serial monogamy and the spread of hiv

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Serial monogamy and the spread of HIV. How explosive can it get? Wim Delva MD, PhD Carel Pretorius MSc, PhD Stijn Vansteelandt MSc, PhD Marleen Temmerman MD, PhD Brian Williams MSc, PhD. 3. Serial monogamy and the spread of HIV. Department of Health , South Africa , 2009. - PowerPoint PPT Presentation

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Serial monogamy and the spread of HIV

How explosive can it get?

Wim Delva MD, PhDCarel Pretorius MSc, PhDStijn Vansteelandt MSc, PhDMarleen Temmerman MD, PhDBrian Williams MSc, PhD

3. Serial monogamy and the spread of HIV

Department of Health, South Africa, 200926

2

The compartmental model

R10C

R10L

Sero-discordant casual relationship

Sero-discordant long-term relationship

27

3

R10C

R10L R11

L

R11Cν(τ)

ν(τ)Sero-concordant casual relationship

Sero-concordant long-term relationship

The compartmental model

27

ν = HIV transmission rateτ = times since infection 4

R10C

R10L R11

L

R11Cν(τ)

ν(τ)

f CσC

f LσL

σ = partner turnover ratef = assortativeness parameter

The compartmental model

27

5

R10C

R10L R11

L

R11Cν(τ)

ν(τ)

f CσC

f LσL

(1-f C)σC

(1-f

L)σL

σ = partner turnover ratef = assortativeness parameter

The compartmental model

27

6

R10C

R10L R11

L

R11Cν(τ)

ν(τ)

f CσC

f LσL

(1-f C)σC

(1-f

L)σL

(1-f C)σC (1-f

L)σL

The compartmental model

27

σ = partner turnover ratef = assortativeness parameter 7

μ(τ) μ(τ)

μ(τ)μ(τ)R10

C

R10L R11

L

R11Cν(τ)

ν(τ)

f CσC

f LσL

(1-f C)σC

(1-f

L)σL

(1-f C)σC (1-f

L)σL

μ = HIV-related mortality rate

The compartmental model

27

8

Parameter Base-case value (Peak)

Range

Transmission probability per sex act

Acute 0.92% 0.28%-3.60%

Chronic 0.10% 0.05%-0.20%

Late 0.73% 0.20%-1.53%

Co-factor effect of other STIs

Relative risk of HIV transmission 4 2-9

STI prevalence in casual relationships 50% 20%-80%

STI prevalence in long-term relationships 20% 10%-50%

Frequency of sex acts 2 / week 1-3

Average duration of relationships

Casual relationships 3 months 26 days-6 months

Long-term relationships 1 year 6 months-2 years

Fraction of relationships that are casual 30% 10%-50%

Uncertainty analysis

28

9

Results

Doubling time (years)

Frac

tion

of s

imul

atio

ns

29

10

R0

Doubling time (years)

Frac

tion

of R

0 in

1st y

ear

Base case

Results

30

11

Sensitivity analysis

31

12

How to get a DT of 1.2 years?

31

13

Variable ValueSTI cofactor 20.2Frequency of sex 7.6 sex acts / weekPSTP Acute / (DT > 1.9 years) Chronic 0.55% Late 40%Fraction casual / (DT > 2.0 years)Partner turnover rate 2 / weekSTI prevalence In casual relations / (DT > 2.4 years) In long-term relations / (DT > 2.1 years)

Conclusions Serial monogamy unlikely to result in doubling

time of 1.2 years or less

The South African HIV epidemic is unlikely to have emerged from a serially monogamous sexual network

Serial monogamy reduces effect of high acute infectiousness

New models needed to capture the effect of concurrency realistically

Other potential (partial) explanations: Anal sex, MSMW, unsafe medical injections

32

14

50

Thanks

15

IWT (Flemish Institute for Innovation through Science and Technology)

FWO (Flemish Research Fund)

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