Background: PrEP is recommended for HIV prevention among at risk men who have sex with men (MSM) in Thailand. Anticipated PrEP impact on reduction of HIV infections would support the expansion of programs implementing PrEP in combination with consistent condom use. We used a deterministic model to assess PrEP and condom use and estimated HIV infections among MSM in Bangkok, Thailand using different adherence attributes.
Methods: For this deterministic model previously developed by Smith et al, we used three parameters from published data: 1) PrEP effectiveness from the iPrEx international clinical trial among MSM having < 50% adherence and ≥90% adherence based on self-reported medication adherence and pill counts 2) condom effectiveness from self-reported condom use during anal sex among MSM reporting at least one HIV-positive partner in two prospective HIV prevention trials and 3) annual HIV incidence in the absence of PrEP from the Bangkok MSM Cohort study, overall and stratified by characteristics. Among different age groups and risk behaviors, and adherence categories, the number of HIV infections per 10,000 MSM each year was calculated. The estimates assumed that PrEP and condom use efficacy were independent.
Results: Among MSM who had ≥90% PrEP adherence, an estimated 46 (19-110) HIV infections would occur among those who used condoms consistently; and an estimated 590 (520-680) HIV infections would occur among those not taking PrEP and not using condoms (a reduction of 544 HIV infections). Among MSM who had < 50% PrEP adherence, an estimated 116 (52-260) HIV infections would occur if condoms were used consistently. Combination HIV prevention used in MSM who were ages 18-21 years, or who engaged in sex parties, or who used club drugs with sex resulted in the greatest reduction of HIV infections (a reduction of 811, 922, and 1493 HIV infections) compared to those not using PrEP and condoms.
Conclusions: Models predict an estimated >10 fold reduction of HIV infections each year for MSM using PrEP and condoms in Bangkok, Thailand. Adherent combination prevention strategies in the highest risk MSM could result in the most substantial reductions in HIV infection.