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

Pneumococcal disease

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

Pneumococcal disease is caused by the bacterium Streptococcus pneumoniae (pneumococcus). Pneumococci are frequently isolated from the upper respiratory tract and can spread directly from the nasopharynx to cause infection in other parts of the respiratory tract (otitis media, sinusitis, pneumonia) or enter the bloodstream. Following bloodstream invasion, clinical manifestations include meningitis, pneumonia and infection at a number of less common sites, as well as septicaemia without focal infection. Invasive pneumococcal disease (IPD) is defined as a sterile site isolate of S. pneumoniae, usuallyfrom blood. In the absence of a sterile site isolate, a presumptive diagnosis of pneumococcal pneumonia may be based on a sputum isolate of S. pneumoniae and/or clinical features such as the chest x-ray appearance and prompt response to antibiotic therapy.72

Case definitions


Notifications

From January 2001, invasive pneumococcal disease became notifiable Australia wide, with cases identified by:

Isolation of Streptococcus pneumoniae by culture from a normally sterile site;

or

Detection of Streptococcus pneumoniae from a normally sterile site by nucleic acid testing.

Hospitalisations

The ICD-10-AM codes used to identify invasive pneumococcal disease hospitalisations were: G00.1 (pneumococcal meningitis); A40.3 (pneumococcal septicaemia). Analysis of pneumococcal pneumonia hospitalisations used J13 (pneumococcal pneumonia), excluding records that also contained codes for invasive disease.

Deaths

ICD-10 codes G00.1 and A40.3 were used to select deaths from IPD.

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Distribution by Indigenous status and age

Of the total 5,941 notifications of IPD recorded in New South Wales, the Northern Territory, South Australia, Victoria and Western Australia over the four years from 2003 to 2006, 477 (8%) were recorded as occurring in Aboriginal and Torres Strait Islander people (Table 13). For IPD hospitalisations, 234 (11%) of the total 2,228 cases were recorded as Aboriginal and Torres Strait Islander in the three-year period July 2002 to June 2005 in New South Wales, the Northern Territory, Queensland, South Australia and Western Australia (Table 14).

Table 13. Invasive pneumococcal disease 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
106
65.2
1.8||
Other
1,315
35.8
5–14 Indigenous
40
12.3
4.6||
Other
212
2.7
15–24 Indigenous
35
13.1
5.8||
Other
187
2.3
25–49 Indigenous
219
50.9
11.2||
Other
1,003
4.5
50+ Indigenous
76
51.5
3.5||
Other
2,747
14.5
All ages Indigenous
477
41.7
4.6||
Other
5,464
9.0

* 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 14. Invasive pneumococcal disease 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
61
37.4
1.7||
0
Other
572
22.3
2
5–14 Indigenous
16
4.9
3.1||
0
Other
88
1.6
0
15–24 Indigenous
9
3.4
3.8||
0
Other
52
0.9
0
25–49 Indigenous
106
25.0
13.6||
0
Other
281
1.8
2
50+ Indigenous
42
29.4
3.8||
1
Other
1,001
7.7
4
All ages§ Indigenous
234
21.4
4.5||
2
Other
1,994
4.7
9

* 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).

The 0–4 year age group had the highest rates in both Indigenous and non-Indigenous people. Rates were lowest in older children and young adults and increased with age (Figure 12). In those recorded as Indigenous, the increase was more marked in the 25–49 year age group while, in non-Indigenous people, the rates remained low in this age group and increased at age 50 years or more.

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Figure 12. Invasive pneumococcal disease notification rates, selected Australian states,* 2003 to 2006, by age group and Indigenous status

Figure 12. Invasive pneumococcal disease 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 Indigenous to non-Indigenous rate ratios were statistically significantly greater than 1.0 in all age groups for notifications and hospitalisations. The highest rate ratios were in the age group 25–49 years (Table 13 and Table 14). Hospitalisations for pneumococcal pneumonia showed a greater disparity between Indigenous and non-Indigenous adults, and less in children (Figure 13).

Figure 13. Pneumococcal pneumonia (not coded as meningitis or septicaemia) hospitalisation rates, selected Australian states,* 2002 to 2005, by age group and Indigenous status

Figure 13. Pneumococcal pneumonia (not coded as meningitis or septicaemia) hospitalisation rates, selected Australian states, 2002 to 2005, by age group and Indigenous status

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

† Hospitalisations where the date of separation was between 1 July 2002 and 30 June 2005.

Serotype data were available for 4,851 (82%) of the total 5,941 IPD notifications. The proportion of 7-valent pneumococcal vaccine serotypes causing disease in Indigenous children in the 0–4 year age group (30%) was significantly lower than in non-Indigenous children in the same age group (81%, p<0.0001). Similarly, the proportion of 23-valent pneumococcal vaccine serotypes causing disease in Indigenous people older than 15 years was significantly lower (67%) than in non-Indigenous people in this age group (91%), p<0.0001).

During the period 2003 to 2005, there were 11 deaths recorded from IPD in the Northern Territory, Queensland, South Australia and Western Australia. Two were in persons identified as Aboriginal and Torres Strait Islander; one was in an adult over 50 years of age and the age for the other was unknown (Table 14).

Over the six-year period July 1999 to June 2005, age-adjusted hospitalisation rates for IPD remained significantly higher for Indigenous people compared with those presumed to be non-Indigenous (Figure 14), with no clear trend over time. In cases recorded as Indigenous there was a statistically significant decrease in the 0–4 year age group from 1999–2001 to 2003–2005 (p=0.0003), while in cases recorded as non-Indigenous there was also a decrease in that age group (p=0.0001) and an increase in cases aged 50 years or more (p=0.0001).

Figure 14. Invasive pneumococcal disease hospitalisation rates, selected Australian states,* 1999 to 2005, by Indigenous status

Figure 14. Invasive pneumococcal disease 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.

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Comment

The period covered by this report saw the introduction (in 2005) of universally funded pneumococcal vaccination for infants (7-valent conjugate at 2, 4, 6 months of age) and the elderly (23-valent polysaccharide from 65 years of age). These were in addition to the pre-existing programs targeting Aboriginal and Torres Strait Islander and other high-risk infants (from 2001) and Indigenous adults aged 50 years or more and younger Indigenous adults with risk factors (from 1999).

Higher rates of IPD have been consistently found in Indigenous compared with non-Indigenous Australians of all ages, the highest rates in those aged less than 5 years and more than 25 years, and particularly in central and northern Australia. Funded pneumococcal vaccination programs were targeted to Aboriginal and Torres Strait Islander people for the first 2–2 years of data presented here, the length of time varying with the dataset used, followed by between 6 months and 2 years covered by universal vaccination programs. Despite the longer period during which vaccination was funded for Indigenous people, whether during targeted or universal programs, substantially higher morbidity burdens were seen in Indigenous people. However, the Indigenous to non-Indigenous rate ratios were lowest in those age groups most directly targeted for vaccination, where the greatest benefits would be expected (i.e. 0–4 years and 50 years or more).

More detailed data have been published elsewhere, in particular annual reports of enhanced IPD surveillance.73–77 They show that the reported deaths presented above are a substantial under-estimate of deaths due to invasive pneumococcal disease, with 128 deaths recorded nationally in 2005 by that enhanced surveillance system, nine in Aboriginal or Torres Strait Islander people,77 compared with the data presented above from the AIHW mortality database, which has only nine deaths from four jurisdictions in the three-year period, two of whom were Indigenous. The enhanced surveillance data show that the disparity between Indigenous and non-Indigenous young children was eliminated following the implementation of the targeted vaccination program in 2001,77 despite suboptimal vaccination coverage.78 However, following the commencement of the universal infant program, the greater relative decrease in IPD rates in non-Indigenous children led to a re-emerging disparity between Indigenous and non-Indigenous children. Most importantly, total IPD rates are much lower than pre-vaccine levels in both Indigenous and non-Indigenous children. However, as non-vaccine type disease was and is more common in Indigenous children, a disparity between Indigenous and non-Indigenous children is difficult to eliminate.77 Conjugate vaccines active across a broader range of IPD serotypes are needed to further reduce disease in Aboriginal and Torres Strait Islander children. The results of clinical trials on two new vaccines with broader serotype coverage are awaited with interest.79,80

The impact in adults has been less clear in both Indigenous and non-Indigenous people. There have been reports of decreases in IPD in Aboriginal and Torres Strait Islander adults following vaccination programs in north Queensland81 and the Kimberley,82 but no decrease in the Northern Territory.83 Data from the first year of universal vaccination show reductions in IPD in adults, but it is not clear at this early stage whether these are attributable to adult vaccination, herd immunity from infant vaccination, or other causes.5 However, the high rates of IPD in younger Indigenous adults, together with the reported low vaccination coverage in that age group, suggest there may be potential benefits from reducing the recommended age for universal vaccination of Indigenous adults below the current 50 years. Given the limitations of the polysaccharide vaccine, including lower effectiveness against IPD,84 no proven effectiveness against other manifestations such as non-bacteraemic pneumonia,84 and concerns about hypo-responsiveness to doses after the first,85 the results of trials in adults of conjugate vaccines with broader serotype coverage are keenly anticipated.

Substantial benefits have been seen from pneumococcal vaccination of Aboriginal and Torres Strait Islander infants (since 2001), and to a lesser extent, adults (since 1999). Despite this, Indigenous people of all ages continue to suffer higher rates of pneumococcal disease compared with non-Indigenous people.