Julienne McKay, David Campbell and Anna Cornelia Gorter (presenter) IAEN Symposium

1. Can targeted, high-cost STI treatment contribute to cost-effective HIV prevention in developing countries? Julienne McKay, David Campbell and Anna Cornelia Gorter (presenter) IAEN Symposium TorontoSaturday 12 August 2006

2. Outline of presentation • Capturing actual impacts from STI treatment programs • Program and delivery mechanism • Strong evidence that program lowered STI prevalence • Measuring program impacts • Can targeted, high-cost STI treatment contribute to cost-effective HIV prevention strategies?

3. Capturing program impacts • Strong evidence that STIs increase individual HIV infectivity and susceptibility • Difficult to prove effectiveness of STI programs in reducing HIV spread • One concern lies with limited evidence of effectiveness of high-efficacy treatment in delivering and sustaining reductions in STI prevalence in populations most at risk • One explanation lies in high rates of reinfection in these populations

4. Capturing program impacts • Constraint on effectiveness of STI treatment programs • Possibly greater constraint on ability to measure true impact of programs • especially given reliance on diagnostic data collected at time of treatment • Analysis demonstrates that this measure prone to serious underestimation of intervention impacts

5. Capturing program impacts • Time at which STI prevalence measured not representative of average STI prevalence • prevalence between previous treatment and current testing • Measure most relevant to program’s impact on HIV susceptibility and infectivity • Developed methodology that tests and adjusts for bias in measured STI prevalence • using historical data and capitalising on chance variations in time intervals between treatments

6. Program Nicaragua 1996-2005 • Objectives: • complement behaviour change programs • reduce HIV transmission risks by lowering average STI prevalence among sex workers, partners, clients and MSM • Mechanism: • clinic based diagnosis, high efficacy treatment • treatment provided at intervals ranging from 3 to 9 months • safe sex education plus VCT and follow-up of HIV+ individuals

7. Program Nicaragua 1996-2005 • Instrument: • competitive voucher program • allows tight targeting • market mechanisms assist cost control • financial incentives for clinics to deliver high quality services efficiently • In 2005, HIV prevalence remained low • 0.1% - 0.3% in adult population • <3% among sex workers

8. Strong evidence that program lowered STI prevalence • Chance variations in timing between treatment rounds allowed attribution to program of sustained reduction in measured STI prevalence among sex workers redeeming vouchers • Trends in condom use and use of non-program STI treatments added virtually nothing to highly statistically significant relationship between changes in time period between commencement of treatment rounds and changes in measured STI prevalence. • Results reported in AJPH 2006, 96:7-9

9. Measuring program impacts • Simulation model mirrors operation of program and use of other STI treatment regimes with and without the program • allows estimation of ‘steady state’differential in average STI prevalence • Uses Markov mechanism to track individual sex workers over 20 rounds (1996-2005) • aggregates individual results to population estimates • initial ‘Markov states’ defined by a sex worker’s STI status and condom use at time program introduced • simulation of each round determines sex worker’s ‘Markov state’ at start of next round • Program data used to estimate event probabilities

10. Measuring average STI prevalence • STI reinfection specified within model using Bernoulli mechanisms • allows for adjusting within-round reinfection rates to changes in timing between rounds • reinfection calibrated to measured STI prevalence before start of next treatment round

11. Program Impacts: STI Prevalence, 1996-2005 25% R7 Measured STI prevalence at commencement of round R1 R9 R6 R5 20% R3 R12 R10 R8 R11 15% R13 R14 R2 STI Prevalence R17 R15 R16 R20 10% R18 Average STI prevalence between rounds 5% Based on 2 STIs - syphilis and trichamonas - for which program had continuous consistent data 0% Months

12. STI differential becomes key input into model of HIV spread • Model identifies minimum reduction in HIV prevalence among sex workers, clients and partners that program needs to deliver in order to justify its costs • Via its modelling of STI/HIV infectivity link, calculates threshold reduction in STI rates that program must deliver • Also used to estimate net financial benefits from program’s continuation

13. Direct financial benefits well in excess of program costs Note: 3% discount rate applied to both financial benefits and program costs

14. Outline of methodology

15. Relation between timing of treatment rounds and measured STI prevalence at commencement of each round

16. Managing high levels of uncertainty in parameter values 1. Plausible ranges for key parameters, or sets of parameters, identified from: • literature • data collected through doctors’ interviews with voucher redeemers • clinical diagnosis and laboratory analysis in each treatment round • Starting parameter values drawn from these ranges • erred towards underestimating program impacts

17. Managing high levels of uncertainty in parameter values 2. Set boundary conditions: measured STI and HIV rates; stability of HIV rates through time; condom use; time periods between treatment rounds and established link to STI prevalence at start of next round represented ‘boundary conditions’ • Used to test for any feasible departures from starting parameter values that were also consistent with known population characteristics • Boundary conditions allowed us to define a reduced subset of plausible parameter estimates

18. Managing high levels of uncertainty in parameter values 3. Across this subset, probed scope for different parameter values yielding substantially different program outcomes: • in general, tightly constrained by boundary conditions • Despite remaining uncertainty about individual parameter values, could draw robust conclusions concerning key drivers of program value: • the reduction in average STI prevalence among sex workers • the lower bound on the associated reduction in HIV prevalence among sex workers, clients and community

19. How does a voucher program operate?

20. Advantages of voucher programs • Tight targeting of populations at high risk • Greater equity in accessing health resources • purchasing power given to the individual • Utilises existing health sector resources • does not require large-scale upfront (public or private) investment in infrastructure or human resources • value attached to voucher only when redeemed • Potential to: • lead to better health sector resource allocation • generate economies of scale for providers

21. Competitive voucher program yields additional advantages • If providers tenderagainst protocol and quality assurance requirements, limits costs • If prices set by voucher agency, providers compete on service quality • total level of funding received by each provider determined by number of vouchers redeemed • Potential to: • increase service quality for all users • increase efficiency of service delivery

22. More information: www.icas.net julienne.mckay@gmail.com anna@icas.net zoyla@icas.net