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Statistics & Declining HCV infections Mark Stoové, PhD Centre for Epidemiology & Population Health Research (CEPHR) Burnet Institute.

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Presentation on theme: "Statistics & Declining HCV infections Mark Stoové, PhD Centre for Epidemiology & Population Health Research (CEPHR) Burnet Institute."— Presentation transcript:

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 Harm reduction & prevention initiatives Population at risk HCV prevalence HCV incidence Mortality empties the pool Tx & clearance pumps people back up

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: 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

10 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 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)

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

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

23 Number of IDU? HCV notifications among 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? % change in IDU % stopped injecting % started injecting Declines in IDU between 2000 and 2005 assumed:

28 Number of IDU?

29

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

32 Incidence of HCV Among IDU Estimating 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%??

33 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)

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? 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.

42 If the numbers are going down, who is going to take the credit? 1.Everyone 2.Christopher Pine 3.Australian Federal Police 4.Drug cultivation and manufacturing syndicates in Asia 5.HCV & IDU community groups 6.HCV & IDU educators 7.NSPs 8.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


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