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
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