Vaccine Preventable Diseases and Vaccination Coverage in Australia, 2003 to 2005

Q fever

Disclaimer: This is the fourth report on vaccine preventable disease and vaccination coverage in Australia, and is 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 31, June 2007.

Page last updated: 20 July 2007

Q fever is a zoonotic disease caused by Coxiella burnetii. It infects both wild and domestic animals and their ticks, with cattle, sheep and goats the main source of human infection. Infected animals shed C. burnetii into the environment through their products of conception (in especially high numbers) but also in their urine, milk and faeces. Transmission to humans is via inhalation of infected droplets or dust. Q fever can be acute or chronic,194 and there is increasing acceptance of an association with long-term sequelae including post Q fever fatigue syndrome.195–197 However, in many instances infection is asymptomatic. Symptoms of the acute illness resemble those of influenza but can be complicated by encephalitis, pneumonitis, hepatitis, myocarditis and pericarditis. Chronic Q fever, which may occur years after infection, is most often characterised by endocarditis.198

A vaccine against Q fever, Q-VAX® (CSL Limited) was licensed in Australia in 1989 and, following successful Australian trials,199–201 vaccination programs have been operating in most large abattoirs since the mid 1990s.202 To improve vaccination coverage in the wider at-risk population, the Commonwealth Government funded the National Q fever Management Program (NQFMP).203 The program was funded and delivered in two phases. Phase one targeted the meat and livestock industry, promoting screening and vaccination services to abattoir workers, workers contracted to abattoirs and sheep shearers ($10.6 million funding over three years). Phase two targeted sheep, dairy and beef cattle farmers, their employees and unpaid family members working on farms ($8 million funding over three years). The program was implemented in all states and the Australian Capital Territory during 2001–2002, with vaccination activity peaking in 2002.

Case definitions

See Appendix 6 for pre 2004 definition

National definition from January 2004:11

Confirmed cases require either laboratory definitive evidence or laboratory suggestive evidence and clinical evidence.

a) Laboratory definitive evidence

  • Detection of Coxiella burnetii by nucleic acid testing; or
  • Seroconversion or significant increase in antibody level to Phase II antigens in paired sera tested in parallel in absence of recent Q fever vaccination; or
  • Detection of C. burnetii by culture.

b) Laboratory suggestive evidence

  • Detection of specific IgM in the absence of recent Q fever vaccination.

c) Clinical evidence

  • A clinically compatible disease.

Hospitalisations and deaths

The ICD-9 code 083.0 (for historical data) and ICD-10 code A78 were used to identify hospitalisations and deaths.

Secular trends

In the three year review period there were 1,375 notified cases of Q fever (average annual rate of 2.3 per 100,000) and 652 hospitalisations with the ICD-10 code A78 for Q fever (average annual rate 1.1 per 100,000). Both notification and hospitalisation rates declined over the review period, following a peak in 2002, to the lowest levels on record in the most recent year reviewed (1.7 and 0.8 per 100,000, respectively). There was a median of 36 (range 20–79) notifications and 17 hospitalisations (range 9–31) per month. The considerable monthly variation did not appear to be seasonal.

Figure 34. Q fever notifications and hospitalisations, Australia, 1993 to 2005,* by month of diagnosis or admission

Figure 34. Q  fever notifications and hospitalisations, Australia, 1993 to 2005, by month  of diagnosis or admission

* Notifications where the month of diagnosis was between January 1993 and December 2005;
hospitalisations where the month of admission was between 1 July 1993 and 30 June 2005.

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Severe morbidity and mortality

In the three year review period, hospital separations for Q fever accounted for 3,807 hospital bed days. The median length of stay (LOS) overall was 4 days but, in adults, the LOS increased with age (Table 17). Of the 652 hospitalisations, 502 (77%) had Q fever recorded as the principal diagnosis. However, only 62 (54%) of the 115 hospitalisations in the 60 years and over age group were recorded as the principal diagnosis.

In the National Mortality database, four deaths were recorded with an underlying cause of death coded as Q fever in 2003–2004. All were in adults aged at least 25 years. Three were female and one was male. There were two deaths in notified cases reported to NNDSS between 2003 and 2005.

Table 17. Q fever notifications, hospitalisations and deaths, Australia, 2002 to 2005,* by age group

Age group
(years)
Notifications 3 years
(2003–2005)
Hospitalisations 3 years
(July 2002–June 2005)
LOS per admission
(days)
Deaths 2 years
(2003–2004)
  n Rate n (§) Rate (§) Median (§) n Rate
0–4
5
0.1
3
(2)
0.1
(0.1)
5.0 (3.0)
0
5–14
39
0.5
14
(13)
0.2
(0.2)
3.0 (3.0)
0
15–24
173
2.1
88
(78)
1.1
(1.0)
2.0 (3.0)
0
25–59
953
3.2
432
(347)
1.5
(1.2)
4.0 (4.0)
3
0.02
60+
205
2.0
115
(62)
1.1
(0.6)
7.0 (7.0)
1
0.01
All ages
1,375
2.3
652
(502)
1.1
(0.8)
4.0 (4.0)
4
0.01

* Notifications where the month of diagnosis was between January 2003 and December 2005; hospitalisations where the month of separation was between 1 July 2002 and 30 June 2005; deaths where the death was recorded in 2003 or 2004.

† LOS = length of stay in hospital.

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

§ Principal diagnosis (hospitalisations).

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Age and sex distribution

The male to female ratio for both notifications and hospitalisations has generally been decreasing over time since the early 1990s, but remained relatively constant over the three year review period at 3.3:1 and 3.8:1, respectively.

As in previous years, adult males aged 15–39 and 40–64 years had the highest notification and hospitalisation rates (Figure 35). In the 1990s males aged 15–39 years had the highest rates, but, since then, rates have been highest in males aged 40–64 years.

All age/sex groups showed a decline in notification and hospitalisation rates over the three year review period except the 65 years and over age group which had a peak in hospitalisations in 2003/2004. This oldest age group also contributed proportionally more hospitalisations (13%) than notifications (8%) during the review period.

Figure 35. Q fever notification rates, Australia, 1993 to 2005,* by age group and sex

Figure 35. Q  fever notification rates, Australia,  1993 to 2005, by age group and sex

* Notifications where the date of diagnosis was between 1 January 1993 and 31 December 2005.

Figure 36. Q fever hospitalisation rates, Australia, 1993 to 2005,* by age group and sex

Figure 36. Q  fever hospitalisation rates, Australia,  1993 to 2005, by age group and sex

* Hospitalisations where date of separation was between 1 July 1993 and 30 June 2005.

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Geographical distribution

As in previous years, notification and hospitalisation rates were highest in Queensland followed by New South Wales (Appendix 2 and Appendix 3). Together, these two states contributed 86% of the notifications and 83% of the hospitalisations for Q fever over the review period.

Consistent with national trends, notification rates in both of these states declined to record low levels over the three years reviewed with only a few outbreaks reported. There were six small clusters of Q fever cases reported nationally in 2003 with five of these in Queensland.13 In 2004, a cluster of ten cases associated with a shearing team was reported in New South Wales.204 Rates in other jurisdictions remained low over the review period. The exceptions were: South Australia, which experienced an outbreak associated with a sheep saleyard in late 2004;12 and the Northern Territory which reported three cases in each of 2004 and 2005 when prior to 2004 there had only been two cases in total reported since 1991. The three cases in 2004 were unrelated. One was a foreign national working on a cattle boat205 and two cases were from Central Australia, one of whom died.206

Hospitalisation rates tended to follow the same pattern as notifications, except that there were few hospitalisations reported from South Australia during the 2004 outbreak.

Vaccination status

Vaccination status is requested on all Q fever notifications but was recorded only for 903 (66%) of the 1,375 notified cases in 2003–2005. Fourteen cases were recorded as being fully vaccinated, six of whom had their vaccination status validated by written records.

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Comment

Q fever notification and hospitalisation rates declined to record low levels during the review period. The decline follows an increase in screening and vaccination activity associated with the NQFMP; phase one was fully implemented by the end of 2002 while phase two activity was predominantly in 2003. These data are supported by a decline in claims for workers’ compensation for Q fever over this period.207 It appears, therefore, that the NQFMP has contributed to a reduction in the burden of Q fever in Australia, although it is difficult to estimate the contribution of non-program factors such as an improvement in drought conditions (droughts promote airborne dissemination) and variation in livestock slaughtering. However, the reductions are most noticeable in young adult males who were the main target in phase one of the program.

Despite these promising findings, longer term and enhanced surveillance is required to fully evaluate the impact of the NQFMP. Most jurisdictions completed the program by 2005, but Victoria and South Australia continued until 30 June 2006, and Queensland will continue until 30 June 2007.12 Ongoing surveillance is, therefore, required to detect variations between states and following completion of the program. Although there have been recent publications using enhanced state notification data to document trends in Q fever notifications by occupation,208–211 there is a need for enhanced data at a national level, including the occupation of cases and complete information about their vaccination status. Such data will help to better determine the targeted impact of the NQFMP, further understand the epidemiology of Q fever, and identify the most appropriate vaccination strategies for the future.

Australia is the only country to have implemented a vaccination program of any kind, even though Q fever has been found world-wide (except in New Zealand).195,212,213 Large outbreaks continue to be reported from many countries.214–216 However, annual rates in North America, the United Kingdom and most of Europe are low compared with Australia. In 2000–2004, an average of only 51 cases was reported each year in the USA217 and, since 2000, the number of reported cases in the UK has declined annually to less than 50 sporadic cases each year.218 The variation between countries may be the result of true epidemiological differences, but could also be due to differences in awareness, surveillance, or diagnostic methods.

In summary, there appears to be an impact of the NQFMP on the burden of Q fever in Australia, but confounding factors are difficult to exclude. Q fever surveillance data must, therefore, be monitored over a longer period of time to fully assess the impact of the program. In addition, more complete national surveillance data on the occupation and vaccination status of cases is recommended.

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