Delivering a Healthy WA
Disease WAtch

Ongoing pertussis epidemic in Western Australia

Western Australia is in the midst of a pertussis (whooping cough) epidemic that commenced in mid-2011.  It follows the period from 2005–2010, in which WA had the lowest pertussis notification rates in Australia.

During the same period, other states and territories experienced relatively sustained epidemic activity, in contrast to the generally recognised pattern of 3–4 yearly epidemics. Hence, with its last epidemic year in 2004, WA has been well overdue for a pertussis epidemic, as was recognised in a previous Disease WAtch article. 1

Figure 1 shows that both nationally—and to a lesser extent in WA—there has been a stepwise increase in pertussis notification rates over the past few years, despite high vaccine coverage in young children. This suggests a re-setting of baseline levels of activity in the community, with relatively more disease observed in older children and adults. Similar patterns have been observed in other developed countries. The reasons for this are thought to include waning vaccine-induced immunity; better awareness of the disease; increased testing, including greater availability of more sensitive PCR diagnostic tests; improved reporting and surveillance; and changes in the organism itself. It is also thought that acellular pertussis vaccine, introduced in Australia in 1999, may not confer as long-lasting immunity as that provided by the whole cell vaccines used previously.

Figure 1 – Pertussis notification rates for Western Australia and Australia, 1991–2011

Line graph showing a large rise in number of notifications in WA and Australia, in the last few years.

There was a record 4015 pertussis notifications in Western Australia during 2011, almost double the number recorded in the 2004 epidemic year. The latest epidemic began noticeably in July 2011.  From then notifications increased steeply to a monthly peak of 766 cases in November 2011, as shown in Figure 2. Notifications stabilised around this high level through to January 2012, with hopeful signs of a decline in February (data for February were incomplete at the time of writing).

Figure 2 – Number of pertussis notifications in WA by month, January 2010–February 2012*

Column graph showing that the rise in pertussis numbers has been particularly acute between July 2011 to Jan 2012.

*Note: Data for February 2012 were incomplete at the time of writing

Figure 3 shows the number of cases and notification rate by age for all cases of pertussis notified in WA in 2011. The highest notification rates were in children of primary school age, with the lowest rates in teenagers and young adults, probably reflecting the benefits of the Year 7 booster dose of pertussis vaccine. Notification rates then increased again in older adults, being highest in those aged 35–44 years. Within the primary school age range, risk increased stepwise from age 5 through to age 11 years, indicating progressive waning of protection following the pre-school booster dose of pertussis vaccine, generally given at age 4 years.

Pertussis in school-aged children and adults poses a risk to infants who live in the same households, and who are most vulnerable to the complications of pertussis. Hospitalisation rates for pertussis are highest in children under 1 year of age, especially those younger than 6 months who have not completed their primary course of pertussis vaccination. In recent years, around 50% of children under 1 year of age who have been diagnosed with pertussis have been hospitalised—amounting to 56 cases in 2011. The rate of hospitalisation declines to almost nil in children aged 2 years and above. One death from pertussis was reported in each of 2008, 2009, 2010 and 2011 in WA; all were children aged 2 months or younger. 

Figure 3 – Number and rate of pertussis notifications in WA by age group, 2011

Column graph showing the highest notification rates were in children of primary school age, with the lowest rates in teenagers and young adults, probably reflecting the benefits of the Year 7 booster dose of pertussis vaccine.

Conclusion

Despite relatively high vaccination coverage, pertussis notification rates have increased both nationally and in WA in recent years. An epidemic of pertussis commenced around July 2011 in WA, and is ongoing, with the number and rate of notifications far exceeding levels recorded previously.  Whilst notification rates are currently highest in primary school aged children, attributed to waning of vaccine-induced immunity, the impact of the disease remains greatest in infants under 1 year of age, with about 50% of these cases requiring hospitalisation.

Vaccination remains the most effective intervention to reduce the burden of pertussis, notwithstanding the fact that it provides imperfect protection. In addition to the routine childhood schedule, as a consequence of increasing rates in older age groups, the Australian National Health and Medical Research Council recommends that a booster dose of diphtheria-tetanus-pertussis vaccine (dTpa)  be offered to the following adult groups2:

  • parents planning a pregnancy, or both parents as soon as possible after delivery of an infant
  • other household members and carers, including grandparents
  • those working with young children, such as child-care workers
  • health care workers
  • any adult expressing an interest in receiving a diphtheria-tetanus booster.

Adult pertussis vaccines must be provided by private prescription, although the WA Department of Health is funding the vaccine for parents, grand-parents and other household carers of babies less than 6 months of age in order to protect newborns during the current epidemic. This program will be reviewed at the end of June 2012.

As indicated in the box below, the clinical and public health management of pertussis is directed toward early identification and treatment of cases; exclusion of infectious individuals from settings where they may transmit disease, in particular to vulnerable infants; and targeted vaccination and antibiotic prophylaxis for exposed infants and household, healthcare and childcare contacts who may expose vulnerable infants.3,4

Summary of clinical and public health management for cases of pertussis

(For further details, see: Pertussis information for GPs and other healthcare providers3 and/or National guidelines for the public health management of pertussis.4

Case management

  1. Verify diagnosis: PCR on a nasopharyngeal (aspirate or swab) specimen preferred in cases presenting within 21 days of onset. Dry nose or throat swabs are acceptable. Serum IgA testing (acute and convalescent) is an option, particularly for late presenting cases.
  2. Antibiotic treatment: Commence prior to result if reasonable suspicion that patient has pertussis, and if less than 21 days since onset of cough. Clarithromycin, azithromycin, erythromycin or trimethoprim/sulfamethoxazole are recommended. For dosage see Therapeutic guidelines: antibiotic.5
  3. Exclusion: From work, school, childcare and other settings with young children for 21 days following cough onset or until 5 days of treatment has been completed.
  4. Notify: Communicable Disease Control Directorate (Perth metropolitan area) or your rural Public Health Unit of confirmed cases. Public Health Units will assist with contact management if appropriate.

Contact management:

  1. Ensure that other children in a household or childcare setting are up-to-date with recommended pertussis vaccines.
  2. Antibiotic prophylaxis is recommended only for high-risk contacts or in high-risk settings, including: households and child-care settings with young children who have not had 3 doses of pertussis vaccine; women in their last month of pregnancy; and infants, staff and parents in maternity wards and neonatal nurseries. Prophylaxis is not recommended in settings such as primary schools, high schools, tertiary education facilities or work-places.
  3. Exclusion: Only for child contacts who attend childcare or pre-school and who have received less than 3 doses of pertussis vaccine, for 14 days after last exposure to the case, or until they have completed 5 days of an appropriate antibiotic.

References

1. Communicable Disease Control Directorate. Disease update: pertussis in Western Australia. Disease WAtch. 2010; 14: 2-5

2. National Health and Medical Research Council. Australian immunisation handbook, 9th ed. Canberra: Australian Government Department of Health and Ageing, 2008.

3. Communicable Disease Control Directorate. Pertussis—information for GPs and other healthcare providers on clinical and public health management. March 2010.

4. Department of Health, WA. National guidelines for the public health management of pertussis. OD 0129/08, 2008.

5. Antibiotic Expert Group. Therapeutic guidelines: antibiotic. Version 14. Melbourne: Therapeutic Guidelines Limited, 2010.

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