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

Meningococcal disease

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

Meningococcal disease is defined as isolation of Neisseria meningitidis from cerebrospinal fluid (CSF), blood and other normally sterile sites as well as skin lesions. Clinical manifestations include meningitis, meningococcaemia without meningitis (which varies in presentation from fulminant to chronic), meningitis and meningococcaemia combined and septic arthritis. In culture-negative cases with a compatible clinical picture (such as fever, haemorrhagic rash and shock), a diagnosis of meningococcal disease can be supported by a range of other laboratory evidence. This includes the identification of Gram-negative intracellular diplococci or meningococcal antigen in blood or CSF, the identification of nucleic acid from Neisseria meningitidis in body fluids or demonstration of a serological response to Neisseria meningitidis.

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. Probable cases require specified clinical evidence only (as below) and are also notifiable.

  1. Laboratory definitive evidence
    • Isolation of Neisseria meningitidis from a normally sterile site.
  2. Laboratory suggestive evidence
    • Detection of meningococcus from a normally sterile site by nucleic acid testing; or
    • Detection of gram-negative diplococci in Gram stain of specimen from a normally sterile site or from a suspicious skin lesion; or
    • High titre IgM or significant rise in IgM or IgG titres to outer membrane protein antigens of N. meningitidis; or
    • Positive polysaccharide antigen test in cerebrospinal fluid with other laboratory parameters consistent with meningitis.

c. Clinical evidence (for confirmed cases with laboratory suggestive evidence)

    • Disease which in the opinion of the treating clinician is compatible with invasive meningococcal disease.

d. Clinical evidence for notification of probable cases

    • The absence of evidence for other causes of clinical symptoms and either
    • Clinically compatible disease including haemorrhagic rash; or
    • Clinically compatible disease AND close contact with a confirmed case within the previous 60 days.

Hospitalisations

The ICD-10-AM code used to identify hospitalisations was A39 (meningococcal infection). This includes meningococcal meningitis (A39.0), Waterhouse-Friderichsen syndrome (A39.1), acute meningococcaemia (A39.2), chronic meningococcaemia (A39.3), meningococcaemia unspecified (A39.4), meningococcal heart disease (A39.5), other meningococcal infections (A39.8), and meningococcal infection unspecified (A39.9). As all cases with one of these codes, not just principal diagnoses, were included, cases were identified in a hierarchical fashion to avoid double counting. First, those with code A39.0 (meningitis), then those without A39.0 but with A39.1 or A39.2 or A39.3 or A39.4 (septicaemia without meningitis), then those with none of these codes but with codes in any other subsection of A39 were selected. However, as re-admissions and inter-hospital transfers are separate records, duplication may occur for a condition such as meningococcal disease where complications are frequent.

Deaths

The ICD-10 code used to identify deaths was A39 (meningococcal infection).

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Secular trends

There were 1,355 notifications of meningococcal disease in the three years January 2003 to December 2005, an average annual notification rate of 2.2 per 100,000 population (Table 10). A median of 35.5 cases was notified each month, with a range of 17 to 83 cases. Between July 2002 and June 2005, there were 2,135 hospital admissions recorded as ICD code A39 (average annual rate 3.6 per 100,000), and a median of 50.5 cases (range 25–139) per month. Coinciding with the introduction of the national meningococcal C immunisation program in January 2003,136 both the notification and hospitalisation rates for meningococcal disease decreased each year, down from a peak in 2002 (Figure 15). The notification rate decreased by 39% from 2.8 cases per 100,000 in 2003 to 1.9 cases per 100,000 in 2005, while the hospitalisation rate decreased by 47% from 4.5 per 100,000 in 2002/2003 to 2.4 per 100,000 in 2004/2005.

A clear seasonal pattern was apparent, with the highest number of notifications and hospitalisations occurring between June and September each year (Figure 15).

Figure 15. Meningococcal notifications and hospitalisations, Australia, 1993 to 2005,* by month of diagnosis or admission

Figure 15. Meningococcal  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 separation was between 1 July 1993 and 30 June 2005.

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Severe morbidity and mortality

A total of 16,817 hospital bed days (average 5,606 days per year) were recorded for patients with an ICD-10-AM code of A39, of which 44% were coded as meningococcal meningitis (A39.0) and 46% were coded as septicaemia (A39.1–A39.4, not A39.0). The proportion where a meningococcal disease code was the principal diagnosis varied from 96% of cases among 0–14 year olds to 80% of cases for those aged 15–59 years and 67% for those aged 60 years and over. The average length of stay was six days and increased with age (Table 10).

From death certificate data, in 2003 and 2004 there were 46 deaths (0.12 per 100,000 population) with meningococcal disease recorded as the underlying cause of death (Table 10). Sixty-nine deaths were recorded for the 1,355 cases of meningococcal disease notified to NNDSS for the three years 2003–2005 (case fatality rate of 5%). Of the total 2,135 hospitalisations over three years (Table 10), 72 (3.4%) were recorded as dying before hospital discharge. The proportion of meningococcal infection hospitalisations that died before discharge increased steadily with age from approximately 2% for those aged 0–24 years to 5% for 25–59 year olds and 10% for those aged over 60 years.

Table 10. Meningococcal 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
427
11.3
657
(631)
17.3
(16.6)
5.0 (5.0)
12
0.48
5–14
174
2.1
307
(296)
3.8
(3.6)
4.0 (4.0)
1
0.02
15–24
365
4.4
559
(509)
6.8
(6.2)
6.0 (6.0)
12
0.22
25–59
289
1.0
468
(376)
1.6
(1.3)
7.0 (7.0)
10
0.05
60+
100
0.9
144
(96)
1.4
(0.9)
10.0 (9.0)
11
0.16
All ages
1,355
2.2
2,135
(1,908)
3.6
(3.2)
6.0 (6.0)
46
0.12

* 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 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 highest meningococcal disease notification, hospitalisation and death rates occurred among children less than five years of age (Table 10), with the highest in this age group among those under one year of age (24.5 notifications, 35.2 hospitalisations and 2.0 deaths per 100,000 population). There was a second peak in notification (Figure 16), hospitalisation (Figure 17) and death rates among 15–19 year olds (5.3, 8.6 and 0.26 per 100,000, respectively), with rates in 20–24 year olds remaining elevated, declining to lower levels in those 25 years of age and over (Table 10, Figures 16 and 17).

Overall, there was a predominance of male cases (male:female ratio 1.2:1). This was consistent across all groups aged less than 30 years. Among cases 30 years and older, rates were higher in females in several age groups, particularly those aged 75 years and over (1:1.8)

Figure 16. Meningococcal disease notification and death rates, Australia, 2003 to 2005,* by age group

Figure 16. Meningococcal  disease notification and death rates, Australia, 2003 to 2005, by age  group

* Notifications where the month of diagnosis was between January 2003 and December 2005; deaths where the death was recorded in 2003 or 2004.

Figure 17. Meningococcal disease hospitalisation rates, Australia, July 2002 to June 2005,* by age group

Figure 17. Meningococcal  disease hospitalisation rates, Australia,  July 2002 to June 2005, by age group

* Hospitalisations where the month of separation was between 1 July 2002 and 30 June 2005.

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Geographical distribution

The pattern of notification and hospitalisation rates for meningococcal disease varied across the country. The highest notification and hospitalisation rates were in the Northern Territory followed by Tasmania (Appendix 2 and Appendix 3). There was a decrease in notification rates between 2003 and 2005 in all states and territories. The largest decreases occurred in Tasmania (4.2 to 2.1 cases per 100,000 in 2003 and 2005, respectively) and Queensland (2.8 to 1.6 cases per 100,000 in 2003 and 2005, respectively).

Hospitalisation rates also decreased between 2002/03 and 2004/05 for all jurisdictions except the Northern Territory and the Australian Capital Territory. This decease was greatest in Victoria (5.0 to 1.7 per 100,000 in 2002/03 and 2004/05, respectively) and Queensland (5.3 to 2.2 cases per 100,000 in 2002/03 and 2004/05, respectively) (Appendix 3).

In 2003–2005, among the jurisdictions that reported whether cases were part of an outbreak of meningococcal disease, there were 23 notified cases linked to 11 outbreaks. Outbreaks were recorded in South Australia, Victoria, Queensland and Western Australia.

Meningococcal serogrouping and vaccination

Meningococcal serogroup information was recorded for 84% of the 1,355 notified cases in 2003–2005, a higher proportion than in previous years (Figure 18). In 2003–2005, there were 795 notified cases (1.3 per 100,000 population) of serogroup B meningococcal disease and 280 cases (0.5 per 100,000 population) of serogroup C disease. Serogroup B disease notifications remained stable for all age groups while the number of notifications of serogroup C disease decreased substantially – by 80% from 225 in 2002 to 46 in 2005 (1.15 to 0.23 per 100,000 population) (Figure 18). As a proportion of total notifications for meningococcal disease, serogroup C decreased from 33% in 2002 to 12% in 2005.

Figure 18. Meningococcal disease notifications, Australia, 1991 to 2005, by serogroup

Figure  18. Meningococcal disease  notifications, Australia,  1991 to 2005, by serogroup

Much of the decrease in serogroup C disease notifications occurred among the age groups targeted for the national meningococcal C vaccination program during 2003–2005 (Figure 19).136 A decrease in serogroup C notifications was also evident among age groups not included in the vaccination program, including adults aged 25–39 years and those aged 65 years and over (Figure 20). Serogroup C notifications for infants aged less than one year remained low, with an average of four per year (1.7 cases per 100,000 population) compared with an average of 48 serogroup B notifications per year (19.1 cases per 100,000 population).

Figure 19. Meningococcal serogroup C disease notifications, Australia, 1999 to 2005, by age group eligible for the meningococcal C vaccination program*

Figure  19. Meningococcal serogroup C  disease notifications, Australia, 1999 to 2005, by age group eligible for the  meningococcal C vaccination program

* Shows the age groups eligible for the meningococcal C vaccination program from 1 January 2003 (those aged 1–19 years).

Figure 20. Meningococcal serogroup C disease notifications, Australia, 1999 to 2005, by age group*

Figure  20. Meningococcal serogroup C  disease notifications, Australia,  1999 to 2005, by age group

* Shows the age groups not included in the meningococcal C vaccination program.

Note: different scales for Figures 19 and 20.

During 2003–2005, there was considerable heterogeneity between jurisdictions in the relative notification rates of serogroup B and serogroup C meningococcal disease (Figure 21). Following the introduction of the national meningococcal C vaccination program in January 2003, there was an impressive reduction in notification rates across most states and territories with the largest reductions in Tasmania and Victoria (Figure 21).

Figure 21. Meningococcal disease notification rates, Australia, by jurisdiction and serogroup

Figure  21. Meningococcal disease  notification rates, Australia,  by jurisdiction and serogroup

Meningococcal C vaccination status was recorded for 165 (59%) of the 280 notified cases of serogroup C disease and 84 (70%) of the 120 cases aged 19 years and under. There were two reports of vaccine failure in children aged 1–4 years; both

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Comment

The incidence of meningococcal disease in Australia increased continuously between 1991 and 2002.3 Following the introduction of the routine and catch-up meningococcal C vaccination programs in January 2003 for those born after 1983 (aged 19 years in 2003),136 there has been a marked decrease in meningococcal disease notifications, hospitalisations and deaths. The reduction in notifications occurred for both serogroup C disease and those where serogroup information was not available, while notifications for serogroup B and other serogroups, mainly W135 and Y, remained relatively stable.

The decrease in serogroup C disease notifications occurred among all the age groups included in the mass vaccination program, particularly those aged 15–19 years at the time of diagnosis. There was also a smaller decrease in serogroup C notifications among two age groups not targeted by the national immunisation program, the 25–39 years and 65 years and over age groups. The 20–24 year age group (age at diagnosis) included some who would have received meningococcal C vaccine as part of the program, plus some who may have been protected by herd immunity, primarily as a consequence of the mass immunisation program and possibly to a lesser extent from natural exposure to pharyngeal infection/colonisation with serogroup C.137 Federal funding for the serogroup C vaccination program has been extended until June 2007 to allow continued catch-up in ‘hard to reach’ groups such as those now aged in their early 20s.138

Data reported by the National Neisseria Network,12 and related disease notification data reported elsewhere,139 indicate that the majority (77% in 2005)139 of meningococcal disease is due to serogroup B with the highest rate among children less than one year of age. Like other countries that have implemented national meningococcal C immunisation programs, there is no evidence to date of an increase in the incidence of serogroup B disease in Australia due to serogroup replacement in the vaccinated population.12,140,141

Meningococcal disease hospitalisations have been consistently higher than notifications since 1997 (Figure 15). A number of factors may contribute to this discrepancy including inter-hospital transfers (approximately 10% of separations for meningococcal disease), coding of some meningitis admissions as meningococcal disease and incomplete notification of hospitalised cases to public health authorities.

The high burden of meningococcal disease in infants, particularly non-vaccine preventable serogroup B disease, emphasises the importance of early recognition and appropriate clinical management of disease and the need for a vaccine to reduce the significant morbidity and mortality. Several candidate serogroup B vaccines are under investigation in international Phase II clinical trials.142 However, availability of a universal serogroup B vaccine appropriate for use in Australia is still some way off. In New Zealand, a vaccine, based on a particular strain of meningococcus B that was responsible for a major upsurge in disease over an extended period, has proved successful. High rates of vaccine uptake were achieved (more than three million doses distributed) and the rate of disease has been substantially reduced in line with a vaccine effectiveness of about 80% against the epidemic strain.143,144

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