Table 1 Illustrative example for assessing whether a local SSP is cost-saving to society

Size of the local PWID population

 There has not been any formal study to estimate the size of the local PWID population. Estimates for local experts—the Health Department, substance use treatment staff, local hospital staff, law enforcement, and the SSP staff themselves range from 3000 to 7000, with an average estimate of 5000 PWID active an any point in time

Is HIV transmission among PWID under control in the local area?

 HIV testing is readily available in the area

 The SSP, the substance use treatment programs, and the local health department all offer no cost HIV testing. The health department does conduct HIV surveillance based on the widespread availability of testing

 The number of newly identified cases of HIV infection among persons with injecting drug use as their transmission risk (a surrogate measure of incidence) has remained stable at 50 ± 10 per year over the last 5 years. The number of PWID living with HIV (a proxy measure of HIV prevalence) is approximately 500 and has been growing slightly, as there are relatively few deaths among PWID infected with HIV. (This measure can be estimated by subtracting known deaths among PWID infected with HIV from the total of PWID diagnosed with HIV over time.)

 Conclusion: HIV transmission among PWID is under control in the area

Is the SSP “functioning very well?

 The SSP distributes about 500,000 syringes per years. It works on a non-strict 1 for 1 model and encourages secondary exchange

 Persons obtaining large numbers of syringes for secondary exchange are required to bring in large numbers of used syringes

 The SSP program provides “starter kits” so that all participants leave the exchange with some sterile syringes even if they did not have any used syringes to bring to the exchange

 Some pharmacies in the area also sell syringes to persons who inject drugs

 Informal interviews with SSP participants, persons entering substance abuse treatment, and PWID in the community indicate that PWID believe they have very good access to sterile syringes, and that sharing because of a lack of sterile syringes is a rare event

 The SSP does have staff assigned to assist PWID to access substance use treatment and to assist HIV seropositive PWID to access ART. The staff can make initial intake appointments for PWID at both substance use and ART programs, but do not have the capability to track persons who fail to show for their intake appointments

 SSP staff regularly but informally interview program participants about whether the SSP is meeting their needs of sterile syringes and changes in drug use patterns in the community. SSP outreach workers also informally interview PWID in the community about access to sterile syringes and about changes in the patterns of drug use

 Conclusion: The SSP is functioning very well

Cost-saving calculation

 If the SSP budget is $500,000 per year, then the minimum number of new HIV infections that would need to be prevented is $500,000/$229,899 = 2.2, which rounds up to 3

 Conclusion: The minimum cost-savings threshold would be averting 3 additional new infections per year

Is the SSP cost saving to society?

 This question can be rephrased as: Given that there is some ongoing transmission of HIV in the community, if we reduced the supply of sterile syringes by 500,000 per year in a PWID population between 3000 and 7000, would we expect to see more than 3 additional HIV infections per year in the local PWID population?

 All epidemiologic models that we are aware of would answer the question with a definite: Yes, reducing the supply of sterile syringes by this amount would definitely lead to more than 3 new HIV infections per year

 Common experience with SSPs and HIV transmission in PWID populations would also indicate that such a large reduction in the supply of sterile syringes would generate more than 3 additional incident cases of HIV infection per year in the PWID population