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Behavioral, Biological and Structural
Components of MSM STI Morbidity
Steven Goodreau and Matthew Golden
University of Washington CFAR
HIV/AIDS in MSM
2002 Diagnoses of HIV/AIDS, by exposure category
0
2,000 4,000 6,000 8,000 10,000 12,000 14,000
Male-to-male sexual contact
Heterosexual contact - females
Heterosexual contact - male
IDU - Males
IDU - females
Male-to-male sexual contact & IDU
Perinatal
Source: CDC HIV/AIDS Surveillance Report Vol. 14, 2002
Why?
Behavioral explanations:
•Numbers of partners
•Condom use
Why?
Behavioral explanations:
•Numbers of partners
•Condom use
Biological explanations:
•Transmissibility
Why?
Behavioral explanations:
•Numbers of partners
•Condom use
Biological explanations:
•Transmissibility
Structural explanations:
•Two-sex vs. one sex
•Population size
•Versatility
•Assortative mixing
Thought experiment
How large a difference in epidemics might occur
between MSM and heterosexual populations that are
identical in behavioral characteristics, but
differ in structural and biological characteristics?
Explore using a mathematical model and data on MSM
sexual behavior from UMHS (1995).
Partners in past twelve months
% with 0 partners
% with 1 partner
80
% with 2+ partners
70
60
50
40
30
20
10
0
all males - any
sex
Median = 1
All males: NHSLS (random sample of US adults)
MSM: UMHS (random sample of MSM in four large US cities)
Partners in past twelve months
% with 0 partners
% with 1 partner
80
% with 2+ partners
70
60
50
40
30
20
10
0
all males - any
sex
MSM - any sex
Median = 1
Median = 3
Mean = 10.9
All males: NHSLS (random sample of US adults)
MSM: UMHS (random sample of MSM in four large US cities)
Partners in past twelve months
% with 0 partners
% with 1 partner
80
% with 2+ partners
70
60
50
40
30
20
10
0
all males - any
sex
MSM - any sex
MSM - anal sex
Median = 1
Median = 3 Median = 1
Mean = 10.9 Mean = 4.0
All males: NHSLS (random sample of US adults)
MSM: UMHS (random sample of MSM in four large US cities)
Partners in past twelve months
% with 0 partners
% with 1 partner
80
% with 2+ partners
70
60
50
40
30
20
10
0
all males - any
sex
MSM - any sex
Median = 1
Median = 3 Median = 1
Mean = 10.9 Mean = 4.0
MSM - anal sex
MSM - unprot.
anal
Median = 0
Mean = 1.3
All males: NHSLS (random sample of US adults)
MSM: UMHS (random sample of MSM in four large US cities)
Model basics
Deterministic Compartmental
Seronegative
Seropositive
Subdivided into compartments based on:
Activity level
Role
No activity
Low activity
High activity
Insertive (male)
Receptive (female)
heterosexual pop.
Versatile
Insertive
Receptive
MSM pop.
Model features
Sources:
•Activity levels:
•Roles:
none
62.8%
low (1 partner per year)
15.5 %
high (7.7 partners per year) 21.7 %
MSM:
heterosexuals:
versatile 50%
insertive 35%
receptive 15%
insertive
receptive
•Mixing by level: 16.6 times more likely to choose
partners of the same activity level
than expected by chance
50%
50%
UMHS
UMHS
NHSLS
Model features
Transmissibility/
act:
unprot. receptive anal
unprot. insertive anal
unprot. receptive vaginal
unprot. insertive vaginal
0.00500
0.00065
0.00100
0.00050
Acts/
partnership:
10 (for high-high)
50 (for high-low)
250 (for low-low)
•Size:
small = 1,000; large = 10,000
•Removals:
sero-ves: 30 years after entry
sero+ves: 7.5 years after
seroconversion
•Arrivals:
equal in number to removals
Sources:
Varghese
et al. 1992
UMHS
Results - HIV prevalence
0.25
MSM - all versatile
small pop, anal transmissibility
HIV prevalence
0.2
0.15
0.1
0.05
0
0
25
50
75
year
100
125
150
Results - HIV prevalence
0.25
MSM - all versatile
small pop, anal transmissibility
HIV prevalence
0.2
0.15
Heterosexual or MSM-no versatile
small pop, anal transmissibility
0.1
0.05
0
0
25
50
75
year
100
125
150
Results - HIV prevalence
0.25
MSM - all versatile
small pop, anal transmissibility
HIV prevalence
0.2
MSM – observed versatility
small pop, anal transmissibility
Heterosexual or MSM-no versatile
small pop, anal transmissibility
0.15
0.1
0.05
0
0
25
50
75
year
100
125
150
Results - HIV prevalence
0.25
MSM - all versatile
small pop, anal transmissibility
HIV prevalence
0.2
MSM – observed versatility
small pop, anal transmissibility
Heterosexual or MSM-no versatile
small pop, anal transmissibility
0.15
0.1
Heterosexual
large pop, anal transmissibility
0.05
0
0
25
50
75
year
100
125
150
Results –HIV prevalence
0.25
MSM - all versatile
small pop, anal transmissibility
HIV prevalence
0.2
MSM – observed versatility
small pop, anal transmissibility
Heterosexual or MSM-no versatile
small pop, anal transmissibility
0.15
0.1
Heterosexual
large pop, anal transmissibility
0.05
0
0
25
50
75
year
100
125
Heterosexual
large pop, vaginal transmissibility
150
Results (cont.)
In order to have the same HIV prevalence as MSM
after the first 20 years of the epidemic, heterosexuals
would need to have 4.4 times as many partners as
MSM on average.
Results (cont.)
MSM are more susceptible to high risk behavior by a small
subset of the population.
Results (cont.)
MSM are more susceptible to high risk behavior by a small
subset of the population.
If the partnering rates of the high-activity group are doubled:
Results (cont.)
MSM are more susceptible to high risk behavior by a small
subset of the population.
change in HIV prevalence
compared to observed activity
levels
If the partnering rates of the high-activity group are doubled:
1200%
MSM
1000%
800%
prevalence at year 20
of the epidemic is
changed by
600%
975% in MSM
170% in heterosexuals
400%
200%
Het
0%
0
5
10
year
15
20
Implications
•Structural and biological factors can play major roles in increasing
susceptibility of MSM populations to HIV.
Implications
•Structural and biological factors can play major roles in increasing
susceptibility of MSM populations to HIV.
•The public health community should not assume that persistent
differences in HIV/STD levels between MSM and heterosexuals are
due only (or even primarily) to differences in individual behavior.
Implications
•Structural and biological factors can play major roles in increasing
susceptibility of MSM populations to HIV.
•The public health community should not assume that persistent
differences in HIV/STD levels between MSM and heterosexuals are
due only (or even primarily) to differences in individual behavior.
•MSM will remain relatively vulnerable to HIV/STD epidemics even
with major shifts in behavior.
Implications
•Structural and biological factors can play major roles in increasing
susceptibility of MSM populations to HIV.
•The public health community should not assume that persistent
differences in HIV/STD levels between MSM and heterosexuals are
due only (or even primarily) to differences in individual behavior.
•MSM will remain relatively vulnerable to HIV/STD epidemics even
with major shifts in behavior.
•What about Africa?
higher infectivity
other structural patterns not modeled here
nosocomial
Implications
•Structural and biological factors can play major roles in increasing
susceptibility of MSM populations to HIV.
•The public health community should not assume that persistent
differences in HIV/STD levels between MSM and heterosexuals are
due only (or even primarily) to differences in individual behavior.
•MSM will remain relatively vulnerable to HIV/STD epidemics even
with major shifts in behavior.
•What about Africa?
higher infectivity
other structural patterns not modeled here
nosocomial
•More broadly, factors other than numbers of unsafe partners can
predispose or protect different populations from STD epidemics.
Acknowledgments
University of Washington CFAR
King Holmes
Martina Morris
Mark Handcock
The entire staff of CAPS’ Urban Men’s Health Study
Joseph Catania
Ron Stall
Tom Coates
The participants in the Urban Men’s Health Study