Modelling HIV/AIDS in Southern Africa

Centre for Actuarial Research (CARe)A Research Unit of the University of Cape Town

History of the ASSA AIDS and Demographic model Doyle-Metropolitan model (c1990) ASSA500 (c1995) ASSA600 (c1998) ASSA2000 suite (2001): lite, full, provincial

(beta 2002) ASSA2002 lite and full (2004) ASSA2003 suite (2005): lite, full, provincial Other models (www.assa.org.za/aidsmodel.asp)

Orphans, select populations, other countries

Methodology: ASSA model

Antenatal data(by age)

Adult death data

Adjust for bias (public anc vs all

women)

Demographic parameters (base population, fertility, non-

AIDS mortality and migration)Cohort component projection model

Calibration

Epi and behavioural parameters(e.g. % in risk groups, amount of sex,

probability of transmission, probability a condom used, etc)

Epidemiological, behavioural,

intervention model

Interventions (IEC, VCT, STI, PMTCT, ART)

Detailed output including:No. infectedNo. new infectionsNo. AIDS deaths, etc

Features of the ASSA lite model

Heterosexual behavioural cohort component projection model (individual ages/years)

Population divided by risk by: Age (young, adult, old) ‘Behaviour’ (PRO, STD, RSK, NOT) ‘Previous socio-economic disadvantage’ (racial groups) Geographic region (province)

Sex activity Risk group of partner, probability of transmission, number

of new partners p.a., number of contacts per partner, condom usage,

No sex between racial groups or provinces

Diagram 1: A schematic diagram of the ASSA600 Aids Model

Adu

lt (1

4 -

59)

Old

(60+

)

HIV- Young HIV+ Young

NOT RSK STD PRO

Increasing sexual mobility

Increasing risk of HIV infection

HIV- Old HIV+ Old

Dea

ths

Normal Deaths AIDS Deaths

Imported HIV

Migrants (0-59)

Migrants (Aged 60+)

HIV- Births HIV+ Births

You

ng (0

-

13)

Modelling prevention and treatment

Five interventions: Social marketing, information and

education campaigns (IEC) Improved treatment for sexually

transmitted diseases (STDs) Voluntary counselling and testing (VCT) Prevention of mother-to-child

transmission (PMTCT) Antiretroviral treatment (ART)

The fitting process - calibration

Set as many of the parameters/assumptions from independent estimates (% STD, probability of transmission, condom usage, age of (male) partners, the median term to survival of adults and children, impact of HIV on fertility and bias in ANC data, all non-HIV demographic assumptions)

Set some other assumptions (which are not particularly important) by reasonable guesses (e.g. relative fertility, and risk groups of migrants)

The remaining assumptions are set in order to produce known data of the prevalence or impact of the epidemic such as the antenatal prevalence and the mortality figures - calibration (e.g. size of the RSK group, the mixing of risk groups, sex activity by age, no. of partners, number of contacts per partner)

Calibration targets

Prevalence levels Antenatal – overall prevalence Antenatal – prevalence by age over time Ratio of antenatal to national by age HSRC prevalence by sex and age

Deaths Population or vital registration – overall by sex, age

and over time Cause of Death – proportion AIDS in adults by sex

and age Cause of Death – proportion AIDS in children by age Cause of Death – ratio of male to female by age over

time

Calibration targets(cont’d)

Census Numbers by sex and age nationally and provincially Mortality rates by age and sex

Orphanhood CEB/CS Deaths in household

Other Numbers on treatment (private and public)

Antenatal prevalence: South Africa

Confidence intervals prior to 1998 were incorrectly calculated – should be wider

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%1

99

0

19

92

19

94

19

96

19

98

20

00

20

02

20

04

20

06

20

08

20

10

Pe

rce

nta

ge

Model

anc prevalence

adjusted for bias

Number of deaths - men

0

5000

10000

15000

20000

25000

30000

35000

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85+

Proj2002

1996

1997

1998

1999

2000

2001

2002

Number of deaths - women

0

5000

10000

15000

20000

25000

30000

35000

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85+

Proj2002

1996

1997

1998

1999

2000

2001

2002

Uncertainty

Demography (Base population, Fertility, Mortality & Migration)

Epidemiological assumptions (% in risk groups, mixing of the risk groups, probabilities of transmission, infectivity and infectiousness by stage, etc)

Interventions (in particular treatment) Roll-out Effectiveness

Behaviour Future developments (e.g. vaccine)

Selected results

Comparison with HSRC05: South Africa (Prevalence: males and females)

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

2-14

15-1

9

20-2

4

25-2

9

30-3

4

35-3

9

40-4

4

45-4

9

50-5

4

55-5

9

60+

ASSA2003

HSRC05

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

30.0%

35.0%

40.0%

2-1

4

15

-19

20

-24

25

-29

30

-34

35

-39

40

-44

45

-49

50

-54

55

-59

60

+ASSA2003

HSRC05

Prevalence: adults 20-64: South Africa

0%

5%

10%

15%

20%

25%

30%

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

2011

2013

2015

EasternCapeFree State

Gauteng

KwaZulu-NatalLimpopo

Mpumalanga

NorthernCapeNorth West

WesternCapeSouth Africa

Numbers infected by province: South Africa

0.00

1.00

2.00

3.00

4.00

5.00

6.00

1985

1987

1989

1991

1993

1995

1997

1999

2001

2003

2005

2007

2009

2011

2013

2015

Mil

lio

ns

Western Cape

North West

Northern Cape

Mpumalanga

Limpopo

KwaZulu-Natal

Gauteng

Free State

Eastern Cape

Numbers on HAART by province: South Africa

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,0002

00

0

20

02

20

04

20

06

20

08

20

10

20

12

20

14

Western Cape

North West

Northern Cape

Mpumalanga

Limpopo

KwaZulu-Natal

Gauteng

Free State

Eastern Cape

Prevalence 15-49 by sub-district: Botswana

0%

5%

10%

15%

20%

25%

30%

35%

40%

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

Barolong Bobonong C.Kgalagadi.G.R Central-Boteti Chobe Francistown

Gaborone Ghanzi Jwaneng Kgalagadi-North Kgalagadi-South Kgatleng

Kweneng-East Kweneng-West Lobatse Mahalapye Ngamiland-Delta Ngamiland-East

Ngamiland-West Ngwaketse-West North-East Orapa Selebi-Phikwe Serowe-Palapye

South-East Southern Sowa-Pan Tutme Sum NATIONAL

Numbers infected by stage by year: Botswana

0

50 000

100 000

150 000

200 000

250 000

300 000

350 000

400 00019

80

1984

1988

1992

1996

2000

2004

2008

2012

2016

2020

AIDS-off ART

ART

AIDS-pre ART

Pre-AIDS

Numbers of deaths by year: Botswana

0

5 000

10 000

15 000

20 000

25 000

30 000

35 000

1981

1984

1987

1990

1993

1996

1999

2002

2005

2008

2011

2014

2017

2020

AIDS

Non-AIDS

Future developments

Circumcision Vaccine Age-specific interventions Pregnancy and transmission? Risk group migration? Better demographic estimation Uncertainty Education? Household impact? Fitting to other (SADC) countries