Early predictors of seroconversion among enrolees in a PrEP program in Brazil, Mexico and Peru ' the IMPREP Demonstration study


BACKGROUND: ImPrEP, a PrEP Demonstration Project for men who have sex with men (MSM) and transwomen in public health facilities in Brazil, Mexico and Peru, started enrolling mid-2018 and as of December 2020 included 3842, 3005 and 2265 participants, respectively. Since PrEP effectiveness requires personal commitment, PrEP programs should offer additional support to people more likely to seroconvert. In this analysis we assessed seroconversion in the cohort and modeled its early predictors.
METHODS: ImPrEP enrolled consenting, HIV negative MSM and transwomen 18+ y.o. reporting recent (within 6 months): condomless anal sex; HIV positive/unknown status sex partner; STI diagnosis or signs/symptoms; or transactional sex. Enrolled participants received 30-days of PrEP and returned at 1-month for a safety visit; subsequent prescriptions and visits were quarterly, all visits included HIV testing and behavioral assessments. Adherence was measured using the medication possession ratio (MPR): the number of pills prescribed divided by the days between visits. Anyone who tested HIV-positive post-enrollment were withdrawn from the cohort and linked to HIV care. Cox regression was used to identify early predictors of seroconversion, including baseline socio-demographics and behaviors, plus MPR at the 1-month visit; the multivariate Cox model included all variables with p values <0.1, controlling by gender and country.
RESULTS: Seroconversions by country, population and age group are shown in Table 1 below. In the multivariate Cox model, risk of seroconversion was associated with being 18-24 y.o. (aHR 4.8, 95%CI 2.3-10.1), condomless receptive anal sex (aHR 2.0, 95%CI 1.1-3.6), MPR of 0.53-1 (aHR 2.8, 95%CI 1.5-4.9); MPR<0.53 (aHR 3.7, 95%CI 1.8-7.6), and being from Peru (aHR 4.0, 95%CI 2.0-7.9), controlling for gender, transactional sex, and initial intention to use PrEP.

Table 1. Seroconversions by Country, Population and Age Group.
CountryMSM 18-24
n [rate (95% CI)]
TW 18-24
n [rate (95% CI)]
MSM 25+
n [rate (95% CI)]
TW 25+
n [rate (95% CI)]
n [rate (95% CI)]
Brazil10 [0.87 (0.42-1.61)]1 [1.94 (0.05-10.81)]4 [0.1 (0.03-0.26)]0 [0.00 (0.00-2.82)]15 [0.28 [0.16-0.47)]
Mexico4 [1.16 (0.32-2.97)]0 [0.00 (0.00-49.92)]7 [0.4 (0.16-0.82)]0 [0.00 (0.00-18.01)]11 [0.52 (0.26-0.92)]
Peru22 [4.05 (2.54-6.13)]4 [9.47 (2.58-24.24)]17 [1.71(0.99-2.73)]3 [1.71 (0.35-5.00)]46 [2.62 (1.92-3.49)]
TOTAL36 [1.77 (1.24-2.45)]5 [4.94 (1.60-11.53)]28 [0.42 (0.28-0.6)]3 [0.92 (0.19-2.68)]72 [0.79 (0.62-0.99)]

CONCLUSIONS: The risk for seroconversion in ImPrEP was associated with younger age (18-24), being from Peru, reporting condomless receptive anal sex, and early signs of non-adherence (low MPR). Strategies are needed to support enrollees with these criteria to remain adherent and prevent seroconversion.