Section 1: Modelling the Incidence and Prevalence of Hepatitis C Infection and its Sequelae in Canada, 2007 – Introduction

1. Introduction

1.1 Background

A serologic test for the hepatitis C virus (HCV) was developed in 1989. In the ensuing several years, seroepidemiologic studies were undertaken throughout the world to better characterize the distribution and natural history of HCV infection. It soon became clear that, in most Western industrialized countries, injection drug use was responsible for the majority of both prevalent and incident HCV infections. Following the realization that clotting factors and blood transfusion could also transmit HCV and accounted for 15-20% of HCV infections, routine HCV screening of plasma and blood donors was rapidly implemented, beginning in 1990. Donor screening markedly reduced, though not immediately, transfusion-transmitted infections and most of the residual incident HCV infections were due to injection drug use.

Though the first serologic HCV test was licensed in 1990, diagnostic testing on a large scale did not occur immediately in part due to the lack of clear guidelines for its use and the lack of effective treatments. HCV testing began on a broad scale in the mid-1990s. In the early to mid-1990s, HCV infection became reportable in most Canadian provinces. As of 2002, HCV reporting was mandatory in all provinces and territories.

In 1998, we carried out a modelling study for the Laboratory Centre for Disease Control, Health Canada to estimate the number of persons living as of July 1998 who were infected by hepatitis C through blood transfusion in Canada¹. In collaboration with an expert working group constituted for this purpose, we developed three independent models to “triangulate” the number of persons infected in the periods before 1986 and 1990 and after. One of these models involved the estimation of the total number of persons in Canada infected with HCV. This was stratified in the final output by province of residence based primarily on relative HCV prevalence among blood donors. We estimated that, as of July 1998, 240,000 HCV-infected persons were living in Canada, for a crude prevalence rate of 0.80%.

In early 2003, we were asked by the Hepatitis C Division, Centre for Infectious Disease Prevention and Control, Health Canada to update the HCV estimates to December 2002 and to estimate the number of HCV-infected persons stratified by exposure category². We were also asked to estimate the number of persons by stage of liver disease, including cirrhosis, decompensated liver failure, hepatocellular carcinoma, transplantation and HCV-related mortality. The findings were first presented at the 2nd Canadian Conference on Hepatitis C in Vancouver in March 2004. No province-specific estimates of hepatitis C infection or its sequelae were made in the course of this study.

The 2003 study also examined in a preliminary fashion the number of HCV infections reported since HCV testing became available. The estimate was preliminary in part because it was difficult to determine: 1) whether all reported infections had been validated; 2) the extent to which duplicates had been removed, and 3) if recent infections were effectively differentiated from remote infections. Also, data were missing in some jurisdictions for several of the early years and the most recent year. Nevertheless, we estimated that 156,590 infections had been diagnosed in Canada from 1991 to 2002, 52,390 (33%) of which were in Ontario.

In early 2008, the Community Acquired Infections Division, Centre for Communicable Disease and Infection Control, Public Health Agency of Canada wished to update the estimates of the incidence and prevalence of HCV infection and its sequelae in Canada.

1.2 Study objectives

The objectives of the present HCV modelling study were as follows:

1. Estimate the prevalence and incidence of HCV infection among persons living in Canada as of December 2007 by exposure category, age and sex;
2. Estimate the incidence and prevalence of serious sequelae among HCV-infected persons in Canada from 1960 to 2027;
3. Estimate the prevalence of HCV infection as of December 2007 by province and territory;
4. Estimate the number of persons with HCV infection incarcerated in provincial and federal prisons in Canada;
5. Estimate the number of Aboriginal persons with HCV infection living in Canada;
6. Estimate the number of persons diagnosed with HCV infection in Canada from 1991 to 2007; and
7. Estimate the proportion of persons living with HCV as of December 2007 who have been diagnosed (overall and by exposure category, if possible).