Among the 1822 MSM included in the analysis, 457 (25.1%) were circumcised. Circumcision prevalence differed by country: 378 (81.8%) men in the US were circumcised compared to 79 (5.8%) Peruvian men (). Circumcised men were older and had higher levels of education. Peruvian men reported higher numbers of sexual partners in the past year than US men, but there was little difference in the number of partners between circumcised and uncircumcised men within each country (12 vs. 10 in Peru and 5 vs. 6 in the US). Fewer circumcised men reported having a known HIV positive partner compared to uncircumcised men (1.5% vs. 1.6% in Peru and 17.1% vs. 24.1% in the US).
Demographic and behavioral and clinical characteristics of participants at enrollment
Uncircumcised men reported similar rates of new partners, less protected and unprotected receptive anal intercourse (PRAI and URAI), and more UIAI compared to circumcised men. Among Peruvian participants, the proportion of insertive acts with the last three partners was higher for circumcised than uncircumcised men (0.46 vs. 0.28), but among US participants, the proportion was similar between circumcised and uncircumcised men (0.53 vs. 0.51). A higher proportion of uncircumcised men reported exclusively receptive anal sex compared to circumcised men, particularly among Peruvian men (65.8% vs. 46.0%).
Drug use was more frequently reported by US than Peruvian participants (42.4% vs. 5.2%), particularly among uncircumcised men. Among US men, alcohol use was higher among circumcised men than uncircumcised men (45.2% vs. 36.1%). Uncircumcised men in both regions reported more sex in exchange for money, gifts or shelter than circumcised men (27.6% vs. 18.4% in Peru and 5.6% vs. 4.3% in the US).
Circumcision, Sexual Role and HIV Acquisition
Eighty-five men (67 uncircumcised and 18 circumcised) seroconverted to HIV (incidence 3.2/100 person-yrs). HIV incidence was 2.28 per 100 person-years (95% confidence interval [CI] 0.96, 4.56) during periods when men reported exclusively insertive sex.. In univariate analysis, being circumcised was not significantly associated with reduced HIV acquisition risk (risk ratio [RR]=0.84, 95% CI 0.50–1.42, p=0.512). In the pre-specified multivariate analysis, there was a non-statistically significant suggestion of a lower relative risk of HIV acquisition associated with circumcision for primarily insertive men (p-value for linear relationship by proportion of anal sex acts insertive=0.11) (). In this multivariate model, including the interaction between circumcision and proportion of sex acts that were insertive, the predicted relative risk of HIV acquisition associated with circumcision among men who were 80% insertive and exclusively insertive was 0.83 (95% CI 0.30–2.32) and 0.65 (95% CI 0.19–2.27), respectively. PAR percentages for lack of circumcision and HIV acquisition among men who were exclusively (100%) or mainly (80% of acts) insertive were 28.7% and 13.3%, respectively. These estimates differed by country, due to differences in circumcision rates: 55.9% and 48.8% in Peru and 8.9% and 3.6% in the US.
Multivariate relative risk of HIV acquisition for circumcised versus uncircumcised men under two modeled conditions
These data suggested a threshold for the relationship between circumcision status and insertive anal sex acts with HIV acquisition risk: circumcision was not protective for men who were primarily receptive (men who were insertive ≤60% of acts), but among men who were insertive for ≥60% of acts with recent partners, there appeared to be a non statistically-significant decreased risk for circumcised men compared to uncircumcised men (RR=0.31, 95%CI: 0.06–1.51). The interaction between these two categories (<60% vs. ≥60% insertive) and the circumcision effect was statistically significant (p=0.018). Based on this model, the PAR associated with circumcision among men who were primary insertive (≥60%) was 62.4% overall, or 74.0% and 28.7% in Peru and the US, respectively.