Studying the effectiveness of an HIV prevention program that facilitates sustained risk reduction is extremely difficult. Research ethics require that comparison subjects be provided with some intervention to reduce their chances of HIV infection, and it is not easy to determine an appropriate comparison condition for a program. Should the comparison subjects be told/permitted to purchase sterile injection equipment from pharmacies? Should they be told to purchase sterile injection equipment through an illicit market? or find some method of disinfecting their own injection equipment?
The logical unit of analysis in an exchange evaluation would be the needs of the local population of injecting drug users rather than the needs of individual drug users. If HIV-infected drug users participate in exchanges—returning their needles and syringes to the exchange rather than passing them on to other injectors—those who do not participate in the exchange would then still be protected against HIV infection. Using communities as the unit of analysis in a clinical trial, however, would be extremely expensive, and it is doubtful that many communities would accept random assignment to experimental or control conditions.
No needle-exchange study as of 2000 has approached a randomized clinical trial. Most studies have measured HIV risk behavior prior to and after participation in an exchange, or have compared risk behavior among exchange participants with that of some other group of injecting drug users. Conclusions about the effectiveness of needle-exchange programs must thus be drawn from the consistency of findings across many methodologically limited studies, rather than rely on a single or small group of methodologically rigorous tests of needle exchange. It should be noted, however, that a consensus panel of the National Institutes of
Jason Farrell, Executive Director of the Positive Health Project, shows syringes to Senior Peer Educator Virgilio Cintron at the agency's offices in New York City, March 6, 2000. The project runs 160 syringe exhange programs for drug users in the U.S. (AP Photo/Jeff Geissler)
Health in February 1997 concluded that needle exchange programs in general, ''show reduction in risk behavior as high as 80 percent in [IDUs], with estimates of a 30 percent reduction of HIV'' (Fuller, 1998). In addition, the Centers for Disease Control, the American Medical Association, and the American Public Health Association, have all in some measure acknowledged the amalgam of data pointing toward needle exchange programs as being successful in reducing the incidents of HIV (AIDS Alert, 2000).
Drug Injection. A common concern expressed by opponents to exchange is that the programs would increase the frequency of illicit drug injection. However, research studies have consistently found that such exchange is not associated with any detectable increase in drug use on either a community or an individual level (Des Jaríais & Friedman, 1992). The most recent review emphasized that ''there is no evidence that needle exchange programs increase the amount of drug use by needle exchange clients or change overall community levels of noninjection or injection drug use'' (Lurie & Reingold, 1993). Of the eight relevant studies analyzed in this review, three found reductions in injection associated with needle exchange, four found mixed or no effect, and one found an increase in injection compared with the controls. Data from the New York City exchange evaluation (which were not available at the time of Lurie & Reingold's 1993 review) indicate a modest decrease in the frequency of injection among participants using needle exchange (Paone et al., 1995).
Moreover, although opponents have often expressed an additional concern—that exchange programs would attract new injectors—the overwhelming number of IDUs participating in exchanges have long histories of drug injection. The mean length of time usually ranges from five to ten years or more. Typically only 1 to 2 percent of exchange participants initiated drug injecting within the previous year. If providing sterile injection equipment had induced large numbers of people to begin injecting drugs, then the numerous studies to date should have observed substantial numbers of new injectors participating in programs.
HIV Injection Risk Behavior. Consistent findings across studies indicate declines in self-reported frequencies of injection with potentially HIV-contaminated needles (Paone et al., 1993). The magnitude of the reduction is difficult to estimate, because studies have used different metrics for risk behavior; some studies have used differences in pre- and post-exchange measurements, while other studies have compared participants with various other groups of drug injectors. Nonetheless, the trend observed from participants in a program has been a reduction in risk behavior, through injection of contaminated equipment, ranging from 50 percent to 80 percent. No studies, however, have shown anything approaching complete elimination of risk behavior among needle-exchange participants.
Exchange programs probably attract drug injectors who are relatively concerned about their health, and it is possible that, even in the absence of exchange programs, these injectors would seek alternative ways of reducing HIV injection risk, such as purchasing sterile injection equipment from pharmacies or on the illicit market. Thus the present data do not permit a conclusion that exchange programs are necessary to reduce risk behavior leading to HIV infection. However, the possibility of alternative methods for reducing injection risk behavior does not imply that an exchange program is not effective in reducing such behavior.
Nevertheless, the fact that very few new injectors participate in exchange programs may be considered a limitation on their current effectiveness. Since IDUs are typically exposed to hepatitis B and C within the first few years of injecting drugs (Hagan et al., 1993), new injectors may already be infected with these blood-borne viruses before they start to obtain sterile injection equipment from an exchange program. Moreover, in cities with high HIV-seroprevalence, even new injectors may be at high risk for HIV infection. In New York City, the estimated seroconversion rate among new injectors is 6.6 per 100 person-years at risk (Des Jarlais et al., 1994). The new injectors may become infected with HIV before they even begin to participate in an exchange program.
Sexual Risk Behavior. While all exchange programs address sexual transmission of HIV to some extent, fewer studies have examined the effect that the program has had on sexual-risk reduction among participants. Moreover, the findings from these few studies are ambiguous. Very few HIV prevention programs for injecting drug users have had consistent success in changing the sexual behavior of IDUs, particularly those with "regular" sexual partners (Friedman et al., 1994). The one exception might be programs that provide HIV counseling and testing, since drug injectors who know they are infected with HIV are more likely to change their behavior to reduce the chances of transmitting HIV to others (Vanichseni et al., 1993).
Effects on HIV and Hepatitis B Transmission. Research data on exchange programs has produced a body of consistent findings with regard to reduced risk behavior through drug injection. Studies within the programs of HIV seroprevalence and HIV seroincidence tend to validate the self-reported risk reduction. Seroprevalence rates have usually stabilized after a program has been implemented, and the rates of new infections among participants have ranged from zero to less than 1 per 100 person-years at risk to a moderate 4 per 100 person-years at risk in Amsterdam. While there is as yet no definite evidence that participation in a needle exchange reduces the chances of HIV infection, the available HIV seroprevalence and seroincidence data are largely consistent with this hypothesis.
The same behaviors that transmit HIV infection (multiperson use of injection equipment and unprotected sexual behavior) also transmit hepatitis B. The epidemiology of these viruses is similar in most countries, and injecting drug users are at high risk for infection with both viruses.
Studies on the effects of exchange-program participation and new hepatitis B infection among drug users in several cities have shown actual declines (Hagan et al., 1991), further validating self-reported risk reduction and indicating that exchange programs do have a large-scale effect on AIDS risk behavior among injecting drug users.
Discarded Syringes. Exchange programs create an economic value for used needles and sy-ringes—they can be traded for new injection equipment. Thus exchanges have the potential for reducing the amount of used and damaged equipment that is just discarded in the community. Indeed, the one study that systematically examined the amount of discarded injection equipment before and after implementation of an exchange program found a significant reduction in needles and syringes left on sidewalks and in the streets (Oliver et al., 1992)—where anyone might touch it and become a potential victim.
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