Final Report: Estimating the Number of Persons co-infected with Hepatitis C Virus and Human Immunodeficiency Virus in Canada

1. Introduction

1.1 Background

Co-infection with hepatitis C virus (HCV) and the human immunodeficiency virus (HIV) is of particular interest, since persons infected with both viruses may have an aggravated clinical course related to the presence of the other infection. In particular, the immune suppression caused by HIV may exacerbate the progression of hepatic disease due to HCV infection. The treatment of each infection may also be complicated by the presence of the other infection. Thus, dual infection with HCV and HIV is important due to the considerable burden of illness posed by both viruses and to the specific challenges in determining the appropriate treatment for each of these serious viral infections.

The number of HCV-HIV co-infected individuals is likely to be considerable since the modes of transmission for the two viruses overlap to a significant extent. Both HCV and HIV may be acquired through parenteral exposure, particularly related to, though not limited to, injection drug use and the receipt of blood transfusions and plasma fractionation products (in particular, clotting factors). The risk of acquisition of these viruses from blood transfusions and plasma derivatives was markedly reduced in Canada with the implementation of specific serologic screening tests. Testing for HIV was initiated in November 1985, while HCV testing began in May 1990. Nevertheless, a substantial number of persons who were infected before these measures were put in place are still alive, and injection drug users continue to become infected with HIV and HCV at a significant rate.

With respect to hepatitis C, the most important exposures in Canada are historically related to injection drug use, blood transfusions and the receipt of plasma fractionation products. Because there is more data, and more reliable data, on HIV prevalence, calculating the number of co-infections is best achieved by first estimating the number of HIV-infected persons in each HIV-defined exposure category, then multiplying this number by the prevalence of hepatitis C infection within each group based on data from Canada and comparable populations elsewhere.

We examined seven exposure categories in all: men who have sex with men (MSM), injection drug users (IDUs), MSM-IDU, persons from HIV-endemic countries, other persons infected by heterosexual contact, patients with hemophilia, and transfusion recipients. MSM (because they comprise the largest group of HIV-infected persons in Canada) and persons who inject drugs (because of the high rate of both infections) likely account for most of the HCV-HIV co-infections in Canada. Though most hemophilia patients are infected with hepatitis C, the number of surviving HIV-infected persons in this group is relatively small.

1.2 Mandate

The number of persons with HCV-HIV co-infection in Canada is currently unknown. This study is being undertaken since dually-infected persons with HCV and HIV have particular concerns relating to prognosis and antiviral treatment of each of the diseases as noted above. Therefore, we were asked to undertake a modeling analysis to estimate the number of HCV-HIV co-infected persons stratified by exposure category and region of residence. To the extent feasible, we were also asked to estimate the number of co-infections occurring specifically among Aboriginal persons and prisoners.

This study was mandated by the Hepatitis C Division, Population and Public Health Branch, Health Canada. The present report integrates the results of two previous stages of the analysis. In the first stage, we determined the number and plausible range of HIV-infected persons in Canada. In the second, we estimated the HCV prevalence among each of these groups, and then applied this prevalence to the number in each group to determine the number of HCV-HIV co-infected persons.

1.3 Study objectives

The objectives of the study were:

1. To update the estimates of the number of HIV infected-persons by exposure category and geographic region as of December 1999;
2. To review the literature to determine the likely prevalence of HCV among HIV-infected persons in each of these groups;
3. To determine the number and the plausible range of HCV-HIV co-infected persons in Canada by exposure category and geographic region; and
4. To carry out a similar analytic process as in Objective 3 for the Aboriginal population and for persons incarcerated in federal and provincial prisons in Canada.

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