Evidence-based findings on the efficacy of syringe exchange programs: an analysis of the scientific research completed since April 1998

by David Satcher, MD, Assistant Secretary for Health and Surgeon General


The issues of substance abuse addiction and HIV transmission related to injection drug use remain serious public health challenges, and the need to define and implement effective public health interventions remain urgent. The scientific research continues to define the unique role that syringe exchange programs can play in curtailing the expansion of the HIV epidemic in vulnerable communities affected by substance abuse, as part of a well designed and implemented comprehensive HIV prevention strategy.

This paper provides a review of recently published peer-reviewed research on syringe exchange programs completed by senior scientists and public health experts within the Department of Health and Human Services. An overview of the research studies is followed by an annotated bibliography providing the published abstracts, directly quoted, and relevant commentary. In summary, the new studies contribute substantially to the strength of the data showing the following effects of effective syringe exchange program

  • a decrease in new HIV seroconversions;
  • an increase in the numbers of injection drug users referred to and retained in substance abuse treatment; and
  • well documented opportunities for multiple prevention services and referral and entry into medical care.

The data indicate that the presence of a syringe exchange program does not increase the use of illegal drugs among participants in syringe exchange programs, and in many cases, a decrease in injection frequency has been observed among those attending these programs. (Bold added)

Throughout the literature, the terms syringe exchange programs and needle exchange programs have been used interchangeably in characterizing programs providing sterile injection equipment to injection drug users. This paper will use the term syringe exchange program, except where a published abstract has specified needle exchange program.


Numerous studies have shown that syringe exchange programs reach and serve the most disenfranchised populations at high risk for HIV infection. In this regard, syringe exchange -programs play a unique role in facilitating the engagement of these populations in meaningful prevention interventions and treatment opportunities, when implemented as part of a comprehensive HIV prevention and substance abuse strategy. The scientific evidence accumulated to date provides a basis on which municipalities that are heavily affected by an HIV epidemic driven by injection drug use should consider syringe exchange programs as a tool for the identification, referral and retention of active users of injection drugs into these services, as part of a comprehensive HIV prevention plan.

Serious discussions about syringe exchange programs must be placed in the context of the HIV epidemic in this country. The urgency to address the consequences of substance abuse is clear, as injection drug use continues to fuel the HIV epidemic in the United States. As many as half of new HIV infections are caused by the sharing of injection equipment contaminated with HIV, either directly due to injection drug use, through unprotected sex with someone who acquired HIV infection through injection drug use, or birth to a mother who acquired HIV infection through these means (CDC, 1999). Women of color and their children continue to be disproportionately affected by HIV/AIDS due to injection drug use. An estimated three out of four AIDS cases among women are due to injection drug use or heterosexual contact with someone infected with HIV through injection drug use, and over 75% of new infections in children result from the consequences of injection drug use in a parent (CDC, 1999). All too often women are unaware of their risk, due to a distant history of drug use in a partner. The ability to halt this devastating epidemic, particularly among minority women and children, requires a three part strategy: (I) preventing substance abuse; (ii) facilitating entry of those with addictions into substance abuse treatment; and (iii) establishing effective outreach to engage active and former drug users in HIV prevention strategies that will protect them, their partners and families from exposure to HIV, and bring them into substance abuse treatment and medical care. HIV prevention and treatment programs targeting HIV-infected injection drug users and their partners, and similar programs within criminal justice institutions, are also important components in preventing the transmission of HIV.

In the Department's prior reviews of the literature on syringe exchange programs in 1997 and 1998, there was discussion of the methodological issues and constraints present across most published studies in this area. These include self-reported measures and difficulty in establishing proper control groups. However, the Department's senior scientists continue to concur with the conclusion of the Institute of Medicine that the pattern of evidence is sufficiently strong to support scientifically clear conclusions regarding the utility of syringe exchange programs, in communities that choose to adopt them, as part of a comprehensive HIV prevention strategy.

A recent national survey of syringe exchange programs (Paone et al, 1999) found that a growing number of local communities have chosen to implement a syringe exchange program to reach injecting drug users who are not in substance abuse treatment, in order to reduce the transmission of HIV through reduction in drug use behaviors and unsafe injection practices. This survey also documented that, in addition to exchanging sterile syringes for contaminated ones, 97% of syringe exchange programs provide a range of other services including referral to substance abuse treatment, prevention education for sexually transmitted diseases, HIV counseling and testing, tuberculosis screening, and primary health care. These trends also were found in a 1997 national survey (CDC, 1998).

The biological rationale for removing contaminated injection equipment from circulation has been demonstrated in a new study by Abdala et al (1999), confirming empirical observations of previous studies. This study showed that HIV-1 can survive over 4 weeks in a contaminated syringe, remaining infectious to individuals who reuse that syringe over this prolonged period. Riley et al (1998) found that 10.9% of used syringes discarded in needle boxes at community locations tested positive for the FUV antibody, while Robles et al (1998) reported that 27% of contaminated syringes returned to a new needle exchange program were positive for HIV. The longevity of the HIV-I virus, combined with its prevalence in used equipment in some communities, is basic to the public health rationale for removal of used syringes from the community environment.

Knowledge of the effectiveness of syringe exchange programs in reducing the sharing of injection equipment and reuse of contaminated syringes among injection drug users has recently been reinforced by a number of new studies (Heimer et al, 1998; Robles et al, 1998; Bluthenthal et al, 1998). Conversely, the closing of an established syringe exchange program in Connecticut was associated with an increase in reuse and sharing of contaminated equipment among injection drug users, exposing these individuals and their partners and families to an increased risk of preventable bloodborne diseases (Broadhead et al, 1999).

Recent research studies document the role that effective syringe exchange programs serve as mechanisms to engage very high risk and hard to reach individuals in substance abuse treatment services. Brooner et al (1998) found that half of syringe exchange program clients referred for substance abuse treatment actually entered treatment, with 76% completing the first 13 weeks of treatment. These results were achieved despite the fact that these clients had more severe drug use, more HIV risk behaviors, less employment and greater engagement in illegal activities than, clients referred to substance abuse treatment from traditional sources. Hagan et al (In Press) reported reduced frequency of injection drug use among current and former users of a needle exchange program, and entry into methadone treatment programs among former, current and new users of a syringe exchange program. Strathdee et al showed that attendance at a syringe exchange program was positively associated with individuals entering detoxification services independent of other variables, again representing an important bridge that facilitates entry into substance abuse treatment.

Concerns about elevated HIV seroconversion rates linked to the use of syringe exchange programs remain scientifically unfounded, as the data primarily reflect the impact of multiple high-risk factors among individuals who participate in these programs - a population at extremely high risk that. is not engaged in appropriate interventions through traditional mechanisms of outreach and treatment referral. Studies of HIV incidence among two study cohorts in Canada, and some recent data on the incidence of hepatitis B and hepatitis C in Seattle, are relevant as these relate to syringe exchange programs. In the Department's internal review of these data in 1998, careful attention was given to the study data on these Canadian cohorts, with the conclusion that syringe exchange programs were not associated with an increase in HIV seroconversions: Subsequent data from the Montreal cohort (Bruneau et al, 1999) have confirmed this lack of association between HIV seroconversion and attendance at a syringe exchange program, with longer follow-up of the study participants and appropriate availability of sterile injection supplies. Efforts to identify any grounds for a causal relationship continue to show negative results (Schecter et al, 1999), when controlling for risk factors in the statistical model.

Public health scientists have long known about the incidence of hepatitis B (HBV) and hepatitis C (HCV) among injection drug users. These are highly infectious bloodborne diseases that are endemic among some drug-using populations. In Seattle, where there is a high prevalence of hepatitis C among injection drug users (70%-80%), participation in the syringe exchange program did not appear to be protective against new HCV or HBV infection (Hagan et al, 1999). Because of the high background prevalence of HCV in this population, a single exposure to a syringe used by an injection drug user carries a high level of risk that it will be contaminated with HCV. Although syringe exchange programs can greatly reduce the reuse of contaminated syringes, maximal prevention of HCV transmission among this population would require distribution of a sufficient volume of sterile syringes to preclude any reuse of injecting equipment. In contrast to this scenario, since HIV seroprevalence is yet low in this population, the empirical data support the potential of a protective effect for HIV among individuals seeking clean injection equipment at the syringe exchange program.

In summary, injection drug use is a driving force for new HIV infections, disproportionately affecting minority populations. Yet, HIV transmission via injection drug use is preventable. Efforts to halt the HIV epidemic are in part dependent on effective prevention interventions targeted to this population. Prevention will require successfully engaging injection drug users and bringing them into systems of care that offer substance abuse treatment, mental health, medical, and social support services. The availability of medical, social and preventive services alone are often not enough to engage the highest risk populations of active injection drug users, absent effective methods of outreach to this population. The scientific research has shown that well designed and implemented syringe exchange programs have demonstrated efficacy in engaging populations at severe risk for HIV and reducing the further spread of HIV among injection drug users, their sexual partners and children. Furthermore, these programs have not been shown to encourage the use of illegal drugs, and fit well into comprehensive substance abuse treatment strategies.

After reviewing all of the research to date, the senior scientists of the Department and I have unanimously agreed that there is conclusive scientific evidence that syringe exchange programs, as part of a comprehensive HIV prevention strategy, are an effective public health intervention that reduces the transmission of HIV and does not encourage the use of illegal drugs. In many cases, a decrease in injection frequency has been observed among those attending these programs. In addition, when properly structured, syringe exchange programs provide a unique opportunity for communities to reach out to the active drug injecting population and provide for the referral and retention of individuals in local substance abuse treatment and counseling programs and other important health services. The scientific evidence accumulated to date provides a basis on which municipalities that are heavily affected by an HIV epidemic driven by injection drug use should consider syringe exchange programs as a tool for the identification, referral and retention of active users of injection drugs into these services, as part of a comprehensive HIV prevention plan.