Statistics & Declining HCV infections

Mark Stoové, PhDCentre for Epidemiology & Population Health Research (CEPHR)Burnet Institute

Overview

• Basic epidemiology– Drug use and HCV

• The problem with incidence (for HCV surveillance)

• Enhanced HCV surveillance

• Modeling HCV incidence

• What these numbers tell us and where are we going?

Incidence & Prevalence?

Prevalence: refers to existing cases of diseaseIn 2005, 264,000 people living with HCV

antibodies.

Incidence: Rate at which new cases of disease enter the populationIn 2005, 9,700 new HCV infections.

HCV Incidence & Prevalence

Harm reduction

& prevention initiatives

Population at risk

HCV prevalence

HCV incidence

Mortality empties the pool

Tx & clearance

pumps people back up

HCV Incidence & Prevalence

Incidence & Prevalence?Both prevalence and incidence are affected

by testing rates & surveillance.

0

5000

10000

15000

20000

25000

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002

HCV Incidence?For incidence:

We can count the same person twice?

“The extent to which there have been duplicate HCV notifications is uncertain” (p.6)*

New HCV diagnoses notified with case identifying information thus limiting duplicate notifications, BUT this process still measures rate of diagnoses not infections …

* Hepatitis C Virus Projections Working Group, 2006

HCV Incidence?… we believe that the vast majority of HCV

notifications are prevalent HCV diagnoses.

HCV Incidence?Enhanced HCV surveillance introduced in

most States/Territories:1. Identified as new case (no previous +ve HCV

test)2. Notifying doctor contacted

• Reason for testing?• Acute symptoms in last 2 years?• Patient risk factors?

3. Testing laboratory contacted• Past serology results, LFTs etc

4. Patient contacted?5. Patient classified as newly acquired or

unknown

HCV Incidence?Patient Classification

1. Newly acquired (meets at ≥1 of the following)• detection of HCV antibody with previous negative HCV

antibody test in the past 24 months• detection of hepatitis C virus (nucleic acid testing) with

previous negative HCV antibody test in the past 24 months

• detection of HCV antibody from a child aged 18-24 months• detection of HCV antibody or RNA & clinical evidence

(jaundice/bilirubin in urine/ALT 7 normal)

2. Unspecified case (laboratory definitive evidence BUT none of above criteria)

HCV Incidence?But problems remain:

• detection of HCV antibody / virus and previous negative tests

Negative HCV test results cannot be cross-checked b/w different testing laboratories

• detection of HCV antibody or RNA & clinical evidence (jaundice/bilirubin in urine/ALT 7 normal)

Perhaps as few as 10% of HCV infections are associated with acute symptoms*

* Van der Poel et al., 1994

HCV Incidence?

HCV Incidence?Combined with:• irregular testing of people at risk of HCV

infection• large resources required to do enhanced

surveillance• Privacy concerns, anonymity, confidentiality

Only a small number of recent infections can be detected.Fewer than 300 cases/year between 2002 & 2005.

HCV Incidence?

So how do we determine HCV incidence (& prevalence)?

We take a thoughtful and very well informed

GUESS.

Measuring HCV Incidence

≈ 80% of HCV prevalence cases & 90% of HCV incidence cases contracted through risky IDU.– Remainder - migration (country of origin),

unsafe tattooing, contaminated blood products, mother-child transmission.

Therefore, estimates of HCV incidence rely heavily measuring parameters associated with IDU.

HCV Incidence?What is the size of the high-risk (IDU) population?

… and what is the likelihood that they will become infected with HCV?

Measuring HCV Incidence

We need to know:– The number of IDU

• Changes over time?• Frequency of injection (regular, occasional)• Confounded by other things such as risk behaviour,

drug injected, incarceration etc.

– The risk of contracting HCV among IDU

Number of IDU?Heroin overdose deaths

Opioid overdose deaths

1116

938

386 364 357

0

200

400

600

800

1000

1200

1999 2000 2001 2002 2003

Ye

ar

Opioid overdosedeaths

Number of IDU?Opiate-related hospitalisations

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1999 2000 2001 2002 2003 2004

Heroin

Other opioids

Methadone

Number of IDU?Drug-related arrests

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

1997-1998

1998-1999

1999-2000

2000-2001

2001-2002

2002-2003

2003-2004

Heroin and other opioids

Amphetamine-typestimulants

Cocaine

Number of IDU?NSP attendances (by drug last injected)

0

500

1,000

1,500

2,000

2,500

3,000

1998 1999 2000 2001 2002 2003 2004

Heroin

Amphetamine

Total

Number of IDU?NSP attendances, Victoria 2000-2005

6,753,1836,175,861

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

2000 2001 2002 2003 2004 2005

NSP distribution in VIC

Number of IDU?HCV notifications among 15-24 year olds

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

1998 1999 2000 2001 2002 2003 2004

Number of IDU?NDSHS results (injected last 12 months)

110,000

91,000

74,000

0

20,000

40,000

60,000

80,000

100,000

120,000

1998 2001 2004

Number of IDU?NDSHS results (injected last 12 months)

110000

91000

74000

5650 46

0

20000

40000

60000

80000

100000

120000

1998 2001 2004

# o

f ID

U

0

10

20

30

40

50

60

70

80

90

100

% r

epo

nse

rat

e

estimate # of IDU

response rate

Number of IDU?

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

1970 1975 1980 1985 1990 1995 2000 2005

Year

Nu

mb

er

of

reg

ula

r ID

Us

Average

NSP

Arrests

NDSHS

HCV

OD/Hosp/Amb

Estimated # of regular IDUs

Number of IDU?

2000 2001 2002 2003 2004 2005% change in IDU

0 18 10 2 3 1

% stopped injecting

10 25 16 7 7 5

% started injecting

10 7 6 5 4 4

Declines in IDU between 2000 and 2005 assumed:

Number of IDU?

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

1970 1975 1980 1985 1990 1995 2000 2005

year

Nu

mb

er

of

IDU

s

Occasional IDUs Regular IDUs

Number of IDU?

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

1970 1975 1980 1985 1990 1995 2000 2005

year

Nu

mb

er

of

IDU

s

Occasional IDUs Regular IDUs

Number of IDU?

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

1970 1975 1980 1985 1990 1995 2000 2005

year

Nu

mb

er

of

IDU

s

Occasional IDUs Regular IDUs

HCV Incidence?What is the size of the high-risk (IDU) population?

… and what is the likelihood that they will become infected with HCV?

Incidence of HCV Among IDUEstimating the incidence of HCV among IDU

assumed:1. HCV incidence among regular IDUs as 18% per

annum between 1960 and 1985 after which incidence declined to 13% thereafter.

2. Incidence among occasional IDUs is 20% of that in regular IDUs.

Based on 1 cohort study in Melbourne (Crofts et al, 1997) and 1 in Sydney (van Beek et al 1998)

More recent cohort studies have shown incidence closer to 30%??

Other Modelling?

• Migrants from countries of high (>2%) HCV prevalence.– Census data for # migrants from these

countries (almost 1 million by 2005).– Country-specific HCV prevalence (assuming

migration is independent of HCV status)

• Mortality (population and current & former IDU)

Other Modelling?• Mother-child transmission

0

20

40

60

80

100

120

140

160

180

200

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

year

Est

aim

ated

# m

oth

er-c

hil

d H

CV

tr

ansm

issi

on

s

Incidence of HCV?

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

year

Num

ber o

f inf

ectio

ns

Migrants IDUs Others

2005 •incidence = 9,700

Incidence of HCV?

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

year

Num

ber o

f inf

ectio

ns

Migrants IDUs Others

2005 •incidence = 9,700

– IDU = 8,600 (89%)

Incidence of HCV?

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

year

Num

ber o

f inf

ectio

ns

Migrants IDUs Others

2005 •incidence = 9,700

– IDU = 8,600 (89%)

– Migrants = 700 (7.2%)

Incidence of HCV?

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

year

Num

ber o

f inf

ectio

ns

Migrants IDUs Others

2005 •incidence = 9,700

– IDU = 8,600 (89%)

– Migrants = 700 (7.2%)

– Blood products / other routes = 400 (4.1%)

Incidence of HCV?2005 incidence = 9,700 compared to 2001 incidence = 16,000

BUT… if we use updated estimates used from 2005 … 2001 incidence = 11,000

Incidence of HCV?

* Hepatitis C Virus Projections Working Group, 2006, p 25-26

What do these numbers tell us?

1. It is extremely hard to accurately estimate the size of the major population at risk.

a) Dynamic and temporal changes complex

2. Because cohort studies are infrequently conducted in Australia, estimates of risk of infection are few.

3. It is, therefore, extremely hard to accurately estimate the incidence of HCV.

4. Recent estimates of a reduction in HCV incidence is based almost entirely on the declining estimate of the number of IDU in Australia.

If the numbers are going down, who is going to take

the credit?1. Everyone2. Christopher Pine3. Australian Federal Police 4. Drug cultivation and manufacturing syndicates in

Asia5. HCV & IDU community groups6. HCV & IDU educators7. NSPs8. Users themselves

What about future transmissions, will they keep

coming down?

Based on current methods this completely depends on estimates associated with the number of IDU

This assumes that the risk environment stays static??

Open the flood gates on HCV