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Ingrid van Beek a Kirketon Road Centre, PO Box 22, Kings Cross, New
South Wales 1340, Australia, b National
Centre in HIV Epidemiology and Clinical Research, University of New
South Wales, Sydney, Australia
Correspondence to: Dr van Beek ivanbeek{at}ozemail.com.au
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Abstract |
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Objectives: To estimate the incidence of HIV and
hepatitis C virus and risk factors for seroconversion among a cohort of
injecting drug users.
Design: Retrospective cohort study.
Setting: Primary healthcare facility in central
Sydney.
Subjects: Injecting drug users tested for HIV-1
antibody (n=1179) and antibodies to hepatitis C virus (n=1078) from February 1992 to October 1995.
Main outcome measures: Incidence of HIV-1 and
hepatitis C virus among seronegative subjects who injected drugs and underwent repeat testing. Demographic and behavioural risk factors for
hepatitis seroconversion.
Results: Incidence of HIV-1 among 426 initially
seronegative injecting drug users was 0.17/100 person years (two
seroconversions) compared with an incidence of hepatitis C virus of
20.9/100 person years (31 seroconversions) among 152 injecting drug
users initially negative for hepatitis C virus. Incidence of hepatitis
C virus among injecting drug users aged less than 20 years was 75.6/100 person years. Independent risk factors for hepatitis C virus
seroconversion were age less than 20 years and a history of
imprisonment.
Conclusions: In a setting where prevention measures
have contributed to the maintenance of low prevalence and incidence of
HIV-1, transmission of hepatitis C virus continues at extremely high
levels, particularly among young injecting drug users.
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Key messages
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Introduction |
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Several studies have documented high prevalence of infection with hepatitis C virus among injecting drug users, both in industrialised1-9 and developing countries.10-12 Although longer duration of drug use has been consistently associated with higher prevalence of hepatitis C virus infection among this population, 1 3 5 12-16 high prevalence has also been reported among both young injecting drug users 3 17 and those who have been injecting for a relatively short time.18 Studies of hepatitis C virus incidence have found high levels of transmission among current injecting drug users 1 5 19-23 and prison inmates, 5 24 but these studies have been based on relatively few seroconversions (1-10), limiting their potential to identify risk factors for newly acquired hepatitis C virus infection.
In Australia the extensive and continuing spread of infection with hepatitis C virus among injecting drug users has occurred in an environment where prevention strategies, including the wide implementation of needle and syringe exchange programmes since 1987, have contributed to the maintenance of a low prevalence (1-3%) and incidence of HIV. 1 3 5 25-27 We undertook a study of incidence of hepatitis C virus among injecting drug users attending Kirketon Road Centre, Sydney, with the major objective of identifying risk factors for newly acquired infection.
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Methods |
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Kirketon Road Centre is a government funded facility in central Sydney established in 1987 to prevent and treat HIV/AIDS and other transmissible infections in young people, sex workers, and injecting drug users.28
In December 1991 testing for antibodies to hepatitis C virus became available in the context of clinical care at the centre, in addition to the existing provision of HIV screening. Hepatitis C virus testing was offered to all clients who reported a history of injecting drug use. All injecting drug users who underwent testing at the centre from February 1992 to October 1995 were included in the present study.
Standard HIV antibody testing was performed, including initial HIV enzyme linked immunosorbent assay (ELISA) with confirmatory western blot testing. Hepatitis C virus antibody testing was by the Monolisa R (ELISA) test, a second generation ELISA (Sanofi Diagnostics, Pasteur). All specimens positive for hepatitis C virus antibody underwent repeat testing. Only those who tested positive on second generation repeat testing were considered positive.
Information on demographic characteristics, sexual practice, and history of drug injecting were obtained from the client's medical file at the centre. This information was recorded by the clinical practitioner for all clients at the first visit and at the time of testing for HIV or hepatitis C virus. All behavioural information recorded at the first clinic visit referred to risk behaviour in the previous 12 months. Information recorded at the time of repeat testing for HIV or hepatitis C virus referred to risk behaviour in the previous 12 months or since risk behaviour was last documented in the client's medical file (that is, since the first clinic visit or since the previous test visit), whichever was shorter. Periods of non-use between the age when clients started injecting and current age were subtracted in the estimation of duration of injecting drug use.
Analysis
Two separate statistical analyses were carried out. Incidence of
HIV and hepatitis C virus infection was calculated by using the person
years method29 among clients initially seronegative for
HIV antibody and hepatitis C virus antibody, respectively, who
underwent repeat testing within the study period. Date of seroconversion was taken as the midpoint between the last negative and
first positive antibody tests.
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Results |
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Incidence of HIV-1
During the study period, HIV-1 antibody testing was carried out on
1179 clients who gave a history of injecting drug use. The overall
prevalence of infection was 2.5%.
Incidence of hepatitis C virus
During the same period hepatitis C virus antibody testing was
carried out on 1078 clients. The overall prevalence of infection was
45%.
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Discussion |
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We have shown an extremely high risk of hepatitis C virus infection among injecting drug users with continuing low prevalence and incidence of HIV infection who attend a primary healthcare service focused on the prevention of bloodborne infections. The risk of newly acquired hepatitis C virus infection was greatest among clients aged less than 20 years and those with a history of imprisonment. This study seems to be the largest so far carried out in terms of the number of recorded hepatitis C virus seroconversions and is consistent with previous reports from Australia, 1 5 Switzerland,19 and Germany21 in identifying a continuing high incidence of hepatitis C virus coincident with low incidence of HIV in injecting drug users.
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Limitations of study
Several methodological issues need to be considered in the
interpretation of these results. Although this study is the largest of
incident hepatitis C virus cases reported in the literature to date,
only 31 incident cases were observed, limiting the power of the
analyses and the extent to which confounding can be excluded as an
explanation of the observed associations. Despite this, our study had
about 70% power (0.05% level) to detect a halving in incidence over
the study period.
but if all those who had an initial test had undergone
repeat testing the association between imprisonment and newly acquired
hepatitis C virus infection should have persisted.
Another methodological limitation is the dependence on self reports for
information on injecting practice, particularly in a clinical context
where the client may perceive an incentive to underreport risk
behaviour to the attending clinician. Misclassification of variables
has the effect of reducing the apparent size of any association,
provided the extent of misclassification was not associated with
hepatitis C virus status or the true values of the variables. There is
no way to assess this issue on the basis of available data.
Incidence of hepatitis C
The extremely high incidence of hepatitis C virus among subjects
under 20 years (76 per 100 person years) is a major public health
concern. Younger injecting drug users could be at relatively higher
risk of seroconversion compared with seronegative older injecting drug
users if seronegativity becomes a marker of well established prevention
practices with increasing duration of injection and age. Thus,
increasingly lower risk cohorts of injecting drug users may be
established with increasing age as those at higher risk are removed
because of hepatitis C virus seroconversion. The 84% of injecting drug
users under 20 years old who were negative for hepatitis C virus on
initial testing presumably contains a higher proportion of high risk
injecting drug users than the 26% of injecting drug users over 30 years old who were initially negative for hepatitis C virus. While
prevalence studies indicate the cumulative impact of hepatitis C virus
infection, only incidence studies can identify where infection is
currently occurring and allow the direct assessment of the
effectiveness of current prevention strategies.
for example, the sharing of items such as razors
and toothbrushes, which may draw blood.
An important finding from the study was the strong relation between a
history of imprisonment and the incidence of hepatitis C virus. We
could not determine on the basis of available data whether the period
of imprisonment was between the last negative and first positive test
result in subjects who acquired hepatitis C virus infection. The
observed association may be due to risk behaviour in prison or a
consequence of an association between history of imprisonment and
chaotic lifestyle, which may in turn be a surrogate marker of injecting
risk behaviour. In either case, the association observed in this study
population deserves further investigation, specifically to assess
whether preventing the spread of hepatitis C virus should be better
dealt with in the prison setting.
A recently published prospective cohort study among injecting drug
users in another Australian state revealed a decline in incidence of
hepatitis C virus, albeit non-significant, of 16.6 to 8.1/100 person
years over the period 1990-5.31 The absence of a similar
decline in this study among an inner city population of injecting drug
users already attending an HIV prevention service strongly suggests
that current efforts aimed at the prevention of bloodborne viral
transmission are inadequate to stem hepatitis C virus infection. The
vulnerability of this population to hepatitis C virus may ultimately
indicate the potential for HIV transmission.
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Acknowledgments |
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Contributors: IB, chief investigator and guarantor of the study, initiated and coordinated the formulation of the primary study hypothesis and design of questionnaires, and participated in interpreting findings and writing the paper. RD participated in formulating the primary study hypothesis and designing questionnaires, coordinated data analysis and interpretation, and edited the paper. GJD participated in interpreting findings and writing the paper. KL participated in data analysis and interpretation. JMK participated in formulating the primary study hypothesis, designing questionnaires, and interpreting findings, and edited the paper.
Funding: The National Centre in HIV Epidemiology and Clinical Research is supported by the Commonwealth Department of Health and Family Services through the Australian National Council on AIDS and Related Diseases and its research advisory committee.
Conflict of interest: None.
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References |
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(Accepted 5 May 1998)
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