Although the three models differ in many ways, the primary distinguishing factors are as follows. The simplified circulation model focuses on obtaining estimates of averted HIV infections among program participants, based on a 1-year time frame, attributable to transmission from sharing contaminated needles. The behavior change model estimates averted infections among all injection drug users in the community as well as their sexual partners and offspring over a 5-year time interval, attributable to transmissions from both sharing and sexual behavior. The combined circulation and behavior change model incorporates characteristics of both models.

As depicted in Table 3.2, all models estimated that the hypothetical needle exchange program had a substantial impact on averted HIV infections and reported significantly lower costs per HIV infection averted than the $119,000 estimated lifetime HIV medical costs associated with treating a person infected with HIV (Hellinger, 1993). One noticeable disparity is the substantially different estimates in the number of infections averted over 5 years reported by the behavior change model compared with the combined model. This disparity is due mainly to the fact, as with the circulation model, that the combined model limits its estimates to infections averted among program participants only (participants are assumed to share only with each other).

These are obviously crude estimates of the cost-effectiveness of needle exchange programs and are of limited value in assisting health policy makers

TABLE 3.2 Comparison of Three Model Estimates of Needle Exchange Impact and Cost-Effectiveness

 

Simplified

Circulation Model

Behavior Change

Model

Combined Model

Absolute HIV infection averted

50

46

53

Additional absolute HIV infection averteda

0

113

11

Cost per HIV infection avertedb

$12,000

$3,773

$9,375

a Estimated drug-related (i.e., direct sharing) HIV infections averted in program participants during 1 year of program participation.

b Estimated drug-related and sexually related HIV infections averted among program clients, their drug and sexual partners, and their offspring over 5 years. That is, 1 year of program operation and 4 years of delayed effects (averted infections during the 1 year of program operation among program participants due to sharing are not included).

SOURCE: Adapted from The Public Health Impact of Needle Exchange Programs in the United States and Abroad, Volume 1 (Lurie et al., 1993a:499).



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