Pertussis (whooping cough) is caused by Bordetella pertussis, a Gram-negative bacterium.3 It is characterised by an insidious onset of symptoms of minor upper respiratory infection, minimal fever and cough which becomes paroxysmal in 1–2 weeks. During the paroxysmal stage, the cough is most severe when the characteristic whoop occurs. Complications include suppurative otitis media, pneumonia, pulmonary hypertension, acute pertussis encephalopathy and nutritional deficiencies due to repeated vomiting.3

Relevant vaccine history

1942

  • Pertussis vaccination programs started in most states/territories using 3 doses of whole-cell pertussis vaccine (Pw).

1975

  • First national vaccination schedule recommended and funded 4 DTPw* doses for infants at 3, 4, 5 and 18 months of age.

1978

  • Fourth dose removed from schedule (reinstated 1985).

1994

  • Fifth dose added at 4–5 years of age.

1999

  • DTPa recommended and funded for all 5 childhood DTP doses.

2003

  • 18-month booster replaced by adolescent dose; the eligible age group varied in different jurisdictions.

2008–2012

  • dTpa funded temporarily by various states and territories for parents/contacts of infants under cocoon strategy during an epidemic. Program timing and eligibility criteria differed between jurisdictions.

Key points

Pertussis continues to circulate, causing periodic epidemics in adolescents and adults and transmission to infants who are most vulnerable to severe disease. There is a disproportionate impact on Aboriginal and Torres Strait Islander infants. Timely administration of infant doses is very important. The first dose can now be given at 6 weeks of age.

* DTPw: diphtheria, tetanus and pertussis (whole-cell)

† DTPa: diphtheria, tetanus and pertussis (acellular)

‡ dTpa: diphtheria, tetanus and pertussis (acellular), reduced antigen content

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Disease trends

Hospitalisation data (for the Northern Territory, Queensland, South Australia and Western Australia) are presented for the period July 1999 to June 2010. The 10-year trend shows a cyclical pattern of epidemics every 3–5 years. However, there has been an overall upward trend from baseline, especially in Aboriginal and Torres Strait Islander people (Figure 2.8.1).

Figure 2.8.1: Pertussis hospitalisation rates and 95% confidence intervals, selected Australian states,* 1999 to 2010, by Indigenous status

Figure 2.8.1: is a line chart showing the Pertussis hospitalisation rates and 95% confidence intervals, selected Australian states, 1999 to 2010. A link to a text description follows.

* Jurisdictions with satisfactory data quality over the whole time period; see Appendix A (New South Wales, Queensland, South Australia, Western Australia).

† Hospitalisations where the date of separation was between 1 July 1999 and 30 June 2010. Rates are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2006.

Text description of Figure 2.8.1 (TXT 1 KB)

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Hospitalisation data are presented for six jurisdictions (all except Tasmania and the Australian Capital Territory) by financial year for the period July 2005 to June 2010. Data for notifications are not presented due to the low level of completeness of the Indigenous status field in notification records.

A total of 3,772 hospitalisations for pertussis were recorded during this reporting period, of which 362 (9.6%) were reported in Aboriginal and Torres Strait Islander people (Table 2.8.1). The rates were higher in Aboriginal and Torres Strait Islander people than in other people across all age groups. The highest hospitalisation rates occurred in the youngest age group (0–4 years) especially in Aboriginal and Torres Strait Islander children (93.2 per 100,000). The overall Indigenous to non-Indigenous rate ratio was 2.9:1, with the highest ratio (3.3:1) in the 0–4 years and 15–24 years age groups.

Table 2.8.1: Pertussis hospitalisations, selected Australian states, 2005 to 2010, by age group and Indigenous status
Age group
(years)
Indigenous status Hospitalisations* (2005–2010)
n Rate Rate ratio

* Hospitalisations (New South Wales, Northern Territory, Queensland, South Australia, Victoria, Western Australia only) where the date of separation was between 1 July 2005 and 30 June 2010.

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

‡ Includes cases with age unknown. Rates for all ages combined are age-standardised to the Australian Bureau of Statistics Australian population estimates for 2006.

§ Indicates statistically significant, 95% confidence intervals do not overlap 1.0.

0–4
Indigenous
292
93.2
3.3§
Other
1,748
28.4
5–14
Indigenous
13
2.1
1.8§
Other
149
1.2
15–24
Indigenous
10
2.0
3.3§
Other
83
0.6
25–49
Indigenous
25
3.1
2.7§
Other
420
1.2
>50
Indigenous
22
7.3
2.2§
Other
1,010
3.3
All ages
Indigenous
362
10.0
2.9§
Other
3,410
3.5

Those ≥50 years of age have the second highest hospitalisation rates. This pattern is similar for both Aboriginal and Torres Strait Islander and other people.

There were 10 deaths reported from the five jurisdictions (New South Wales, the Northern Territory, Queensland, South Australia and Western Australia) for the period 2006–2010 with pertussis as the underlying cause and 17 deaths with pertussis as either the underlying or a contributing cause. There were 1–4 deaths reported in Aboriginal and Torres Strait Islander people with pertussis as either the underlying or a contributing cause (the ABS provides ranges when absolute numbers of deaths are low).

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Comment

Pertussis is the least well controlled of all vaccine preventable diseases with long-standing, well-established vaccination programs. It has the highest notification rates in all age groups for the total Australian population, and higher hospitalisation rates than most other vaccine preventable diseases. Epidemics continue to occur which affect both Aboriginal and Torres Strait Islander and other people, although Aboriginal and Torres Strait Islander people have higher hospitalisation rates. Epidemics result in higher rates of hospitalisation across all age groups, but of particular concern are the rates for infants <1 year of age.

The latest pertussis epidemic commenced midway through the second half of 2008 and spread across all Australian jurisdictions. A recent resurgence in pertussis has been observed in many countries in North America and Europe.54-56 Increases have been most marked in adolescents and adults in whom the disease is less severe, but infant deaths have also occurred.55 The most important factors contributing to increased notifications are thought to be improved diagnosis and surveillance, increased awareness of pertussis in adolescents and adults, lower effectiveness of newer (acellular) vaccines,57 and pathogen strain shifts.58 The higher sensitivity of molecular tests (PCR) compared to serology and culture, which were the only tests widely available several years ago, contributes to increased diagnosis and reporting. There was also an increase in presentation and testing associated with concern about pandemic influenza in 2009. Research in the Netherlands noted that an increase in notifications, a changing age demographic towards older age groups and increasing disease severity were associated with changes in circulating pertussis strains which expressed increased pertussis toxin production.58

In order to protect those who are most vulnerable to severe disease, from 2008 to 2012 DTPa vaccination was funded by various states and territories for parents/contacts of infants under the ‘cocoon’ strategy. Parents are also now encouraged to have the infant’s first vaccination given at 6 weeks of age, instead of the usual 2 months. Timely vaccination of the 4- and 6-month doses is also very important.