Background: Since the first official report of AIDS in
the United States, men who have sex with men (MSM) have been and
remain at substantial risk for HIV infection. Unprotected anal
intercourse (UAI) is a primary risk factor for HIV acquisition and
transmission among MSM.
Objective: To explore key behavioral and structural
factors associated with UAI among Internet-using MSM aged 18 years
and older, and estimate the relative association of each factor by
accounting for the natural heterogeneity between subjects.
Methods: A prospective longitudinal online study was
conducted from May 2010 through December 2011 in United States. 652
Internet-using MSM aged 18 years and older, having at least one
male sex partner in past 12 months, and recruited from social
networking Web sites were followed for 12 months with six
self-administered interviews. Logistic regression was used to model
frequencies of UAI experiences among MSM with independent
variables. A generalized linear mixed modeling was used to estimate
parameters and test for significant variations in risk of UAI
between study participants.
Results: The factor most strongly associated with
reporting UAI was number of male sex partners in the past 12
months. In multivariate analysis, compared with a man who reported
a single male sex partner in past 12 months, a man who reported
> 5 male sex partners (aRR=8.5, P <.0001) and a man
who reported having three to five male sex partners (aRR=5.1,
P <.0001) were at increased risk of engaging in UAI.
Other factors that were independently associated with reporting UAI
were experience of physical violence with a current male sex
partner (aRR=1.7, P = 0.03) and meeting at least one male
sex partner on Internet (aRR= 2.1, P = 0.002).
Conclusions: Comprehensive HIV prevention packages for
MSM should address number of sex partners and intimate partner
violence. More focused studies are needed to investigate the
relationship between Internet use for meeting male sex partners and