estimates of relative and absolute reduction in HIV incidence are based on mathematical models, Kaplan and his colleagues have explored the computational implications of a range of parameter values. These varied models provide estimates that are not dramatically different, lending credibility to the methods. Nevertheless, the models are not infallible.

The most compelling evidence from this set of evaluation studies is the direct evidence from the actual testing of syringes for the presence of HIV positivity. Here the empirical results of monthly assessments show about a one-third reduction in the rates of infected needles. These empirical results are consistent with those produced by the models underlying Kaplan's circulation theory. Furthermore, evidence about the actual operation of the needle exchange program reveals that the mechanisms necessary for change were in place. A substantial number of needles were exchanged (removed from circulation), the frequency of exchanging increased, and the mean circulation time of needles declined. Had these changes not occurred or had there been observed changes in the composition of the study population, the plausibility of the observed effect (i.e., reduction in the rate of infected needles) attributable to the program would have been undercut. Evidence about the program processes strongly suggests that the reduction in the rate of infected needles is plausibly due to the program. Similarly, reduction in the rate of infected needles strongly suggests (but does not directly test) that there should be a reduction in HIV incidence on the order of magnitude projected by Kaplan's models.

In the panel's view, the empirical data clearly indicate that needles used by program participants have a lower probability of being infected and, consequently, program participants are less likely to become infected.

The first legally authorized needle exchange program in the United States was implemented in Tacoma, Washington, in 1988. There are several reasons for examining the research on the Tacoma needle exchange in some detail. The needle exchange was the dominant HIV prevention effort in the local area, so there is less confounding with other simultaneous HIV prevention efforts than in other geographic areas. Also, several studies have been conducted on the Tacoma needle exchange program, making it possible to assess consistency across different outcome measures and study designs. As a U.S. city with an ethnically diverse population of injection drug users and high rates of both heroin and cocaine injection, Tacoma may be more relevant to the circumstances of other U.S. cities than the European and Australian cities in which other needle exchange programs have been implemented.

The importance of the Tacoma studies on needle exchange programs is

FRONT MATTER (R1-R18)

EXECUTIVE SUMMARY (1-8)

INTRODUCTION (9-20)

PART 1 DIMENSIONS OF THE PROBLEM (21-22)

1 THE EPIDEMIOLOGY OF HIV AND AIDS (23-56)

2 THE EPIDEMIOLOGY OF INJECTION DRUG USE (57-73)

3 NEEDLE EXCHANGE AND BLEACH DISTRIBUTION PROGRAMS IN THE UNITED STATES (74-102)

4 COMMUNITY VIEWS (103-142)

5 THE LEGAL ENVIRONMENT (143-164)

PART2 THE IMPACT OF NEEDLE EXCHANGE AND BLEACH DISTRIBUTION PROGRAMS (165-166)

6 THE EFFECTIVENESS OF BLEACH AS A DISINFECTANT OF INJECTION DRUG EQUIPMENT (167-197)

7 THE EFFECTS OF NEEDLE EXCHANGE PROGRAMS (198-262)

8 DIRECTIONS FOR FUTURE RESEARCH (263-278)

APPENDIXES (279-280)

A DESCRIPTION AND REVIEW OF RESEARCH PROJECTS IN THREE CITIES (281-306)

B PROFESSIONAL ASSOCIATION POSITIONS ON NEEDLE EXCHANGE AND BLEACH... (307-312)

C BIOGRAPHICAL SKETCHES (313-320)

INDEX (321-334)