WEPE298 - Poster Exhibition
Multi-encounter analysis of substance use, situational characteristics, and typologies of sexual outcomes in single-partner sexual encounters reported by MSM in England
G.J. Melendez-Torres1,2, F. Hickson3, D. Reid3, P. Weatherburn3, C. Bonell2
1Centre for Evidence-Based Intervention, Department of Social Policy and Intervention, University of Oxford, Oxford, United Kingdom, 2Social Science Research Unit, Institute of Education, University of London, London, United Kingdom, 3Sigma Research, London School of Hygiene and Tropical Medicine, London, United Kingdom
Background: Men who have sex with men (MSM) in England use
recreational substances at rates higher than the overall population. This substance use commonly co-occurs with sex. Though multi-encounter evidence from the
United States suggests substance use is associated with sexual risk among MSM, findings
are inconsistent across studies and no such evidence exists for MSM in England. Compared to single-encounter or person-level
analyses, analysis of multiple sexual encounters per respondent better captures
encounter-level associations between substance use, situational variables (e.g.
place of sex), and sexual behaviour by addressing person-level confounding and
Methods: Throughout 2011 and early 2012, MSM in England took
part in a longitudinal web-based survey in which they reported up to five sexual
encounters with another man. Multilevel
models measured whether respondent substance use, place of sex, relationship
with partner, or seroconcordance were associated with unprotected anal
intercourse (UAI). A multilevel latent
class model with substance use and situational variables as manifest indicators
and UAI as a distal outcome was also specified.
Results: 2,142 MSM reported 6,742 eligible encounters. In univariate multilevel models, respondent substance
use (OR=2.02, p< 0.001), number of substances used (OR=1.64, p< 0.001), and
use of each of poppers, crystal methamphetamine, and GHB (all p< 0.05) were positively associated
with UAI. UAI was less probable with
anonymous (OR=0.16, p< 0.001) or serodiscordant (OR=0.31, p< 0.001) partners,
and in sex-on-premises venues (OR=0.48, p< 0.001). Multivariate models including a substance use
measure and situational variables yielded similar effects.
A three-class model was selected. Class 1 (31.5% of encounters, UAI probability
41.5%) reflected at-home encounters, steady partners and little substance
use. Class 2 (61.8% of encounters, UAI
probability 23.0%) reflected non-steady/anonymous partners and little substance
use. Class 3 (6.7% of encounters, UAI
probability 52.9%) was defined by polysubstance use. Overall differences in UAI probability were
statistically significant (p< 0.001).
Conclusions: This study mirrors other multi-encounter studies
finding significant relationships between substance use and UAI. It extends previous studies by examining
substance use and situational characteristics through latent class modelling. Future studies should examine specific
substances more closely and continue developing interventional approaches to
reduce substance use-associated sexual risks.
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