Background:  In North America and Europe, resurging epidemics of HIV infection have been identified among men who have sex with men (MSM). Here we report HIV incidence and associated risk factors in a cohort of MSM in Bangkok, Thailand.

Methods:  A longitudinal cohort study, with 3 years follow-up at 4-month intervals is underway. Presence of HIV-1 infection (baseline and follow-up) was determined by oral fluid testing (OraQuick), confirmed by 3 rapid blood tests, including enzyme immunoassay (EIA). At baseline, prevalence of herpes simplex virus-2 (HSV-2) and T. pallidum (TP) antibodies and rectal infection with C. trachomatis (CT) (by PCR) and N. gonorrhoeae (NG) (by culture) were determined. Circumcision status was assessed clinically at baseline, and demographic and behavioral data were collected every 4 months by audio-computer-assisted self-interview. Cumulative HIV incidence was estimated using Kaplan-Meier analysis. Risk factors for incident infection were evaluated using Cox proportional hazard analysis.

Results:  From April 5, 2006 to December 31, 2007, we enrolled 1292 men (mean age 26 years; range 18 to 56 years). The 22.4% (n = 290) who were HIV⁺ at baseline were excluded from further analysis. Among HIV^– (n = 1002), baseline prevalence of HSV-2 was 14.2%, and of TP, CT, and NG 2.7%, 7.2%, and 1.6%, respectively; 10.7% were circumcised. During the 4 months prior to enrollment, the mean number of male partners was 11.0 (median 5). Consistent condom use with male partners was 43.5 %. Receptive anal intercourse was practiced by 77.0%, and of these, 97.1% reported pre-intercourse rectal cleansing. Viagra use (ever) was reported by 7.3% and use of drugs for sexual pleasure (ever) by 12.9%. By December 1, 2008, 71 men had become HIV-infected (HIV incidence density of 5.7 per 100 person-years). Cumulative HIV incidence was 12.2%. Multivariate risk factors for incident HIV infection were younger age (≤21 years) (HR = 2.4, 95%CI 1.2 to 4.8), receptive anal intercourse (HR = 2.2, 95%CI 1.2 to 3.9), lack of condom use (HR = 2.1, 95%CI 1.3 to 3.4) and HSV-2 seropositivity at baseline (HR = 1.9, 95%CI 1.1 to 3.4).

Conclusions:  The high HIV incidence in this cohort of MSM in Bangkok documents an ongoing epidemic of HIV transmission in this population. The presence of known and modifiable risk factors, as identified in our analysis, underscores the need for additional effective interventions to stop the spread of HIV infection in MSM.