Executive Summary: Modelling the Incidence and Prevalence of Hepatitis C Infection and its Sequelae in Canada, 2007
In 1998, a working group evaluated the extent of hepatitis C infection transmitted through blood transfusion in Canada and estimated that a total of about 240,000 persons were infected with hepatitis C in Canada as of July 1998. The working group, however, did not examine specifically the distribution of HCV infection among persons in other exposure categories (such as injection drug use, the most common source of infection) nor did they attempt to estimate the current or future impact of HCV infection.
In 2003, Health Canada wished to re-examine the estimated prevalence of HCV infection in Canada in 2002 and to obtain more detailed estimates by exposure category. For this purpose, Remis and his colleagues developed a novel actuarial approach using a three-stage model, including estimating the populations at risk by place of birth and exposure category, modelling HCV incidence and prevalence among those born in Canada and HCV prevalence at the time of arrival and subsequent HCV incidence for persons born elsewhere and, finally, projecting the outcomes of chronic HCV infection among those infected. The objectives of the HCV modelling study were to estimate the following parameters: hepatitis C incidence and prevalence, the proportion of HCV infections diagnosed, the number of persons living with HCV infection by stage of disease, HCV-related morbidity and the future occurrence of serious complications of HCV infection.
More recently, the Public Health Agency of Canada wished to update the 2002 estimates, incorporating new data on HCV progression and reported HCV cases and incorporating refinements to the analytic approach developed since 2002.
HCV-infected persons may eventually develop serious complications. This was assessed by estimating the number of persons progressing through the following clinical stages: cirrhosis, decompensated cirrhosis (liver failure), hepatocellular carcinoma, liver transplant and liver-related death. The model used annual transition parameters based on published data and modelling studies, incorporating the modifying factors age, sex and HIV status. The model was treated as an integrated continuum from entry through birth or immigration and then transition to exposure-related behaviours or experiences, mortality, HCV infection and progression to serious HCV disease. Estimations and projections of HCV infection, prevalence and sequelae were made from 1960 to 2027.
The results of our updated study may be summarized as follows. We estimated that approximately 242,500 persons in Canada were infected with HCV as of December 2007 and that about 7,900 persons were newly infected in 2007, mostly through injection drug use. The distribution of prevalent HCV infections by exposure category (to the nearest 100) was: injection drug use 52,500, ex-injection drug use 87,500, blood transfusion recipients 25,900, hemophilia patients 900, and “Other” 75,800. In our analysis, IDU accounted for 58% of prevalent HCV infections in Canada, blood transfusion 11%, hemophilia 0.4% and other modes of transmission 31%. Overall, it was estimated that about 192,000 (79%) of HCV-infected persons living in Canada as of December 2007 have been diagnosed.
The impact of the sequelae of hepatitis C infection on the health of Canadians appears to be considerable. In 2007, we estimated that 15,800 persons were living with cirrhosis and 5,500 with liver failure. The annual incidence of newly developing cirrhosis appeared to peak in the late 1990s and early 2000s but, according to the results of our model, the incidence of the more serious outcomes of HCV infection will continue to rise, at least until 2027. We estimated that from 2007 to 2027 the number of prevalent cases of cirrhosis will go from 15,814 to 17,570 and carcinoma will increase from 338 to 379 cases (Table 7b).
We also examined HCV prevalence in two special populations, namely persons of Aboriginal origin and persons incarcerated in federal and provincial prisons. We concluded that approximately 34,900, or 3.0%, of Aboriginal persons were HCV-infected and 6,300 or 18.7% of incarcerated persons were HCV-infected. The distribution of HCV-infected prisoners by type of institution was 2,700 and 3,500 in provincial and federal prisons, respectively.
There are several important lessons to be learned from our study. The impact of this disease on the health of Canadians is considerable. It is essential to encourage the estimated 50,000 HCV-infected persons who remain undiagnosed to undergo HCV testing. Otherwise these infected individuals might unknowingly spread the virus to others and do not benefit from treatment and care. It is important to provide health care services to HCV-infected patients; this includes specialized physician and laboratory services and provision of effective antiviral drugs. Further research is also required at many levels, including studies to: better evaluate the extent and the factors responsible for HCV infection in Canada. Finally, it would be important to undertake necessary research to obtain population-based estimates of HCV prevalence and incidence in the Canadian population, develop more effective programs to prevent new infection, better understand HCV infection and disease and develop and implement more effective methods of treatment. These suggested improvements to the HCV program will reduce the burden of disease and associated health costs.
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