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

Rubella

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

Rubella is caused by the rubella virus (family togaviridae). It is usually a mild, febrile, viral disease characterised by a rash, conjunctivitis, coryza, postauricular and suboccipital lymphadenopathy, and nausea, but may be subclinical in up to 50% of cases. Arthralgia and arthritis may also occur, particularly in women. More severe disease manifestations, such as encephalitis, haemorrhage and Guillain-Barré syndrome, may also rarely occur. Rubella is important because of its ability to produce death or abnormalities in the developing fetus (congenital rubella syndrome (CRS)) when acquired in early pregnancy.242

Case definition

See Appendix 6 for pre 2004 definition

National definition from January 2004:11

A confirmed case requires laboratory definitive evidence. A probable case requires clinical evidence and either laboratory suggestive evidence or an epidemiological link to a laboratory-confirmed case.

a) Laboratory definitive evidence

  • Isolation of rubella virus; or
  • Detection of rubella virus by nucleic acid testing; or
  • IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to rubella virus in the absence of recent rubella vaccination in paired sera tested in parallel; or
  • Detection of rubella-specific IgM antibody in the absence of recent rubella vaccination (must be confirmed in a reference laboratory in pregnant women).

b) Laboratory suggestive evidence

  • In a pregnant patient, the detection of rubella-specific IgM antibody that has not been confirmed in a reference laboratory, in the absence of recent rubella vaccination.

c) Clinical evidence

  • A generalised maculopapular rash and fever, and one or more of: arthralgia/arthritis or lymphadenopathy or conjunctivitis

Hospitalisations and deaths

The ICD-10-AM/ICD-10 code B06 (rubella [German measles]) was used to identify hospitalisation and deaths.

Congenital rubella cases were not included in this report. Reviews of congenital rubella cases recorded by the Australian Paediatric Surveillance Unit between 1993 and 2004 are available elsewhere.243,244

Secular trends

Between January 2003 and December 2005, there were 116 notified cases of rubella, an average annual notification rate of 0.2 per 100,000 (Table 20). There was a continuing and marked decline in the number of notifications with a more than sevenfold decrease between the current and previous three year period (2000–2002) when there were 844 cases notified. There were 54 notifications in 2003 (0.27 per 100,000) and 31 notifications (0.15 per 100,000) in 2004 and again in 2005. Between July 2002 and June 2005, 44 hospitalisations were coded as being due to rubella (an average annual rate of 0.07 per 100,000). Hospitalisations coded as rubella fell to historical lows, with 21 separations in 2002/2003, 18 in 2003/2004 and only five in 2004/2005. The current low incidence of rubella now means that the previously discernible spring peaks3 in rubella activity are no longer observed (Figure 41).

Figure 41. Rubella notifications and hospitalisations, Australia, 1993 to 2005,* by month of diagnosis or admission

Figure 41. Rubella  notifications and hospitalisations, Australia, 1993 to 2005, by month of  diagnosis or admission

Note: varying scales between notifications and hospitalisations.

* 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 period 2002/2003–2004/2005, 131 hospital bed days (average 44 per year) were recorded for patients with an ICD-10-AM code for rubella. In 2004/2005, there were only 10 hospital bed days coded with rubella. Of the hospital separations, 75% had a principal diagnosis of rubella (average annual rate 0.06 per 100,000). The median length of stay in hospital was two days, but increased with age (Table 20). In 2003 to 2004, there were no deaths with rubella recorded as the underlying cause.

Complications arising from rubella infection were recorded for five (11%) hospitalisations (Table 21). Only one case with complications was recorded in a child. Neither of the two cases with neurological complications was also coded as having other complications of rubella.

Table 20. Rubella 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
12
0.32
21
(17)
0.55
(0.45)
1.0 (1.0)
0
0
5–14
2
0.02
3
(2)
0.04
(0.02)
n.p.
0
0
15–24
43
0.52
7
(6)
0.09
(0.07)
2.0 (2.0)
0
0
25–59
56
0.19
10
(6)
0.03
(0.02)
3.0 (1.0)
0
0
60+
3
0.03
3
(2)
0.03
(0.02)
n.p.
0
0
All ages
116
0.19
44
(33)
0.07
(0.06)
2.0 (1.0)
0
0

* 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).

n.p. Not published due to small cell sizes.

Table 21. Indicators of severe morbidity* for hospitalised cases of rubella

Age group
(years)
Complication neurological Complication other
  n % total n % total
0–4
0
0.0
1
4.8
5–14
0
0.0
0
0.0
15–24
0
0.0
0
0.0
25–59
1
10.0
0
0.0
60+
1
33.3
2
66.7
All ages
2
4.5
3
6.8

* Measured using National Hospital Morbidity data where the month of hospital separation was between 1 July 2002 and 30 June 2005.

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Age and sex distribution

For the three year review period, notification rates were highest in the 20–24 year old age group, who accounted for nearly a quarter (24%) of cases (average annual rate 0.67 per 100,000). Within this age group, males predominated (male:female ration 3.5:1) and it was the only group where the notification rate was over one per 100,000. Together, the 25–29 year and 30–34 year age groups accounted for a further 31% of rubella notifications, with 18 notifications in each of these groups over the three year period (data not shown). The progressive increase seen in the median age of notified cases since the Measles Control Campaign (MCC) in 1998 has plateaued in the last three years, with the median age for notified cases of 25 years in each year 2003–2005 (up from 22 years in 2002.)

In 2003–2005, the male to female ratio for notifications was 1.3:1. This ratio disguises some variation by age group, with males predominating both in infants 0–4 years (10/12 cases) and in those aged over 20 years, but more female than male cases in the 15–19 year age group (11/15 cases). However, due to the low number of cases, these differences should be interpreted with caution.

For the three years combined, 2002/2003–2004/2005, children aged 0–4 years continued to have the highest hospitalisation rates (average annual rate 0.6 per 100,000). Whilst two thirds of hospitalisations in this group were males, the overall male to female ratio for hospitalisations was identical to the ratio for notifications (1.3:1). Whilst just over half of the hospitalisations were in infants too young to be vaccinated (11/21 aged under one year), no notifications were received for infants under one year of age in 2003–2005.

There were 40 notified cases of rubella in women of child bearing age (15–44 years) in 2003–2005, an average annual rate of 0.3 per 100,000. This rate has been declining each year since the outbreak in 1995 (rate 16.0 per 100,000) and is a notable decline from the previous reporting period 2001–2002 when the rate was 1.1 per 100,000. Within this age range, and indeed for any female age group, highest rates were reported in those aged 15–19 years (0.6 per 100,000).

Figure 42. Rubella notification rates, Australia, 1999 to 2005,* by age group, sex and year of diagnosis

Figure 42.  Rubella  notification rates, Australia,  1999 to 2005, by age group, sex and year of diagnosis

* Notifications where date of diagnosis was between 1 January 1999 and 31 December 2005.

Figure 43. Rubella hospitalisation rates, Australia, 1999/2000 to 2004/2005,* by age group, sex and year of separation

Figure 43. Rubella  hospitalisation rates, Australia, 1999/2000 to 2004/2005,  by age group, sex and year of separation

* Hospitalisations where date of separation was between 1 July 1999 and 30 June 2005.

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Geographical distribution

Most of the notifications received in 2003–2005 were from New South Wales (n=50; rate 0.25 per 100,000) or Queensland (n=43; rate 0.37 per 100,000). In both states, notifications were highest in 2003, following a peak in rubella activity in Queensland in 2002 which was associated with two cases of locally acquired congenital rubella syndrome, and then declined.

No notifications of rubella were received in the Northern Territory or the Australian Capital Territory during 2003–2005. Very low numbers of cases were reported sporadically in Victoria, South Australia and Tasmania (rates of 0.07 per 100,000 or less.) In Western Australia, 12 cases were reported through the period (0.2 per 100,000) (Appendix 2).

Four notifications, all in persons aged 18–36 years, were recorded on NNDSS as imported cases (i.e. acquired whilst overseas).

Hospitalisation rates varied over time and between states and territories (Appendix 3). However, there were too few cases in each jurisdiction to identify any trends.

Vaccination status

Vaccination status for rubella cases is to be recorded on NNDSS for women of child bearing age (15–45 years). Whilst the vaccination status field was completed for all 40 cases, it was categorised as “unknown” in about one third of these (35%). Most women with known vaccination status were unvaccinated (16/26; 62%). Whilst five women reported being fully vaccinated against rubella (i.e. two doses), this was not validated by written records. Vaccination status was confirmed in three of five women who reported partial vaccination (i.e. one dose).

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Comment

Rubella notification and hospitalisation rates continue to decline and, in the most recent year reviewed, were the lowest on record. The adoption of a more specific national case definition in 2004 may have in part contributed to the ongoing decline in notifications. Hospitalisation data reported here suggest that either infants too young to be immunised are still at some (albeit small) risk of rubella in Australia or that coding errors or misdiagnosis are more likely to occur in paediatric age groups. There is no doubt that rubella control is a great immunisation success story in Australia but what challenges remain?

Notification data suggest that there remain vulnerable groups within the Australian population, particularly young males who missed out on both school based immunisation programs and natural infection.245 The Queensland rubella ‘outbreak’ of 2001/2002 clearly demonstrated that there are sufficient pockets of susceptibility to rubella within the Australian population to maintain rubella circulation amongst vulnerable individuals for some time and, unfortunately in this context, the risk of locally acquired CRS remains.246,247 Young women who have migrated to Australia may also be vulnerable due to lack of rubella vaccination programs in their countries of origin; in the last two years, six imported CRS cases were notified to the APSU.243,244 Two recent studies of rubella serology records from women’s hospitals in Melbourne and Sydney confirm that overseas born women, particularly from Asia but also from South America and sub-Saharan Africa, are more likely to be non-immune to rubella than other Australian women.248,249 Also of concern, a study of antenatal screening records identified that rural and remote Indigenous women in the Northern Territory have low rates of rubella immunity and, thus, remain susceptible to rubella.250 Antenatal rubella screening and post-natal vaccination, and rubella programs targeting women in these risk groups, will be important components of ongoing rubella control.

Those travelling within the Western Pacific region (and internationally) are at risk of rubella exposure. In 2005, 117 countries, covering 26% of the international birth cohort, were using rubella vaccines in their national immunisation programs.251 Although very few cases on NNDSS were identified as imported cases (n=4), importation status was poorly completed on NNDSS (66% of records had this field missing). WHO received 28,659 notifications of rubella from the Western Pacific Region in 2005. This is a gross underestimate of the disease burden given that many cases are asymptomatic and many countries within the region do not have rubella surveillance or rubella vaccination programs. Rubella outbreaks have been documented in recent years in Tonga and Samoa, and these outbreaks were associated with high rates of rubella encephalitis.252,253 The major regional focus of the Expanded Program on Immunization has been measles control and hepatitis B immunisation. With the increasingly successful achievements of the former target comes the opportunity for rubella programs, which require either targeting of women of child bearing age or sustained high coverage rates of the population. Guidelines to assist countries in assessing the appropriateness of adding rubella control strategies have recently been prepared by the WHO Western Pacific Regional Office. An assessment of local epidemiology, proper surveillance and coverage levels and an ability to meet and sustain the cost of MR vaccine over measles vaccine are critical.252,253

The data reviewed here suggest that Australia may be close to elimination of locally acquired rubella. In this respect, the recent elimination of rubella in the USA254 and the European plan to eliminate rubella by 2010255 will serve as good examples of possible ways forward. The United States declaration of rubella elimination could only occur in the context of a Pan American regional approach, in which successful mass immunisation campaigns, using the ’catch-up, keep-up and follow-up’ strategies, achieved high population immunity and low disease incidence in neighbouring countries such as Mexico.256 Similar to US requirements, Australia might consider targeted immunisation campaigns for immigrants from low prevalence countries. Whilst Australia already conducts measles genotyping, which provides molecular evidence that there is no indigenous strain of measles circulating, rubella genotyping is not performed. Internationally, the standardisation of nomenclature and genotyping methodology for rubella are continuing to be developed and, at this time, genotyping of rubella has not been performed in Australia.257–259 Despite its continuing development, rubella genotyping has proven a critical tool in declaring the absence of local rubella circulation in the US.260 In Australia, it is increasingly important that suspected rubella cases have specimens collected for PCR which, if positive, can be referred for genotyping.

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