Annick Borquez, Ph.D., a specialist on using mathematical modeling to estimate the contribution of different sources of risk to HIV incidence in various populations and settings, spoke on a Sept. 3 webinar hosted by the Network for Multidisciplinary Studies on ARV-Based HIV Prevention (NEMUS). She discussed a mathematical model for estimating the effectiveness and cost-effectiveness of various HIV-prevention approaches among transgender women sex workers (TWS) in Lima, Peru. This is a substudy of a larger study of HIV prevention models among men who have sex with men (MSM) and transgender women (TW) in Peru. The mathematical model is the third phase of the study, and was preceded by a stakeholder analysis and a capacity analysis of the Peruvian health system.
The model is based on the following estimates:
- A population of 20,000 TW in Lima;
- 27% HIV prevalence in the TW population;
- 65% to 70% of TW engaged in sex work;
- 25 to 30% of HIV-infected MSM and TW receiving antiretroviral therapy (ART);
- 75% of sex workers using condoms with clients;
- 25% of TWS having stable non-commercial partners (defined as relationships lasting longer than six months);
- 60-year life expectancy among TW in Peru.
Twenty-three different combinations of the following interventions were considered in the model:
- Increasing relative condom and lubricant use 15% with clients over three years;
- Increasing relative condom and lubricant use 10% with stable partners over three years;
- Scaling up ART for CD4+ cell counts below 500, leading to 60% of HIV-infected TWS on HIV treatment;
- Offering "test and treat" approach to ART independent of CD4+ cell count, leading to 80% of HIV-infected TWS on treatment;
- Offering pre-exposure prophylaxis (PrEP), with 15% coverage among TWS after five years (adherence estimated to be about half).
All interventions assume a substantial increase in the current 25% HIV-testing rate in this population. The cost of HIV testing was folded into the cost of the various treatment interventions, but the cost of social interventions -- such as combatting stigma and discrimination -- was not included in the model.
According to the model, the highest number of HIV infections averted over 10 years (4,500) would be achieved if all interventions were combined. This would also cost the most, especially considering the current price of tenofovir/emtricitabine (Truvada), the drug used for PrEP (US$ 120/month). The Peruvian government is negotiating a discount, which may reduce the price to US$ 30/month.
The model suggests that averting 50% of new HIV infections over the next 10 years could be achieved or almost achieved with any one of these combined approaches:
- Increased client condom use plus PrEP plus ART at CD4+ cell count ≤ 500;
- Increased client condom use plus "test and treat" (ART at CD4+ cell counts > 500);
- Increased client condom use plus ART at CD4+ cell counts ≤ 500.
In 2014, Peru spent almost 282 million nuevo soles (US$ 88 million at current rate of exchange) on HIV prevention and treatment. The most cost-effective approach would be option 3, at an estimated cost of 11 million nuevo soles over 10 years. Ms. Borquez cautioned, however, that "intervention access and uptake among this marginalized population requires an improvement in their environment."