; Cocaine and Crack Cocaine; HIV/AIDS; Lifestyle )


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