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

Mumps

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

Mumps is an acute viral disease caused by a paramyxovirus. The disease is characterised by fever, swelling and tenderness of one or more salivary glands, most commonly the parotid glands. Symptomatic aseptic meningitis occurs in up to 10% of cases. Other potentially serious complications are less frequent and include pancreatitis, orchitis and encephalitis.44

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, or clinical evidence and an epidemiological link to a laboratory-confirmed case.

a) Laboratory definitive evidence

  • Isolation of mumps virus; or
  • Detection of mumps virus by nucleic acid testing; or
  • IgG seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to mumps virus in the absence of recent vaccination

b) Laboratory suggestive evidence

  • Detection of mumps-specific IgM antibody in the absence of recent vaccination.

c) Clinical evidence

A clinically compatible illness characterised by swelling of the parotid or salivary glands lasting two days or more without other apparent cause.

Hospitalisations and deaths

The ICD-10-AM/ICD-10 code B26 (mumps) was used to identify hospitalisations and deaths.

Secular trends

During the three years from January 2003 to December 2005, there were 419 notifications of mumps (an average annual notification rate of 0.69 per 100,000) (Table 11). Since 2002, when mumps notifications were the lowest on record, mumps cases have increased, and in 2005, reached the highest level since notification began in 1993, with a rate of 1.18 per 100,000 (Figure 22). Monthly numbers of notifications varied considerably, with a median of 9.5 (range 2–32) notifications per month. Notifications peaked in June 2005, with 32 notifications, and were above 10 per month between November 2004 and November 2005.

From July 2002 to June 2005, there were 138 hospitalisations coded as due to mumps (average annual rate of 0.23 per 100,000) (Table 11) with a median of 3.5 admissions per month (range 0–7). Hospitalisation rates were stable over the period, in contrast with the increase in notification rates (Figure 22). However, the hospitalisation rates for this review period were consistently above the record low levels seen in 2001/2002.

Figure 22. Mumps notifications and hospitalisations, Australia, 1993 to 2005,* by month of diagnosis or admission†

Figure 22. Mumps  notifications and hospitalisations, Australia, 1993 to 2005, by month  of diagnosis or admissio

* 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.

† Note that the number of jurisdictions notifying mumps increased over the review period until July 1996 when mumps became notifiable in all states and territories. From July 1999 until June 2001, mumps was not notifiable in Queensland. Only the Australian Capital Territory, New South Wales and Victoria notified for the entire review period.

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Severe morbidity and mortality

There were 549 hospital bed days (average 183 per year) recorded for patients with an ICD-10-AM code for mumps (Table 11). Of the 138 hospitalisations (average annual rate 0.23 per 100,000), 114 (83%) had mumps recorded as the principal diagnosis. Complications arising from mumps infection were recorded for 19 hospitalisations (14%). As in the past, the most commonly reported complication was orchitis. There were 10 (7%) hospitalised cases coded with orchitis; seven of these were between 15 and 59 years of age (Table 12). There were no hospitalisations coded as neurological (encephalitis or meningitis) or with multiple complications. The median length of stay (LOS) in hospital was two days, but adults aged 25 years and older had a longer median LOS compared with younger age groups (Table 11). The 15–24 year old age group had the highest hospitalisation rate and accounted for 20% of the hospitalisations. Adults over 15 years of age accounted for 75% of hospitalisations. Mumps was recorded as the underlying cause of death in one adult (aged 100 years) in 2004.

Table 11. Mumps 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
24
0.63
11
(9)
0.29
(0.24)
1.0 (1.0)
0
0.00
5–14
24
0.29
23
(20)
0.28
(0.25)
1.0 (1.0)
0
0.00
15–24
81
0.97
27
(24)
0.33
(0.29)
1.0 (1.0)
0
0.00
25–59
260
0.88
53
(50)
0.18
(0.17)
2.0 (2.0)
0
0.00
60+
30
0.28
24
(11)
0.23
(0.11)
6.0 (3.0)
1
0.01
All ages
419
0.69
138
(114)
0.23
(0.19)
2.0 (2.0)
1
0.003

* 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).

Table 12. Indicators of severe morbidity and mortality* for hospitalised cases of mumps, Australia, 2002 to 2005,* by age group

Age group
(years)
Mumps meningitis or encephalitis Mumps orchitis Mumps pancreatitis Mumps with other complications
n %
total
n %
total
n %
total
n %
total
0–4
0
0.00
0
0.00
0
0.00
1
9.09
5–14
0
0.00
0
0.00
1
4.35
1
4.35
15–24
0
0.00
3
11.1
0
0.00
1
3.70
25–59
0
0.00
4
7.55
1
1.89
1
1.89
60+
0
0.00
3
12.5
0
0.00
3
12.5
All ages
0
0.00
10
7.25
2
1.45
7
5.07

* 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

Since 2002, low notification rates have continued in the 0–14 year age group but there has been a notable increase in older age groups (Figure 23). In particular, during 2005 there was a high rate of notifications in the 25–29 year age group (5.1 per 100,000) as well as elevated rates in the 20–24 and 30–34 year old age groups. An upward trend in hospitalisations is not apparent (Figure 24), with the highest rates of admissions in those aged 5–9 years (0.45 per 100,000) and 70–74 years (0.47 per 100,000) over the three year period between July 2002 and June 2005.

The male:female ratio was 1.3:1 for notifications and 1.0:1 for hospitalisations over the three year review period. There was some variation by year in these ratios but the notifications and hospitalisations were broadly consistent with a similar level of mumps infection in males and females.

Figure 23. Mumps notification rates, Australia, 1999 to 2005,* by age group and year of diagnosis

Figure 23. Mumps  notification rates, Australia,  1999 to 2005, by age group and year of diagnosis

* Notifications where the month of diagnosis was between January 1999 and December 2005.

Figure 24. Mumps hospitalisation rates, Australia, 1999 to 2005,* by age group and year of separation

Figure 24. Mumps  hospitalisation rates, Australia,  1999 to 2005, by age group and year of separation

* Hospitalisations where the month of separation was between 1 July 1998 and 30 June 2005.

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Geographical distribution

The rise in notifications across the three year period was primarily due to an increase in Queensland (0.26 per 100,000 in 2003 rising to 1.79 per 100,000 in 2005) and New South Wales (0.52 per 100,000 in 2003 rising to 1.62 per 100,000 in 2005), although there have been smaller increases in Victoria and Western Australia (Appendix 2).

No obvious trends were apparent in hospitalisations due to small numbers in each jurisdiction (Appendix 3).

Vaccination status

Vaccination status was recorded for all 112 notifications of individuals born after 31/12/1980 in the 2003–2005 period but with 35 of these recorded as “unknown”. Of the 77 with vaccination status recorded, 24 were fully or partially vaccinated and 53 were unvaccinated. In the 7–15 year age range, 33% (6 of 18) of notifications were recorded as fully (5) or partially (1) vaccinated. Validation of vaccination status was recorded infrequently (8 of 77).

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Comment

After declining to record lows in 2002, notifications of mumps increased considerably during the period 2003–2005. This rise was primarily due to increased notification rates in the 20–34 year age group, with rates remaining low in the 0–4 year age group. The highest notification rate was experienced in the 25–29 year age group during 2005, with 5.1 per 100,000. Individuals in this age group were not eligible for routine mumps vaccination as infants, although they were targeted as part of the young adult MMR vaccination campaign in 2001. However, results from the second national serosurvey conducted by NCIRS suggest that this campaign had little impact on population immunity for measles, a conclusion that is also expected to apply to mumps.145

The rise in notifications was not reflected in the hospitalisation rates over the review period. This difference might be explained by the increase in notifications being primarily in the 20–34 year age group, for whom mumps hospitalisation may be relatively uncommon. The hospitalisation rate in this age group increased from the record low of 2001/2002, and was similar to the rates experienced in the late 1990s. The male:female ratios for hospitalisations and notifications were similar but there was some geographic variation in notifications by state, with Queensland and New South Wales experiencing the largest numbers of cases. An increasing trend in hospitalisations was not seen in these states.

Despite the increase in mumps notifications, rates in Australia were low in comparison to the rates experienced in the United Kingdom during the epidemic of mumps in 2004/2005. During 2005, there were 56,390 preliminarily confirmed cases of mumps reported in the UK,146 primarily affecting the 18–24 year age group in which the rate was above five per 1,000.147 Geographic movements of college students and waning of vaccine-derived immunity presumably contributed to the scale of this outbreak. The cohort most affected, although included in the UK national campaign of 1994, received measles-rubella (MR) not measles-mumps-rubella (MMR) vaccine, would have been ineligible for routine infant MMR vaccination and had limited exposure to circulating mumps virus.

In the USA, there were also significant numbers of mumps cases reported in 11 states following an outbreak in Iowa, with 2,597 cases reported between January and May 2006.148 Again, these cases were primarily in the 18–24 year age group. In Australia, notification rates have remained low. Nonetheless, in 2005, Australia exceeded the WHO incidence threshold for disease elimination of one case per 100,000. The higher notification rates in the 20–34 year age group suggest that some endemic transmission may be occurring in this age group. The rises in adult notifications of mumps over this reporting period and the recent experience in the USA and UK suggest that surveillance for mumps, with enhancement of immunisation efforts if necessary, is of continued importance in the Australian context.

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