Prevalence and incidence are two basic measures of disease frequency used to inform our response to the Hepatitis C (HCV) epidemic. Prevalence is the total number of people living with chronic HCV infection, while incidence is the number of new infections that occur in that year.
HCV surveillance in British Columbia relies on diagnoses of HCV in BC, which are looked at two ways:
- The number of new HCV diagnoses reported each year or first-time HCV positive individuals (reactive for antibody to hepatitis C virus or anti-HCV positive); and
- The number of acute cases – new positives with a negative anti-HCV test on record within the prior 12-month period.
These data are imperfect estimates because they only include individuals who have gone for testing, and tests can be done years after initial infection. For HCV incidence, looking at acute cases is a reasonable estimate, but these trends are also influenced by testing behavior (and are more likely to reflect people who test for HCV more frequently).
The Public Health Agency of Canada (PHAC) released a surveillance report summarizing hepatitis C in Canada from 2005 – 2010, based on based multiple data sources. This includes the last release of modeled estimates of HCV prevalence and incidence from 2007. Below we describe findings from the Canadian surveillance report and provide the most recent HCV diagnosis trends from British Columbia surveillance data.
As a chronic condition, HCV prevalence increases over time as cases accumulate. To understand the scope of problem, in 2007, a model was developed to estimate the number of HCV cases in Canada.
- It was estimated that 242,521 people were living with HCV in Canada, corresponding to a prevalence of 0.8% of the general population (Table 1). The prevalence of HCV among males was 1.6 times higher than among females.
- Incidence was modeled at 0.026% or about 8000 persons with newly-acquired infection in 2007. Incidence among males was higher than females and more than three quarters (83%) of incident infections were among persons who inject drugs (PWID).
The annual numbers and rates of laboratory confirmed infections (anti-HCV testing) reported to the Canadian Notifiable Disease Surveillance System (CNDSS) decreased between 2005 and 2009 from 13,017 cases in 2005 to 11,357 in 2009, corresponding to a rate of 40.4 per 100,000 in 2005 to 33.2 per 100,000 in 2009 for Canada. While BC rates are also decreasing, rate of new HCV diagnoses in BC is still higher than most other provinces and the national average (Figure 1).
Incidence in BC, as represented by rates of acute cases, has been decreasing since 2008 (Figure 2). Increases in testing volume (over 130,000 persons tested for hep C in 2011) and repeat testing behaviour (testing more than once) have helped to improve this estimate over time.
Interpretation and implications
The decreasing trend in hepatitis C case reports in British Columbia and Canada is thought to be due to a reduction in transmission/incidence related to decrease in illicit drug injection use and/or low numbers of susceptible (uninfected) persons in the key risk population, PWID. There are various HCV risk groups with varying rates of HCV infections. While PWID are a major contributor to the pool of HCV infected individuals in Canada, other risk factors include:(1)
- history of haemodialysis,
- receipt of blood products before 1992 or clotting factors before 1988,
- exposure to blood of high risk individual,
- unregulated tattoos,
- immigration from a high-prevalence country and
- those presenting with HIV and/or persistently elevated liver enzymes (AST).
While current BC specific estimates of HCV prevalence are not available, there may be 60,000 to 80,000 persons infected with HCV in BC, many unaware of their infection. A recent study of British Columbians who underwent anti-HCV testing found high death rates in HCV positive individuals due to progressive liver disease as well as risks related to drug use, street involvement and poverty.(2) In 2011, about one in three HIV positive individuals in BC were also infected with HCV.(3) All of this suggests that British Columbians with hepatitis C have a spectrum of risks, needs, and health outcomes requiring very different prevention and treatment approaches.
At this time, there are multiple initiatives underway to improve provincial HCV and HIV surveillance data and derived estimates by incorporating other information that would confirm infection and link to important health outcomes, such as treatment and mortality, as well as inform prevention initiatives.
National estimates are presented in more detail in Hepatitis C in Canada: 2005-2010 Surveillance Report.
Provincial estimates of Hepatitis C rates can be found in British Columbia Annual Summary of Reportable Diseases, 2011.
PHAC = Public Health Agency of Canada
BCCDC = British Columbia Centre for Disease Control
CNDSS = Canadian Notifiable Disease Surveillance Systems
PWID = Persons who inject drugs
- Mark Gilbert, Physician Epidemiologist, Clinical Prevention Services, BCCDC
- Naveed Janjua, Hepatitis Surveillance Lead, Clinical Prevention Services, BCCDC
- Travis Salway Hottes, Epidemiologist, Clinical Prevention Services, BCCDC
- The Society of Obstetricians and Gynaecologists of Canada. The Reproductive Care of Women Living with Hepatitis C Infection. SOGC Clinical Practice Guidelines. 2000.
- Yu A, Spinelli JJ, Cook D, Buxton JA, Krajden M. Mortality among British Columbians testing for hepatitis C antibody. BMC Public Health. 2013;13:291.
- Klein MB, Rollet KC, Saeed S, Cox J, Potter M, et al. HIV and hepatitis C virus coinfection in Canada: challenges and opportunities for reducing preventable morbidity and mortality. HIV Medicine. 2013;14:10-20.