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

Haemophilus influenzae type b 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

Haemophilus influenzae is a Gram-negative bacterium which occurs in both encapsulated and unencapsulated forms. It is a commensal of the nasopharynx, especially in young children. Before Hib vaccines became available, one encapsulated serotype, type b (Hib), caused at least 95% of invasive disease due to H. influenzae in children.27,28 Prior to the introduction of Hib vaccination, the most common manifestation of invasive Hib disease was meningitis, with children aged less than 18 months most at risk.27,28 Aboriginal and Torres Strait Islander children had a particularly elevated risk of Hib meningitis, with rates among the highest recorded anywhere in the world, but rarely developed epiglottitis.29 Survivors of Hib meningitis commonly had neurological sequelae such as deafness and intellectual impairment.27,28 Epiglottitis was the other major category of infection, most often occurring in children over the age of 18 months. Other manifestations of Hib disease include cellulitis, septic arthritis, pneumonia, pericarditis, osteomyelitis and septicaemia.

Case definitions


Notifications

National definition from January 2004:10

Isolation of Haemophilus influenzae type b (Hib) from a normally sterile site where typing has been confirmed at an approved reference laboratory; or

Detection of Hib antigen in cerebrospinal fluid when other laboratory parameters are consistent with meningitis.

(See Appendix D for pre-2004 definition)

Hospitalisations and deaths

Hospitalisations and deaths were not analysed as there are no ICD-10-AM/ICD-10 codes which specify Hib as a causative organism, as opposed to Haemophilus influenzae (type unspecified).

Distribution by Indigenous status and age

Of the total 51 notifications of invasive Hib disease recorded in New South Wales, the Northern Territory, South Australia, Victoria and Western Australia over the four years between 2003 to 2006, 10 (24%) were identified as occurring in Aboriginal and Torres Strait Islander people (Table 1).

Children 0–4 years of age accounted for 22 (43%) of all the Hib notifications and, of these, seven (32%) were identified as Aboriginal and Torres Strait Islander, with a rate of 4 per 100,000 (Table 1).

The overall Indigenous to non-Indigenous notification rate ratio was 8.8:1 and statistically significantly above 1.0 overall and in both age groups, highest in the 0–4 year age group (11 per 100,000, Table 1).

Table 1. Hib notifications, 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
7
4.3
10.6||
Other
15
0.4
5 and over Indigenous
3
0.3
5.6||
Other
26
0.0
All ages Indigenous
10
0.6
8.8||
Other
41
0.1

* 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).

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Comment

The Hib immunisation program in Australia commenced in April 1993, with catch-up immunisation for children up to 5 years of age from July 1993. Until June 2000, Aboriginal and Torres Strait Islander children were scheduled to receive a different Hib vaccine (conjugated to the outer membrane of Neisseria meningitidis type C, PRP-OMP) than other children who received a vaccine conjugated to a mutant diphtheria toxin (CRM197). The OMP vaccine provides protection at an earlier age than other Hib vaccines. From June 2000, all Australian children received PRP-OMP vaccine. In November 2005, a hexavalent combination vaccine (DTP-HepB-IPV-Hib) with PRP-T Hib component became available. From that time, Aboriginal and Torres Strait Islander children in the Northern Territory, Queensland, South Australia and Western Australia continued to receive the PRP-OMP vaccine, while non-Indigenous children and Indigenous children in other jurisdictions may receive either vaccine.

Vaccination has had a striking impact on the incidence of Hib disease in the age groups targeted by immunisation programs, among both Aboriginal and Torres Strait Islander and non-Indigenous children.30 Compared with an incidence of 35–40 per 100,000 in non-Indigenous children and up to 280 per 100,000 in Indigenous children aged less than 5 years living in the Northern Territory,31 notification rates presented in this report (0.4 and 4, respectively, in 2003–2006) represent a reduction of 50– to 100-fold since vaccination was introduced.

While the number of cases decreased markedly, the proportion of total Hib disease cases occurring in Aboriginal and Torres Strait Islander people increased from around 7% before 199330 to 28% in 2000–2002.1 However, there does not appear to have been further exacerbation of this disparity during the period covered in this report as there have been slight decreases, in comparison with the previous report, in the proportion being Aboriginal and Torres Strait Islander (24%), in point estimates for the rate in Indigenous people (0.6/100,000 population/year vs 1.2) and in the Indigenous to non-Indigenous rate ratio (8.8:1 vs 9.7:1).

A similar pattern of substantially reduced incidence but widening disparity between rates in Indigenous and non-Indigenous populations was also seen in the United States32 and New Zealand.33 The disparity appears to have reduced in more recent data.32,34

Higher rates of Hib disease have been associated with crowded living conditions and consequent high levels of Hib colonisation in the nasopharynx. While there is no evidence of low vaccination coverage,18,31,34,35 it cannot be ruled out in some local areas. Sustained high coverage with PRP-OMP vaccine in areas of high incidence and improvements in environmental living conditions are needed to eliminate this disparity.

Hib vaccination has been very successful in preventing disease in Aboriginal and Torres Strait Islander children. The number of Hib cases continues to decline; however, Aboriginal and Torres Strait Islander people still record rates nearly nine times higher than people presumed to be non-Indigenous. This difference is greatest in children 0–4 years of age.