[Table of Contents]

Volume: 25S2 - June 1999

Hepatitis C - Prevention and Control: A Public Health Consensus

Background

Hepatitis C

Hepatitis C virus (HCV) is an enveloped RNA virus belonging to the Flaviviridae family and one of the five viruses that account for most cases of viral hepatitis. There are at least six genotypes of HCV and many more subtypes; genotype 1 is the commonest genotype in Canada, accounting for perhaps two-thirds of cases.

It is estimated that up to 3% of the world's population is infected with HCV, i.e. up to 170 million chronic carriers. The majority of those newly or chronically infected have no symptoms and are, therefore, often unaware of their infection; however, they serve as a source of transmission of infection and are at risk for chronic liver disease, cirrhosis, and liver cancer. Unpublished population-based studies in the United States indicate that 40% of chronic liver disease may be attributable to HCV infection.

In Canada, national reporting of HCV infection was started in 1992, and it is expected that infection will soon be reportable in all provinces and territories^d. The number of cases reported has increased dramatically from 1992 (1,321 cases) to 1997 (19,571 [provisional]), mainly because of increased recognition of previously acquired infection. Although there are no direct measurements, it is reasonably estimated that the prevalence of HCV infection in Canada is about 0.8% (240,000 persons), and of these people probably only about 30% are aware of their infection⁽¹⁾. Since most newly acquired cases are clinically silent and there is no laboratory test to distinguish such cases from chronic cases, it is difficult to measure incidence; while cautious interpretation is prudent, applying U.S. projections to the Canadian situation^e predicts approximately 2,200 new cases per year in Canada at this time.

Injection drug use (IDU) is the most important exposure for HCV infection in Canada, accounting for perhaps 70% of all prevalent infections. Among IDU cohorts in Vancouver and Montreal, the prevalence of HCV is reported as 85% and 70% respectively, and the annual incidence is reported as 26% and 27% respectively. On the basis of studies in other countries, the highest risk period for HCV acquisition through IDU is early after initatiting the behaviour. The overall control of HCV infection in Canada depends primarily on interventions for IDU.

Therapeutic blood exposure accounted for perhaps 10-15% of incident infections in the past, but the current risk is quite low, perhaps 1 in 103,000 donations.

In about 85% of newly acquired HCV infection, the infection becomes chronic. However, the progression of chronic hepatitis C disease is usually slow and may not be manifest during the first two decades following infection. However, given that many cases of chronic HCV infection in Canada were acquired in the remote past, perhaps 15-25 years ago, it is expected that there will be substantial increases, of the order of a doubling or tripling (or more), in disease sequelae of HCV infection in Canada over the next decade, e.g. cirrhosis, liver failure, deaths due to liver disease and the need for liver transplants.

LCDC National Conferences

In December 1994, the Laboratory Centre for Disease Control (LCDC) held a national meeting on the prevention and control of hepatitis C; the results and recommendations of the conference were published in July 1995⁽²⁾. Given that four years have passed since then, a second conference, Hepatitis C: Prevention and Control - A Public Health Consensus, was held from October 14-16, 1998, in order to review the present state of knowledge and action with regard to public health aspects of hepatitis C and to update the recommendations accordingly. Participants were assigned to one of six working groups, covering the fields of surveillance, public health interventions, public health laboratory issues, injection drug user issues, education and blood supply issues. The recommendations of these groups are presented in the next section.

^d As of January 01, 1999, HCV infection was reportable in all Canadian provinces and territories.
^e In the United States there are an estimated 36,000 incident cases per year at this time arising from 3.9 million prevalent cases. Applying the proportion 36,000/3,900,000 to the estimated 240,000 prevalent cases in Canada predicts 2,200 incident cases per year in Canada. The United States reports a marked decrease in incidence over the last decade; however, it is not clear that this has occurred in Canada.

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