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HAMILTON, Ontario, CANADA L8N 4A6
PHONE: (905) 521-6141
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http://www.fhs.mcmaster.ca/hrlmp/
Issue No. 66
QUARTERLY NEWSLETTER
December 2002
Viral Hepatitis C Testing Update
The global prevalence of HCV infection is approximately 3% with 170 million people infected while in
North America about 1.8% of the population is infected (1). The primary mode of transmission is exposure
to infected blood via intravenous drug use or unscreened transfusions. Screening blood donors has
dramatically reduced the incidence of post-transfusion acquired hepatitis, the risk is currently about 1 in 3
million in Canada(2). Nosocomial HCV transmission during dialysis, colonoscopy and surgery has been
reported and the rate of seroconversion in health care workers after a needlestick is in the range from 0 to
7% (3). Perinatal and sexual transmission is inefficient (1 to 3%) with the former occurring more frequently
in individuals with an HIV infection (3). Most people with an acute HCV infection are asymptomatic or
have mild symptoms (fatigue, nausea, jaundice) but are unable to clear the virus and are chronically
infected in about 80% of cases (1). Chronic infections progress to cirrhosis in 20 to 30% of patients and
there is also a 1 to 4% annual risk of developing hepatocellular carcinoma (1). Although screening the
general population is not recommended, donors and individuals at risk should be tested. Detailed
recommendations for identifying infected individuals have been published (3).
Antibody Tests
While HCV cannot be detected in cell culture, a number of serological tests have been developed for antiHCV antibody and viral RNA (4). The viral genome codes for both structural (C,E1,E2) and non-structural
(NS1-NS5) proteins. The initial screening test used to diagnose HCV is an enzyme immunoassay (EIA).
These tests have evolved from first generation tests introduced in 1992 to third generation (EIA 3.0)
assays currently in use. Despite their improved sensitivity with more rapid detection of antibody, the
screening EIAs continue to produce false positive results that must be confirmed by supplemental or
confirmatory tests. The recombinant immunoblotting assay (RIBA) was first introduced in 1992 and it also
has been replaced by a third generation test (RIBA III). A similar confirmatory test called INNOLIA Update
(from Innogenetics) is currently in use by the Toronto Public Health Laboratory. These confirmatory tests
are considered positive if there are reactions with at least two antigens and indeterminate if only one
antibody band appears. Serological assays that detect HCV antibodies indicate present or previous
infection but are not able to discriminate acute from chronic or resolved infections. Just over half of the
patients with acute infections who develop symptoms will have detectable antibody at that time, while up
to 90% will have antibody after 3 months (5). Anti-HCV IgM antibody tests are not a reliable indicator of
infection and are not in widespread use (4).
HCV RNA Tests
The presence of HCV RNA in plasma defines active infection and RNA can be detected 1 to 3 weeks
post-exposure (5). RNA is detected using commercially available nucleic acid detection tests that are
either qualitative or quantitative. These include a qualitative (AMPLICOR HCV ver. 2.0) and quantitative
PCR
(AMPLICOR HCV MONITOR ver. 2.0) from Roche Diagnostics, a quantitative branched DNA test
(VERSANT HCV RNA ver. 3.0) from Bayer Diagnostics and a newer transcription mediated amplification
(TMA-VERSANT HCV RNA) qualitative test from Bayer Diagnostics. These commercial assays no longer
report numbers of copies of RNA per milliliter, but instead report international units per milliliter (IU/mL)
introduced recently by the World Health Organization to allow comparison between results achieved with
different assays (6). The qualitative AMPLICOR HCV test (ver. 2.0) has a detection limit of 50 IU/mL and
the quantitative assay a detection limit of 500 IU/mL. The Toronto PHL uses both the AMPLICOR HCV
qualitative and AMPLICOR HCV MONITOR quantitative tests. Qualitative RNA tests are used to establish
infection/infectivity, to confirm EIA screening or RIBA indeterminate results, to confirm infection in
immunocompromised patients that fail to seroconvert, and to confirm infection in a newborn that has
passively-acquired maternal HCV antibody. A single negative RNA test should be interpreted with caution
and cannot exclude infection as some individuals have low levels of viremia that can oscillate below the
level of detection of a given assay. Quantitative tests are used to establish baseline pre-treatment levels
of virus and to monitor response in individuals treated with antiviral drugs. Requests for viral load and
genotyping tests are only performed when accompanied by clinical information viz. either pre-treatment
(baseline) or elevated liver enzymes.
HCV Genotyping
HCV has been divided into 6 major genotypes and over 80 subtypes. Commercial genotyping tests
involve hybridization or sequencing methods to assign a genotype. The widely used INNO-LiPA HCV II
ver. 2.0 test (Innogenetics) currently used by the PHL uses PCR products obtained by the Roche
AMPLICOR for hybridization with genotype-specific probes immobilized on nitrocellulose strips. The
INNO-LiPA HCV II genotyping test reports 6 types and 21 subtypes. HCV genotyping is used primarily in
management decisions regarding treatment. Treatment for chronic HCV infection has progressed from
monotherapy with interferon which gave disappointing sustained virologic response (SVR) rates of only
10-20% (5), to combination therapy with interferon plus ribavirin, which is associated with a higher SVR
rate of nearly 40%. Optimal therapy is now considered to be a combination of pegylated interferon plus
ribavirin, with reported SVRs of 56%. Successful treatment has been associated with low viral load at
baseline, infection with a non-type 1 genotype, absence of cirrhosis, age less than 40 years and female
gender (7). Although the incidence of new cases of HCV infections in North America is declining, the
population of individuals infected for >20 years who are at risk for serious complications is projected to
increase until about 2015. As new therapeutic options emerge and laboratory assays continue to evolve,
the clinical relevance and use of laboratory tests for HCV will require frequent reassessments.
James B. Mahony, Ph.D., F.A.A.M., F.C.C.M.
Head, Regional Virology and Chlamydiology Laboratory
St. Joseph's Healthcare
References:
1. Lauer, G.M., and B.D. Walker. (2001). Hepatitis C virus infection. N. Engl. J. Med. 345:41-52.
2. Kleinman, S. (2003). Transfusion Medicine Reviews. 17 (2), in press.
3. Centers for Disease Control and Prevention. (1998). Recommendations for prevention and
control of hepatitis C virus (HCV) infection and HCV-related chronic disease. Morb. Mortal. Wkly.
Rep. 47 (RR-19):1-39.
4. Richter, S.S. (2002). Laboratory assays for diagnosis and management of Hepatitis C virus
infection. J. Clin. Microbiol. 40:4407-4412.
5. National Institutes of Health Consensus Development Conference Panel. (1997). Management of
hepatitis C. Hepatology 26 (Suppl.1):2S-10S.
6. Pawlotsky, J.-M. et al. (2000). Standardization of hepatitis C RNA quantification. Hepatology
32:654-659
7. Zein, N.N. (2000). Clinical significance of hepatitis C virus genotypes. Clin. Microbiol. Rev.
13:223-235.