Statistics

1
Statistics Declining HCV infections

• Mark Stoové, PhD
• Centre for Epidemiology Population Health
  Research (CEPHR)
• Burnet Institute

2
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?

3
Incidence Prevalence?
Prevalence refers to existing cases of
disease In 2005, 264,000 people living with HCV
antibodies. Incidence Rate at which new cases
of disease enter the population In 2005, 9,700
new HCV infections.
4
HCV Incidence Prevalence
Tx clearance pumps people back up
Population at risk
Harm reduction prevention initiatives
Mortality empties the pool
HCV prevalence
HCV incidence
5
HCV Incidence Prevalence
6
Incidence Prevalence?
Both prevalence and incidence are affected by
testing rates surveillance.
7
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
8
HCV Incidence?
we believe that the vast majority of HCV
notifications are prevalent HCV diagnoses.
9
HCV Incidence?

• Enhanced HCV surveillance introduced in most
  States/Territories
• Identified as new case (no previous ve HCV test)
• Notifying doctor contacted
• Reason for testing?
• Acute symptoms in last 2 years?
• Patient risk factors?
• Testing laboratory contacted
• Past serology results, LFTs etc
• Patient contacted?
• Patient classified as newly acquired or unknown

10
HCV Incidence?

• Patient Classification
• 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)
• Unspecified case (laboratory definitive evidence
  BUT none of above criteria)

11
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

12
HCV Incidence?
13
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.

14
HCV Incidence?
So how do we determine HCV incidence (
prevalence)? We take a thoughtful and very
well informed GUESS.
15
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.

16
HCV Incidence?
and what is the likelihood that they will
become infected with HCV?
What is the size of the high-risk (IDU)
population?
17
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

18
Number of IDU?
Heroin overdose deaths
19
Number of IDU?
Opiate-related hospitalisations
20
Number of IDU?
Drug-related arrests
21
Number of IDU?
NSP attendances (by drug last injected)
22
Number of IDU?
NSP attendances, Victoria 2000-2005
23
Number of IDU?
HCV notifications among 15-24 year olds
24
Number of IDU?
NDSHS results (injected last 12 months)
25
Number of IDU?
NDSHS results (injected last 12 months)
26
Number of IDU?
Estimated of regular IDUs
27
Number of IDU?
Declines in IDU between 2000 and 2005 assumed
28
Number of IDU?
29
Number of IDU?
30
Number of IDU?
31
HCV Incidence?
and what is the likelihood that they will
become infected with HCV?
What is the size of the high-risk (IDU)
population?
32
Incidence of HCV Among IDU

• Estimating the incidence of HCV among IDU
  assumed
• HCV incidence among regular IDUs as 18 per annum
  between 1960 and 1985 after which incidence
  declined to 13 thereafter.
• 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??

33
Other Modelling?

• Migrants from countries of high (gt2) 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)

34
Other Modelling?

• Mother-child transmission

35
Incidence of HCV?

• 2005
• incidence 9,700

36
Incidence of HCV?

• 2005
• incidence 9,700
• IDU 8,600 (89)

37
Incidence of HCV?

• 2005
• incidence 9,700
• IDU 8,600 (89)
• Migrants 700 (7.2)

38
Incidence of HCV?

• 2005
• incidence 9,700
• IDU 8,600 (89)
• Migrants 700 (7.2)
• Blood products / other routes 400 (4.1)

39
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
40
Incidence of HCV?
Hepatitis C Virus Projections Working Group,
2006, p 25-26
41
What do these numbers tell us?

• It is extremely hard to accurately estimate the
  size of the major population at risk.
• Dynamic and temporal changes complex
• Because cohort studies are infrequently conducted
  in Australia, estimates of risk of infection are
  few.
• It is, therefore, extremely hard to accurately
  estimate the incidence of HCV.
• Recent estimates of a reduction in HCV incidence
  is based almost entirely on the declining
  estimate of the number of IDU in Australia.

42
If the numbers are going down, who is going to
take the credit?

• Everyone
• Christopher Pine
• Australian Federal Police
• Drug cultivation and manufacturing syndicates in
  Asia
• HCV IDU community groups
• HCV IDU educators
• NSPs
• Users themselves

43
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??
44
Open the flood gates on HCV