1.0 Prevalence and epidemiology of hepatitis B

 

KEY POINTS
  • In 2011, there were an estimated 218,000 people living with chronic hepatitis B (CHB) infection in Australia, representing 1% of the population.
  • Only 56% of people living with CHB in Australia are believed to have been diagnosed.
  • Those born overseas and Aboriginal and Torres Strait Islander people comprise around two thirds of all Australians living with CHB.
  • A higher prevalence of CHB infection is also observed in people who inject drugs and in men who have sex with men.
  • Over 90% of new cases of CHB in Australia are attributable to migration and cannot be prevented through local vaccination initiatives.
  • Deaths due to CHB result from complications of cirrhosis, liver failure and liver cancer (specifically, hepatocellular carcinoma) in up to one quarter of people living with CHB.

The global burden of hepatitis B virus (HBV) infection is profound. Between 240 and 350 million people are estimated to be living with chronic hepatitis B (CHB) and over 2 billion have been infected (1, 2). CHB causes liver-related death in up to one quarter of people affected Lavanchy D. Hepatitis B virus epidemiology, disease burden, treatment, and current and emerging prevention and control measures. J Viral Hepat. 2004;11(2):97–107(1), making hepatitis B the second most important known human carcinogen after tobacco (3). HBV is the leading cause of liver cancer worldwide, with 70–85% of these liver cancers being hepatocellular carcinoma (HCC) (4). The Global Burden of Disease Study estimated that HBV infection was responsible for 786,000 deaths in 2010 (5).

Although the prevalence of CHB varies significantly by country, most people in the world live in an area endemic for hepatitis B (considered as >2% prevalence), and about 45% live in an area of high (>8%) prevalence (see Figure 1.1). HBV is transmitted through blood or infected bodily fluids; for example, by mother-to-child transmission, sexual contact or percutaneous exposures (1). HBV infection is not transmitted through sharing food or casual contact.

The epidemiology of CHB is predominantly determined by the age at exposure, with about 90% of infected infants progressing to chronic infection, compared with only 5% of immunocompetent adults (1) (see Chapter 4). This is why most people currently living with CHB in Australia acquired infection early in life (as is the case globally), and why universal infant vaccination is crucial for HBV control across populations. Although most countries have now implemented universal infant vaccination, the long delay between initial infection and the onset of complications, and the large number of existing chronic infections, means that the burden of disease attributable to CHB will remain high for several decades. Early diagnosis and appropriate management for those affected are essential for addressing the increasing morbidity and mortality associated with CHB.

Figure 1.1 Geographical distribution of hepatitis B virus (3)

In 2011, an estimated 218,000 Australians (about 1% of the population) were living with CHB (6). The priority populations affected by CHB in Australia include those born overseas in endemic areas (particularly the Asia and Pacific regions) (Figure 1.2), Aboriginal and Torres Strait Islander people, people who inject drugs, and men who have sex with men (MSM); these groups make up over three quarters of those affected (Figure 1.3). Other Australian-born people at higher risk for CHB include those whose parents were born overseas in an endemic area, and those exposed to hepatitis B through sexual contact or medical transmission before routine blood donor screening.

The prevalence of CHB in Australia has increased over the past decade, predominantly related to the increases in migration from endemic areas such as the Asia and Pacific regions (7, 8) and sub-Saharan Africa. Other areas with an increased prevalence of CHB include parts of Southern and Eastern Europe, and the Middle East (see Figure 1.1).


Proportion of people with Chronic Hepatitis B (CHB) in Australia, 2011 (%)
Figure 1.2 Top countries of birth for chronic hepatitis B in Australia (6)

 

Figure 1.3 Distribution of Australia’s burden of chronic hepatitis B by priority population (6)

 

Australia implemented universal infant vaccination for hepatitis B in 2000 (9), as well as adolescent catch-up programs, which have been effective in reducing the number of people acquiring hepatitis B in adulthood (10) and will help prevent transmission to children born in Australia to mothers with CHB. However, given the large number of people already living with CHB and that most new CHB infections are entering the population through migration (6), vaccination programs are unlikely to have a substantial effect on morbidity and mortality associated with hepatitis B; instead, diagnosis and clinical management are the key components of an effective response (11).

Diagnosis of CHB requires notification to the relevant public health authority in all Australian states and territories. The rate of CHB diagnosis has remained relatively stable over the past decade, with about 7,000 new diagnoses annually (Figure 1.4); however, it is estimated that only about half of those living with CHB in Australia have been diagnosed (6). Newly acquired (acute) HBV infections represent about 5% of all notifications of hepatitis B. Notifications of newly acquired HBV infection fell over the course of the past decade, partly because of the impact of the universal infant and adolescent vaccination programs mentioned above.

This increasing prevalence and the large number of people living with undiagnosed infection is contributing to a rising burden of advanced liver disease, including HCC (6, 12-14). Liver cancer is now the ninth most common cause of cancer mortality in Australia, and mortality is increasing faster than for any other cause of cancer death (15, 16).

Most of the liver cancer in Australia is thought to be attributable to chronic viral hepatitis (B and C) (17), and the burden is greatest in Aboriginal and Torres Strait Islander people (18), and those born overseas (7, 19).

 

Figure 1.4 Notifications of hepatitis B to Australia’s National Notifiable Diseases Surveillance System, 2003–12

 

1.3.1 Culturally and linguistically diverse communities

In the 2011 Census, about six million Australians (27%) were born overseas (20), with around 40% of these migrating from regions with a population CHB prevalence of 2% or more (20, 21). The prevalence of CHB in migrants generally reflects that of their country of origin (22, 23) and in Australia, particularly in urban areas, the prevalence of CHB by geographic area reflects the proportion of residents who were born overseas (8, 24).

When considering Australians born overseas living with CHB, the largest group consists of those born in the Asia and Pacific regions (38% of all Australians living with CHB). People born in Africa and the Middle East (7% of the total) and Europe (10% of the total) also make up a substantial proportion of people with CHB in Australia (6). This is reflected in the finding that Australians born overseas in HBV endemic areas have a much higher incidence of liver cancer than non-Indigenous Australian-born individuals, with those born in countries such as Cambodia, China, Korea and Vietnam up to 10 times more likely to be diagnosed with liver cancer than other Australians (7, 19).

1.3.2 Aboriginal and Torres Strait Islander Australians

According to the 2011 Census, there were 517,000 Aboriginal and Torres Strait Islander Australians, representing 2.6% of the population (20). However, Aboriginal and Torres Strait Islander people are estimated to account for 10% of Australians living with CHB infection (6).

The prevalence of CHB in Aboriginal and Torres Strait Islander people has decreased over the past two decades, from an estimated 16% to 4%, but it remains four times higher than in non-Indigenous people (25). One explanation for this reduction in prevalence is the implementation of universal infant and adolescent vaccination programs. Despite these successes, there is evidence of gaps in the immunity of Aboriginal and Torres Strait Islander people. Several studies have demonstrated significant numbers of Aboriginal and Torres Strait Islander people lack markers of immunity to HBV infection (26, 27), and only 85.5% of children have been fully vaccinated (receiving three doses by 12 months of age), as compared to 92.1% of non- Indigenous children (28). Importantly, there is also evidence of vaccination failure even in children who were documented to have received a full course of vaccine (29). Further studies of the reasons for failure of vaccination policy in Aboriginal and Torres Strait Islander people are required (see Chapter 5).

The incidence of HCC has been demonstrated to be two to eight times higher in Aboriginal and Torres Strait Islander people compared with non- Indigenous Australians, in a number of areas of Australia (18). People living in remote areas of Australia often have limited access to primary health care and specialist services. A higher proportion of Aboriginal and Torres Strait Islander people compared with non-Indigenous Australians live in remote areas (25% compared to 2%) (30), with people living in remote areas often needing to travel great distances to access health services.

This was highlighted in a study conducted in the Torres Strait Islands, which outlined a range of barriers for community members in accessing HBV testing, vaccination and ongoing management, together with numerous issues for clinical staff around workforce development, training and mentorship (31).

1.3.3 People who inject drugs

A recent systematic review suggested that 4% of Australians who currently or recently injected drugs are living with CHB (32). Given that about 1.5% of the Australian population has injected drugs at some time (33), a conservative estimate of the number of people with a history of injecting drug use living with CHB is about 12,500, or 6% of all Australians living with CHB. Australian seroprevalence studies in people who inject drugs have shown that only about one quarter of participants had serological markers of immunity to HBV infection (34, 35), with a longer history of injecting and exposure to hepatitis C being independently associated with HBV infection.

1.3.4 Men who have sex with men

The prevalence of CHB among MSM is around three times higher than the population prevalence in Australia, and MSM are estimated to comprise around 4% of all people living with CHB (6). Although the prevalence has declined among the MSM population since the 1980s, recent studies still indicate an increased risk in this community; for example, a sexual health clinic in Melbourne found a prevalence of 3% (36). Levels of immunity through both prior infection and immunisation have been demonstrated to be high, with studies involving men in Melbourne and Sydney showing that more than half had serological evidence of immunisation (37). Factors associated with increased risk of HBV infection among MSM include increased age, a higher number of sexual partners, and a history of sexually transmissible infections (36, 37).

 People born overseas in areas with 2% HBV prevalence or greater (see Figure 1.1)
 Aboriginal and Torres Strait Islander people
 People who inject drugs
 Men who have sex with men
 People living with HIV and/or hepatitis C
 Sex workers
 People with haemophilla/history of blood transfusion in the pre-screening era
 People with multiple sexual partners
 Household and sexual contacts of people with CHB
 People who are undergoing dialysis
 People who have ever been in custodial settings
Table 1.1 People recommended for routine CHB screening in accordance with the National Hepatitis B Testing Policy (see testingportal.ashm.org.au/hbv)

1.3.5 Other priority populations

A number of other population groups are identified as being at increased risk of HBV infection, including commercial sex workers (38), people in correctional facilities (39), people with haemophilia or a history of transfusion conducted before the implementation of screening in the late 1970s, and people born in Australia to mothers from endemic areas prior to commencement of universal infant vaccination in 2000. People living with human immunodeficiency virus (HIV) or hepatitis C, or both, are at increased risk HBV infection, and of experiencing severe acute infection and (for HIV) progression to chronic infection. A comprehensive list of populations recommended for routine testing in Australia is given in Table 1.1.

Understanding the epidemiology of CHB is crucial to identifying those at risk and guiding screening activities, but also for delivering appropriate and effective care to those groups disproportionately burdened.

Many people who belong to communities at greater risk for CHB have low awareness about hepatitis B, even when engaged with health-care services (40, 41). This situation highlights the need for improved targeting and engagement of high-risk groups by clinicians.

Those Australians born overseas, and Aboriginal and Torres Strait Islander people, often have lower rates of participation in preventive care services such as cancer screening (18, 42). This has significant implications for the clinical management of people from these populations living with CHB, with ultrasound-based screening for liver cancer a key part of management for those at risk (see Chapter 9).

In addition to general practices and other primary health-care services in Australia, there are over 150 Aboriginal Community Controlled Health Services (ACCHS), which provide culturally appropriate medical and allied health care to Aboriginal people. Studies indicate that ACCHS are preferred primary health-care providers by Aboriginal and Torres Strait Islander people (43) and – with appropriate resourcing, training and support – have the potential to improve HBV testing uptake and vaccination coverage, plus provide ongoing monitoring and treatment for Aboriginal and Torres Strait Islander people living with CHB.

In Australia, CHB disproportionately affects those from culturally and linguistically diverse backgrounds, with more than two thirds of those living with infection born overseas or being Aboriginal and Torres Strait Islander people. Most people currently living with CHB acquired it at birth or in early childhood. Despite CHB affecting more than 220,000 Australians, only just over half have been diagnosed, highlighting the importance of routine CHB screening in these groups. Given growing migration from endemic areas of the world such as Africa, the Asia and Pacific regions and the Middle East, targeted testing must intensify to increase detection rates and avert further increases in adverse outcomes of CHB, such as liver cancer, which has become the fastest growing cause of cancer death in Australia.

Knowledge of the Australian communities most affected by CHB is essential when planning and implementing clinical and public health responses aimed at addressing the increasing burden of disease, low levels of disease awareness and diagnosis, and low treatment uptake. Such an epidemiological understanding will help to ensure that any interventions are effective, understood and appropriate for the communities most affected.

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Jennifer MacLachlan Victorian Infectious Diseases Reference Laboratory (VIDRL), and Department of Medicine, University of Melbourne, Melbourne, VIC
Simon Graham Kirby Institute, The University of New South Wales, Sydney, NSW
Benjamin Cowie Department of Medicine, University of Melbourne, WHO Regional Reference Laboratory for Hepatitis B VIDRL, and Victorian Infectious Diseases Service, Royal Melbourne Hospital, Melbourne, VIC