Background: Post-exposure prophylaxis (PEP) is an emergency chemoprophylactic intervention after an exposure to viral inoculum. Stimulant-using (SU) MSM are at high risk of HIV acquisition, but are a challenging population in which to implement PEP. CM is a robust intervention that provides voucherbased incentives for stimulant-use abstinence, and has been shown to be a powerful and durable substance-use intervention. We previously reported that in a single-arm pilot intervention of PEP combined with CM in methamphetamine-using MSM, time to PEP initiation, adherence, and course completion rates were not different from historical non-SU populations.
Methodology: We conducted a prospective, randomized controlled trial of CM with PEP among SU MSM at a single site in Los Angeles, California. Participants enrolled in the study were randomized to CM or non-contingent (NC) control behavioral intervention and followed prospectively. Generalized linear models were used to estimate the effect of CM on likelihood of PEP course completion, rates of medication adherence, stimulant use and selfreported sexual risk behaviors. All analyses controlled for participant sexual identity, race/ethnicity, housing status, and income.
Results: Between June, 2010 and June, 2012, 140 MSM individuals were enrolled and randomized to CM (n=70) or a NC (n=70) behavioral intervention. The participants were 37% Caucasian, 37% African American, and 18% Latino. Mean age was 36.8 (SD 10.2) years, 61% had high school education or less, and 88.4% reported an annual income ≤$30,000. 45 participants (32%) initiated PEP after a high-risk sexual exposure during the study period, with a mean exposure-to-PEP time of 35.2 hours. 29 of the 45 had evaluable adherence data. PEP course completion was significantly greater in the CM arm compared to the NC arm (AOR 7.2, 95% CI 1.1-47.9), and there was a trend towards improved medication adherence by self-report in the CM arm (AOR 4.33, 95% CI 0.76-21.86). CM participants had a greater probability of stimulant-free urine specimens vs. NC participants (IRR 1.57, 95% CI 1.12-2.22), and a trend towards reduced episodes of UAI (IRR 0.34 [95% CI 0.11-1.08). One HIV seroconversion was observed in the context of repeat exposures, and is unlikely to represent PEP failure.
Conclusions: In a randomized, controlled trial of SU MSM, CM facilitated the use of PEP by increasing rates of course completion, and suggesting a trend toward improved adherence. Reductions in sexual risk afforded by the CM intervention are a prime example of HIV prevention synergy. Despite small numbers of individuals initiating PEP, findings suggest that CM may be a useful support mechanism for the use of PEP, and potentially other biomedical prophylactic strategies in stimulant-using MSM.