Vaccine Preventable Diseases and Vaccination Coverage in Aboriginal and Torres Strait Islander People, Australia, 2003 to 2006

Hepatitis A

Disclaimer: Produced by the National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases and the Australian Institute of Health and Welfare on behalf of the Australian Government Department of Health and Ageing. Published as a supplement to the Communicable Diseases Intelligence journal Volume 32, June 2008.

Page last updated: 30 June 2008

Acute infection with the hepatitis A virus (HAV), a picornavirus, presents a clinical spectrum from malaise and diarrhoea to acute hepatitis with jaundice to fulminant liver failure. Onset of symptoms is usually abrupt with fever, anorexia, malaise, nausea and abdominal discomfort followed by jaundice and dark urine.36,37 The single most important factor in determining the clinical presentation and outcome of HAV infection is age. Whilst only 10%–50% of infections acquired before the age of 5 years are symptomatic, 70%–95% of infected adults will show symptoms.38

Case definitions


Notifications

National definition from January 2004:10

Detection of anti-hepatitis A virus IgM antibody, in the absence of recent vaccination;

or

Detection of hepatitis A virus by nucleic acid testing;

or

Clinical hepatitis (jaundice and/or bilirubin in urine) without a non-infectious cause
and an epidemiological link to a laboratory-confirmed case.

(See Appendix D for pre-2004 definition)

Hospitalisations and deaths

The ICD-10-AM/ICD-10 codes B15 (hepatitis A) were used to identify hospitalisations and deaths.

Distribution by Indigenous status and age

Of the total 1,169 notifications of hepatitis A recorded in New South Wales, the Northern Territory, South Australia, Victoria and Western Australia over the four years from 2003 to 2006, 162 (14%) were identified as occurring in Aboriginal and Torres Strait Islander people (Table 2). For hospitalisations, 66 (11%) of the total 581 cases were in Aboriginal and Torres Strait Islander people in the three-year period July 2002 to June 2005 in New South Wales, the Northern Territory, Queensland, South Australia and Western Australia (Table 3).

Table 2. Hepatitis A notification rates, selected Australian states, 2003 to 2006, by age group and Indigenous status

Age group
(years)
Indigenous status
Notifications* (2003–2006)
n Rate Rate ratio
0–4 Indigenous
55
33.9
24.4||
Other
51
1.4
5–14 Indigenous
64
19.7
7.5||
Other
207
2.6
15–24 Indigenous
20
7.5
3.4||
Other
182
2.2
25–49 Indigenous
19
4.4
2.5||
Other
388
1.8
50+ Indigenous
4
2.7
2.9
Other
179
0.9
All ages Indigenous
162
8.1
4.9||
Other
1,007
1.7

* Notifications (New South Wales, the Northern Territory, South Australia, Victoria and Western Australia only) where the date of diagnosis was between 1 January 2003 and 31 December 2006.

† Average annual age-specific rate per 100,000 population.

‡ Rates for all ages combined are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2005.

|| Shaded cells indicate statistically significant, 95% confidence intervals greater than 1 (p<0.5).

Table 3. Hepatitis A hospitalisations and deaths, selected Australian states, 2002 to 2005, by age group and Indigenous status

Age group
(years)
Indigenous status
Hospitalisations*
(July 2002–June 2005)
Deaths
2003–2005
n Rate Rate ratio n
0–4 Indigenous
20
12.3
157.0||
0
Other
2
0.1
0
5–14 Indigenous
14
4.3
9.5||
0
Other
25
0.5
0
15–24 Indigenous
7
2.7
2.6
0
Other
60
1.0
0
25–49 Indigenous
21
5.0
3.1||
0
Other
245
1.6
0
50+ Indigenous
4
2.8
2.0
1
Other
183
1.4
0
All ages§ Indigenous
66
4.4
3.6||
1
Other
515
1.2
0

* Hospitalisations (New South Wales, the Northern Territory, Queensland, South Australia and Western Australia only) where the date of separation was between 1 July 2002 and 30 June 2005.

† Deaths (the Northern Territory, Queensland, South Australia and Western Australia only) where the death was recorded between 1 January 2003 and 31 December 2005.

‡ Average annual age-specific rate per 100,000 population.

§ Includes cases with unknown ages. Rates for all ages combined are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2005.

Shaded cells indicate statistically significant, 95% confidence intervals greater than 1 (p<0.5).

Both notification and hospitalisation rates were highest among children aged 0–4 years identified as Aboriginal and Torres Strait Islander (34 and 12 per 100,000, respectively). Figure 1 illustrates the striking difference between young children and others when comparing notifications for Aboriginal and Torres Strait Islander and other people. All the hospitalisations and notifications aged 0–4 years that were recorded as Aboriginal and Torres Strait Islander were from the Northern Territory, Queensland, South Australia or Western Australia. Of the 55 notifications recorded as Aboriginal and Torres Strait Islander in that age group, 9 (16%) were diagnosed in 2006.

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Figure 1. Hepatitis A notification rates, selected Australian states,* 2003 to 2006, by age group and Indigenous status

Figure 1. Hepatitis A notification rates, selected Australian states, 2003 to 2006, by age group and Indigenous status

* New South Wales, the Northern Territory, South Australia, Victoria and Western Australia.

† Notifications where the date of diagnosis was between 1 January 2003 and 31 December 2006.

The overall Indigenous to non-Indigenous rate ratio was 4.9:1 for notifications and 3.6:1 for hospitalisations and both ratios were statistically significantly above 1.0. In children aged 0–4 years, the rate ratios were higher and statistically significant, at 24 for notifications and 157 for hospitalisations. This excess morbidity falls sharply with age, with smaller but substantial Indigenous versus other rate ratios among children 5–14 years of age (7.5:1 for notifications, 9.5:1 for hospitalisations), decreasing to 3:1 or less from age 15 years.

Over the six-year period July 1999 to June 2005, the difference in hospitalisation rates for hepatitis A for Aboriginal and Torres Strait Islander and other people for all age groups has declined in both groups with a more marked decline in Indigenous rates (Figure 2). The higher rates in 1999/2000 and 2002/2003 correspond to periods of higher rates in Western Australia.

Figure 2. Hepatitis A hospitalisation rates, selected Australian states,* 1999 to 2005, by Indigenous status

Figure 2. Hepatitis A hospitalisation rates, selected Australian states, 1999 to 2005, by Indigenous status

* The Northern Territory, Queensland, South Australia and Western Australia.

† Hospitalisations where the date of separation was between 1 July 1999 and 30 June 2005. Rates are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2005.

During the period 2003 to 2005, there was one reported death due to hepatitis A in the Northern Territory, Queensland, South Australia and Western Australia. It occurred in an Aboriginal and Torres Strait Islander person aged over 50 years.

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Comment

In 1999, an immunisation program commenced for Aboriginal and Torres Strait Islander children, aged 18 months to 6 years living in north Queensland, which had a significant impact on reducing hepatitis A across the community.39 This program was expanded in November 2005 to include all Aboriginal and Torres Strait Islander children aged 12–24 months in the Northern Territory, Queensland, South Australia and Western Australia.40 The need for this program is underlined by the fact that all hospitalisations and notifications recorded as Indigenous in children aged 0–4 years in the period covered in this report were from these jurisdictions.

The pattern of acquisition of hepatitis A is known to vary substantially according to living standards. More advantaged communities have delayed or no exposure to hepatitis A, with the majority seronegative even in middle age. In contrast, communities living in crowded and/or less hygienic circumstances acquire infection and immunity to hepatitis A at an early age. In the Northern Territory in 1994, a serosurvey in rural Aboriginal populations found hepatitis A to be hyperendemic, with acquisition of the virus predominately in the first five years of life.41 Temporal trends in hepatitis A are dominated by sporadic cases, point-source outbreaks and community epidemics. The decline in hospitalisation rates in non-Indigenous people seen in Figure 2 coincides with the end of an epidemic focused on men who have sex with men and injecting drug users,42–45 while the more variable pattern in Aboriginal and Torres Strait Islander hospitalisations may be due to lower numbers and/or reflect local outbreaks. It may also show some impact of vaccination in north Queensland, but the data end shortly before the commencement of the expanded national program.

In the United States, hepatitis A cases decreased substantially following the recommendation of vaccination of children in communities with high rates of disease in 1996, and for children in states and counties with high hepatitis A notification rates in 1999. In 2006, this was expanded to include all US infants, as part of a staged implementation of progressively expanded vaccination.46 Continued monitoring should be a priority in Australia, both to assess the impact of these recent changes, and the need for any further expansion of vaccination.

Aboriginal and Torres Strait Islander people of all ages experience rates of hepatitis A significantly higher than presumed non-Indigenous Australians. The rates per 100,000 are highest for young Aboriginal and Torres Strait Islander children less than 5 years of age. It is hoped that the recently commenced Indigenous childhood vaccination program in four jurisdictions will have a substantial impact on this discrepancy.