Public Health Bulletin Edition 1, 2004 - SA Health - SA.Gov.au

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Hepatitis C Infection in Australia – An Ongoing Epidemic Emma R Miller Epidemiologist Department of Health Infection with the hepatitis C virus (HCV) is one of the most commonly notified diseases in South Australia. Since mandatory notification began in 1995, over 12,500 cases have been notified to the State surveillance system (State Surveillance data, Communicable Disease Control Branch, Department of Human Services, 2004). Around 20,000 HCV cases are newly notified across Australia each year (Communicable Diseases Australia, National Notifiable Diseases Surveillance System, Commonwealth Department of Health and Ageing, 2004). Infection with HCV has an extremely high chronicity rate (around 80% of those infected will fail to clear the virus), 1, 2 which has contributed to a nationwide prevalence of approximately 1.5% in Australia and in most other developed countries. 3 There are some potentially serious sequelae of HCV infection, the most serious of which is the association between long term infection with the virus and hepatocellular carcinoma (liver cancer). As stated by Farrell 4 (page 285); “From a community point of view, the problem of liver cancer is one of the most important issues that arise from the hepatitis C epidemic.” While only a small proportion of those infected will go on to develop serious health consequences, the sheer number of Australians now thought to be infected by the virus, over 200,000 according to recent estimates, 5 has substantial implications for public health and health service planning. Natural history There are six major strains of the HCV virus (a member of the flaviviridae family) and over 50 additional subtypes. 6 Moreover, the virus mutates very rapidly to form multiple quasi species. These are thought to be the chief mechanism by which the virus evades host immune systems, resulting in the low rate of viral clearance. 4, 7 The six strains have a differential geographical distribution, with types 1 to 3 being most common in Australia – around 55% of cases are thought to be type 1. 8, 9 29 The different genotypes of HCV do not appear to have a role in severity of disease, or disease outcome, but are strongly associated with response to treatment. Currently the only treatment available for chronic infection is Interferon in combination with Ribavirin. A number of unpleasant side effects are associated with interferon therapy, and the treatment course is long. The full treatment course is six months for HCV other than type 1, and 12 months for type 1. The overall treatment success (as evidenced by the sustained absence of detectable viral particles in the blood) is around 55%. Treatment success is lower in genotype 1, despite the longer duration of treatment. 10 Whether due to the duration of treatment, the associated side effects, or the difficulty of ‘selling’ a fairly aggressive therapy to patients with few apparent symptoms, treatment uptake remains relatively low in Australia. 3 Many of the symptoms associated with HCV-infection tend to be non-specific, if present at all; thus, many people are not diagnosed until they have been infected for many years. Disease progression usually occurs over a relatively long duration of infection, but can result in very serious health outcomes. Liver cirrhosis will occur in around 20 percent of those chronically infected, within approximately 20 years. Of those with cirrhosis, five to 10 percent will develop end-stage liver disease or hepatocellular carcinoma (cancer of the liver) within approximately 40 years of infection. 11, 12 Extrahepatic manifestations (non-liver related conditions) associated with chronic HCV-infection include poly sialadenitis (affecting salivary glands and producing dental problems), cryoglobulinaemia (leading to arthritis and skin disorders) and membranoproliferative glomerulonephritis (kidney disease). 1, 13-15 Even in the absence of liver damage or other clinically measurable signs, many people report various symptoms, including fatigue, depression and nausea. 16, 17 Studies have found that health-related quality of life in HCVinfection is significantly reduced in people with HCVinfection, irrespective of the stage or grade of their disease. 18, 19 Epidemiology There have been approximately 12,500 notifications of HCV to the State surveillance system since mandatory notification began in 1995. The majority of new notifications come from people who may have been infected for a very long time. The ability to plan preventive strategies requires that there be some way of identifying those
people who have only recently become infected. Since very few cases have a noticeable ‘seroconversion’ illness (jaundice, fever, etc) soon after they are infected, new infections (or ‘incident’ cases) are generally determined on the basis of the individual having had a negative test within 12 months prior to testing positive to HCV antibodies. Because most people are not serially tested in this way, the current case definition results in the majority of new infections remaining unidentified. In addition, the narrow case definition introduces a bias which is reflected in the demographics of the cases. For instance, incidence cases are identified in people who are more likely to be female and tend to be younger than other notified cases. Trends Chart 1 presents monthly notifications to the South Australian Surveillance system since January 1998. As can be seen, while notifications of new infections have been relatively consistent over time (at roughly, 70 notifications per year), the overall number of notifications appears to be declining over time. *All other groups: total incident cases; people identifying as Indigenous; people 21 years or younger; people over 55 years Source: Communicable Disease Control Branch, DHS - 2004 It is probable that the decreasing trend observed for non-Indigenous males aged between 22 and 55 years represents the gradual ‘mop up’ of cases that have been infected for many years prior to diagnosis. It is important to note that the HCV test has only been available for the last 12 years. Since chronic infection with HCV follows a very long and (often) symptomless course (as discussed above), the slow pick up of cases in males of this age is likely to reflect the slow rates of health service access known to occur in this group. Source: Communicable Disease Control Branch, DHS - 2004 Further analysis of the surveillance data reveals that the decline is mainly occurring in only one specific group of non-incidence notifications, that is, non-Indigenous males aged between 22 and 55 years. Since this group also makes the largest contribution to overall HCV notification numbers, the decrease in these numbers has the biggest impact on apparent overall trend. As demonstrated in Chart 2, non-incidence notifications for non-Indigenous females of the same age have also declined, but less steeply and with less impact on overall trend. No trends have been observed over time for any other group (Indigenous people, young people, or old people) when analysed separately or combined (see Chart 2). Risk factors Since the introduction in 1990 of the screening of blood products for HCV, injecting drug use (IDU) has been recognised as the major risk factor for infection. Chart 3 presents pooled data for all notifications from January 1998 to December 2003. As can be seen, IDU is reported as the primary risk factor for 60% of all notifications, and as one amongst other risk factors in a further 12% of notifications. Household contact with an infected person, medical procedures, and mother-to-child transmission are reported in very low numbers. These factors combined make up less than one percent of notifications over the five years. Source: Communicable Disease Control Branch, DHS - 2004 30 Two specific population groups continue to be overrepresented in the notification data. Firstly, notifications from people identifying as Indigenous make up approximately six percent of all notifications, despite representing less than two percent of the South Australian
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Public Health Bulletin Edition 1, 2004 - SA Health - SA.Gov.au

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