Exposure-response relationship between the number of anal sex partners and prevalent HIV, HSV-2 and syphilis infections among men who have sex with men

Objective: To identify the exposure-response relationships between the number of anal sex partners and the prevalence HIV, HSV-2 and syphilis infections.

Methods: A cross-sectional survey was conducted among MSM having anal sex activities in the past six months in Shanghai from April 2008 to September 2009. A generalized linear mixed model with negative binomial distribution was used to examine the fixed effects. Exposure-response relationships were fitted by exponential curves.

Results: Among 1072 participants whose average age was 28.2(±8, range of 18-66) years, less than half (43%) persisted in condom use, the majority (60%) were self-identified homosexuals and approximately one-third (36%) were bisexuals. The prevalence of HSV-2, HIV, current syphilis and co-infections were 10.4%, 7.8%, 7.4% and 3.9%, respectively. A greater number of sex partners was associated with higher income), lower education level and commercial sex activity. In those without persistent condom use, a significant and accelerated increase in sexually transmitted infections (STIs) prevalence was associated with an increase in the number of sex partners. The prevalence of HSV-2 (25.6% - 30.1%), syphilis (23.0% - 27.7%) and HIV (21.5% - 25.7%) was very high while MSM had over 20 sex partners with unprotected anal intercourse in the past six months. However, the exposure-response relationships didn't exist in those using condom persistently.

Conclusion: Having multiple sex partners without persistent condom use is common among MSM in Shanghai, which is leading to the epidemic of HIV, HSV-2 and syphilis. It provides an evidence to develop effective intervention strategies for STIs prevention among MSM.