Behavioral, Biological and Structural Components of MSM STI Morbidity Steven Goodreau and Matthew...

Behavioral, Biological and StructuralComponents of MSM STI Morbidity

Steven Goodreau and Matthew GoldenUniversity of Washington CFAR

HIV/AIDS in MSM

2002 Diagnoses of HIV/AIDS, by exposure category

Source: CDC HIV/AIDS Surveillance Report Vol. 14, 2002

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

Why?

Behavioral explanations:

•Numbers of partners•Condom use

Why?



Biological explanations:

•Transmissibility

Why?



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

All males: NHSLS (random sample of US adults)MSM: UMHS (random sample of MSM in four large US cities)

0

10

20

30

40

50

60

70

80

all males - anysex

% with 0 partners

% with 1 partner

% with 2+ partners

Median = 1



0

10

20

30

40

50

60

70

80

all males - anysex

MSM - any sex

% with 0 partners

% with 1 partner

% with 2+ partners

Median = 1 Median = 3Mean = 10.9



0

10

20

30

40

50

60

70

80

all males - anysex

MSM - any sex MSM - anal sex

% with 0 partners

% with 1 partner

% with 2+ partners


Median = 1Mean = 4.0




0

10

20

30

40

50

60

70

80

all males - anysex

MSM - any sex MSM - anal sex MSM - unprot.anal

% with 0 partners

% with 1 partner

% with 2+ partners



Model basics

Sero- negative

Subdivided into compartments based on:

Activity level

No activityLow activityHigh activity

Sero- positive

Role

Insertive (male)Receptive (female)

VersatileInsertiveReceptive

Deterministic Compartmental

heterosexual pop.

MSM pop.

Model features

•Activity levels: none 62.8%low (1 partner per year)

15.5 %high (7.7 partners per year)

21.7 %

•Roles: MSM: heterosexuals:

versatile 50% insertive 50%

insertive 35% receptive 50%

receptive 15%

•Mixing by level: 16.6 times more likely to choose partners of the same activity level than expected by chance

UMHS

UMHS

NHSLS

Sources:

Model features

Transmissibility/ unprot. receptive anal 0.00500act: unprot. insertive anal 0.00065

unprot. receptive vaginal 0.00100unprot. insertive vaginal 0.00050

Acts/ 10 (for high-high)partnership: 50 (for high-low)

250 (for low-low)

•Size: small = 1,000; large = 10,000

•Removals: sero-ves: 30 years after entrysero+ves: 7.5 years after

seroconversion

•Arrivals: equal in number to removals

Vargheseet al. 1992

UMHS

Sources:

0

0.05

0.1

0.15

0.2

0.25

0 25 50 75 100 125 150

year

HIV

pre

va

len

ce

Results - HIV prevalence

MSM - all versatilesmall pop, anal transmissibility

0

0.05

0.1

0.15

0.2

0.25

0 25 50 75 100 125 150

year

HIV

pre

va

len

ce



Heterosexual or MSM-no versatilesmall pop, anal transmissibility

0

0.05

0.1

0.15

0.2

0.25

0 25 50 75 100 125 150

year

HIV

pre

va

len

ce



MSM – observed versatilitysmall pop, anal transmissibility


0

0.05

0.1

0.15

0.2

0.25

0 25 50 75 100 125 150

year

HIV

pre

va

len

ce




Heterosexuallarge pop, anal transmissibility


0

0.05

0.1

0.15

0.2

0.25

0 25 50 75 100 125 150

year

HIV

pre

va

len

ce

Results –HIV prevalence

Heterosexuallarge pop, vaginal transmissibility



Heterosexuallarge pop, anal transmissibility


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.)


If the partnering rates of the high-activity group are doubled:

Results (cont.)


If the partnering rates of the high-activity group are doubled:

0%

200%

400%

600%

800%

1000%

1200%

0 5 10 15 20

year

ch

an

ge

in H

IV p

rev

ale

nc

e

co

mp

are

d t

o o

bs

erv

ed

ac

tiv

ity

le

ve

ls

prevalence at year 20 of the epidemic is changed by

975% in MSM 170% in heterosexuals

MSM

Het

Implications

•Structural and biological factors can play major roles in increasing susceptibility of MSM populations to HIV.

Implications


•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



•MSM will remain relatively vulnerable to HIV/STD epidemics even with major shifts in behavior.

Implications




•What about Africa? higher infectivity other structural patterns not modeled herenosocomial

Implications




•What about Africa? higher infectivity other structural patterns not modeled herenosocomial

•More broadly, factors other than numbers of unsafe partners can predispose or protect different populations from STD epidemics.

Acknowledgments

University of Washington CFAR

King HolmesMartina MorrisMark Handcock

The entire staff of CAPS’ Urban Men’s Health Study

Joseph CataniaRon StallTom Coates

The participants in the Urban Men’s Health Study

Behavioral, Biological and Structural Components of MSM STI Morbidity Steven Goodreau and Matthew...

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