Vaccine Preventable Diseases in Australia, 2005 to 2007

3.10 Pneumococcal disease

Page last updated: 24 December 2010

Pneumococcal disease is caused by the bacterium Streptococcus pneumoniae (pneumococcus). Pneumococci can be isolated from the upper respiratory tract in children and, less frequently, adults, and can spread directly from the nasopharynx to the respiratory tract which may cause otitis media, sinusitis or pneumonia. Pneumococci are also able to enter the bloodstream to cause invasive disease which may manifest as meningitis, pneumonia, septicaemia without focal infection or, less commonly, infection of other sites such as the pleura, the peritoneum or the joints. Invasive pneumococcal disease (IPD) is diagnosed by detection of S. pneumoniae in the blood, cerebrospinal fluid or other sterile sites. In the absence of a sterile site isolate, a presumptive diagnosis of pneumococcal pneumonia may be based on a sputum isolate of S. pneumoniae and/or clinical or radiological features, such as characteristic chest x-ray appearance or prompt response to antibiotic therapy.1

Historically, worldwide and in Australia, IPD has predominantly affected the very young, the very old, indigenous populations, and people with certain chronic diseases or high-risk conditions.2,3 In Australia, vaccination with the 23-valent pneumococcal polysaccharide vaccine (23vPPV) has been funded nationally since 1999 for Aboriginal and Torres Strait Islander adults aged ≥50 years, and Aboriginal and Torres Strait Islander people aged 15–49 years with high-risk conditions.4 A nationally funded vaccination program using the 7-valent pneumococcal conjugate vaccine (7vPCV) commenced in 2001 for all Aboriginal and Torres Strait Islander infants and young children, and non-Indigenous Australian children with certain high-risk conditions.5 Since 2005, 7vPCV has been publicly funded for all Australian infants (with a catch-up program for children aged <2 years), and 23vPPV has been publicly funded for all adults aged ≥65 years.6

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Case definitions

Notifications7

Only confirmed IPD cases are notifiable. Notification has occurred since 1995 in the Northern Territory, since 1997 in Queensland and since January 2001 Australia wide. Confirmation of IPD is through:

  1. Isolation of Streptococcus pneumoniae from a normally sterile site by culture; or
  2. Detection of Streptococcus pneumoniae from a normally sterile site by nucleic acid testing.

Hospitalisations

The ICD-10-AM codes used to identify hospitalisations were: G00.1 (pneumococcal meningitis); A40.3 (pneumococcal septicaemia) (together, these two codes were considered to be a proxy for IPD); and J13 (pneumococcal pneumonia). To avoid double counting, cases were identified in a hierarchical fashion. First, all those with code G00.1 were classified as meningitis, then those without G00.1 but with A40.3 were classified as ‘septicaemia without meningitis’, and lastly, those with neither of these codes but with code J13 were counted as ‘pneumococcal pneumonia without meningitis or septicaemia’. A combined category of ‘Pneumococcal disease’ included all hospitalisations with one or more of these pneumococcal codes.

Deaths

ICD-10 codes G00.1, A40.3 and J13 were used to select deaths attributed to pneumococcal disease.

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Secular trends

Notification rates and hospitalisation rates for pneumococcal disease decreased in 2006 and 2007 compared with previous years in all age groups. In 2006–2007, there were a total of 2,937 notifications of IPD, 1,464 in 2006 and 1,473 in 2007, with an average annual notification rate of 7.0 per 100,000 for the 2 years (Table 3.10.1). Compared with the average national notification rate in 2002–2004 (11.8 per 100,000 population), there was a 40% decrease in the IPD notification rate in 2006–2007 (Table 3.10.2).

Between July 2005 and June 2007, there were 4,515 hospital separations coded as pneumococcal meningitis, septicaemia or pneumonia, with 2,326 in the 12 months July 2005 to June 2006, and 2,189 in the 12 months July 2006 to June 2007. The average annual rate of hospitalisation was 11.0 per 100,000 (Table 3.10.1). This is a 35% decrease compared with the average annual hospitalisation rate in July 2002–June 2004 (16.8 per 100,000) (Table 3.10.3).

An obvious seasonality with winter peaks was observed for both IPD notifications and hospitalisations for pneumococcal disease during their respective 2-year reporting periods (Figure 3.10.1). This seasonality was similar to that observed in previous years prior to the introduction of the universal infant pneumococcal conjugate vaccine program in 2005. However, both the peak and trough incidences in the post-vaccine introduction period were lower compared with the previous period. The median number of IPD notifications and pneumococcal disease hospitalisations in the winter months (May to October) of 2006, which was within the reporting period of both the notification and hospitalisation data, was 156.5 and 238.5 per month, respectively. This compared with 286.5 per month for notifications and 341 per month for hospitalisations in the winter of 2004. The median number of notifications per month for IPD in the summer months (November to April) of 2005/2006 and 2006/2007 was 87, and that of hospitalisations with a pneumococcal disease code was 136 per month. These compared with 136.5 notifications per month and 191.5 hospitalisations per month for the summer of 2003/2004.

Figure 3.10.1: Pneumococcal disease notifications and hospitalisations, Australia, 1998 to 2007,* by month of diagnosis or admission

Figure 3.10.1:  Pneumococcal disease notifications and hospitalisations, Australia, 1998 to 2007, by month of diagnosis or admission

* Notifications where the date of diagnosis was between January 2001 and December 2007; hospitalisations where the date of admission was between July 1998 and June 2007. Hospitalisations include pneumonia, meningitis and septicaemia.

Pneumococcal pneumonia was recorded as the principal diagnosis in 67.6% (2,090/3,092) of hospitalisations where ‘pneumococcal pneumonia without pneumococcal meningitis or septicaemia’ was one of the diagnoses for the hospitalisation. The median number of hospitalisations per month for ‘pneumococcal pneumonia without meningitis or septicaemia’ was 114 (range 54–222), while for pneumococcal meningitis or septicaemia it was 51 (range 17–109). For the months of May–October in 2005 and 2006, the median number of hospitalisations per month for ‘pneumococcal pneumonia without meningitis or septicaemia’ was 168.5, while that for pneumococcal meningitis or septicaemia was 87.5.

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Severe morbidity and mortality

Between July 2005 and June 2007, a total of 49,945 hospital bed days were recorded for hospital separations with ICD-10-AM codes corresponding to pneumococcal meningitis, septicaemia or pneumonia, with an average of 24,973 hospital bed days per year. The average number of bed days was shorter in this reporting period than the period from July 2002 to June 2005.8 The overall median length of stay for hospitalisations coded with any of these codes increased with age (Table 3.10.1). For pneumococcal meningitis, the overall median length of hospital stay was 11 days, compared with 7 days for ‘septicaemia without meningitis’ and 6 days for ‘pneumonia without meningitis or septicaemia’.

Of the 48 reported pneumococcal deaths in 2005–2006 in the AIHW National Mortality Database, the underlying cause of death was recorded as pneumococcal meningitis in 10 (21%), pneumococcal septicaemia in 11 (23%), and pneumococcal pneumonia in 27 (56%) cases. The mortality rate was greatest in adults ≥60 years of age (0.36 per 100,000 population) for all sites of infection, followed by children aged <5 years (0.23 per 100,000 population) (Table 3.10.1). Of all 2,937 IPD notifications reported to NNDSS in 2006 and 2007, death was reported in 249 (8.5%) cases, but whether death eventuated was unknown for 1,093 (37%) cases. For the reporting year 2006, for which both notification data and death registry data in the AIHW National Mortality Database are available, there were 130 deaths among the notified cases recorded in the NNDSS, and 25 deaths recorded in the registry. Two of the 24 recorded deaths that actually occurred in 2006 were in children aged <2 years and 12 were in people aged ≥65 years. Of the 130 IPD deaths reported in NNDSS in 2006, 4 were in children aged <2 years and 85 were in people aged ≥65 years.

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Table 3.10.1: Pneumococcal disease notifications, hospitalisations and deaths, Australia, 2005 to 2007,* by age group

Age group
(years)
Notifications
(IPD) 2 years
(2006–2007)
Hospitalisations
(pneumococcal disease) 2 years
(July 2005–June 2007)
LOS per admission
(days)
Deaths
(pneumococcal disease)
2 years
(2005–2006)
n Rate n§ (M/S)|| Rate‡,§ (M/S)‡,|| Median§ (M/S)|| n§ (M/S)|| Rate‡,§ (M/S)‡,||
0–4
443
16.8
343
(184)
13.2
(7.1)
4.0
(5.0)
6
(5)
0.23
(0.19)
5–14
142
2.6
135
(73)
2.5
(1.3)
4.0
(4.0)
1
(1)
0.02
(0.02)
15–24
120
2.1
158
(41)
2.8
(0.7)
4.0
(5.0)
2
(1)
0.04
(0.02)
25–59
1,042
5.1
1,683
(510)
8.4
(2.5)
6.0
(7.5)
13
(8)
0.06
(0.04)
60+
1,188
15.9
2,196
(615)
30.3
(8.5)
8.0
(9.0)
26
(6)
0.36
(0.08)
All ages
2,937
7.0
4,515
(1,423)
11.0
(3.5)
6.0
(8.0)
48
(21)
0.12
(0.05)

* Notifications where the date of diagnosis was between January 2006 and December 2007; hospitalisations where the date of separation was between July 2005 and June 2007; deaths where the death was recorded between January 2005 and December 2006.

† LOS = length of stay in hospital.

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

§ Pneumococcal meningitis, septicaemia or pneumonia.

|| M/S = pneumococcal meningitis or septicaemia (proxy for invasive pneumococcal disease).

¶ Includes 2 cases with unknown age.

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Age and sex distribution

In both 2006 and 2007, the age distribution of notified IPD cases was in line with previous data, with highest notification rates in the elderly and young children (Table 3.10.1). Among adults aged ≥65 years, as age increased, so did the notification rate. The highest rates were in those aged ≥85 years (33.9 per 100,000 population) compared with those aged 80–84 years (23.1 per 100,000 population) and 75–79 years (19.1 per 100,000 population). Rates were highest in children aged 12–23 months (28.7 per 100,000 population) compared with all other 12-month age groups under 5 years.

Figure 3.10.2 clearly shows the decrease in reported IPD notification rates among children <2 years of age since introduction of universal 7-valent pneumococcal conjugate vaccination for young children in 2005. Average annual notification rates decreased by 74% between 2002–2004 and 2006–2007 in the age groups targeted for vaccination (children aged <2 years) (Table 3.10.2). There was a decrease of 64% in the notification rate, to 11.4 per 100,000 population, in children aged 2–4 years, most of whom would also have been eligible for vaccination. In the same period, there were also decreases in notification rates in age groups not targeted by the childhood vaccination program, by 28% in those aged 15–49 years, 23% in those aged 50–64 years, and by 29%, to 18.0 per 100,000 population, in those aged ≥65 years.

Figure 3.10.2: Pneumococcal disease notification rates, Australia, 2002 to 2007,* by age group and year of diagnosis

Figure 3.10.2:  Pneumococcal disease notification rates, Australia, 2002 to 2007, by age group and year of diagnosis

* Notifications where the date of diagnosis was between January 2002 and December 2007.

Table 3.10.2: Average annual notification rates and percentage change in notification rates of invasive pneumococcal disease, Australia, 2006–2007 compared with 2002–2004, by age group

Age group
(years)
Average rate
2002–2004*
Average rate
2006–2007
Change (%)
<2
95.4
24.6
–74
2–4
31.9
11.4
–64
5–14
3.8
2.6
–32
15–49
5.5
3.9
–28
50–64
9.8
7.5
–23
65+
25.5
18.0
–29
All ages
11.8
7.0
–40

* Average age-specific rate per 100,000 population. Notifications where the date of diagnosis was between January 2002 and December 2004.

† Average age-specific rate per 100,000 population. Notifications where the date of diagnosis was between January 2006 and December 2007.

‡ Percentage change in the average notification rate of 2006–2007 compared with the average notification rate of 2002–2004.

Between July 2005 and June 2007, hospitalisation rates for pneumococcal disease were greater in adults aged ≥60 years (30.3 per 100,000 population) than in children aged <5 years (13.2 per 100,000 population) (Table 3.10.1). For all ages, the rate of hospitalisation for ‘pneumococcal pneumonia without meningitis or septicaemia’ was greater than for pneumococcal meningitis or pneumococcal septicaemia without meningitis (Figure 3.10.3). For pneumonia (without meningitis or septicaemia) and septicaemia (without meningitis), there was a small peak among children aged <5 years, and a larger peak in the elderly age groups. The hospitalisation rate for ‘pneumonia without meningitis or septicaemia’ peaked at 39.1 hospitalisations per 100,000 population in the ≥85 years age group, and the peak for ‘septicaemia without meningitis’ was 17.8 per 100,000 population in the same age group. In contrast, the age distribution of hospitalisation rates for pneumococcal meningitis showed a peak only among young children, with the highest rate in children aged <5 years (2.0 per 100,000 population) (Figure 3.10.3).

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Figure 3.10.3: Pneumococcal meningitis, septicaemia and pneumonia hospitalisation rates, Australia, 2005/2006 to 2006/2007,* by age group

Figure 3.10.3:  Pneumococcal meningitis, septicaemia and pneumonia hospitalisation rates, Australia, 2005/2006 to 2006/2007, by age group

* Hospitalisations where the date of separation was between July 2005 and June 2007.

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Average hospitalisation rates of pneumococcal disease in all age groups decreased in the period July 2005 to June 2007 compared with the period July 2002 to June 2004. There were decreases of 72% for those aged <2 years, 58% for those aged 2–4 years and 33% for those aged 50–64 years (Table 3.10.3). During the period July 2005 to June 2007, the ≥65 years age group had the highest hospitalisation rate (34.9 hospitalisations per 100,000). For hospitalisation rates of pneumococcal ‘pneumonia without meningitis or septicaemia’, the proportional change between July 2005–June 2007 and July 2002–June 2004, as well as the relative age group distribution, were similar to those of hospitalisations for pneumococcal disease (Table 3.10.3).

For the 2-year reporting periods, both IPD notification and pneumococcal disease hospitalisation rates were higher in males than in females for most age groups and overall (male:female ratio 1.3:1 for both notification and hospitalisation rates).

Table 3.10.3: Average annual hospitalisation rates and percentage change in hospitalisation rates for pneumococcal disease and for pneumococcal pneumonia without meningitis or septicaemia, Australia, 2005/2006–2006/2007 compared with 2002/2003–2003/2004, by age group

Age group
(years)
Average rate 2002/2003–2003/2004* Average rate 2005/2006–2006/2007 Change (%)
Pneumococcal disease§ Pneumococcal pneumonia|| Pneumococcal disease§ Pneumococcal pneumonia|| Pneumococcal disease§ Pneumococcal pneumonia||
<2
71.8
26.0
20.1
8.3
–72
–68
2–4
20.4
10.3
8.6
4.6
–58
–55
5–14
4.0
2.4
2.5
1.1
–38
–54
15–49
8.5
6.3
6.1
4.3
–27
–32
50–64
19.0
13.8
12.8
8.9
–33
–36
65+
49.1
35.7
34.9
25.4
–29
–29
All ages
16.8
11.4
11.0
7.5
–35
–34

* Average age-specific rate per 100,000 population. Hospitalisations where the date of separation was between July 2002 and June 2004.

† Average age-specific rate per 100,000 population. Hospitalisations where the date of separation was between July 2005 and June 2007.

‡ Percentage change in the average hospitalisation rate of 2005/2006–2006/2007 compared with the average hospitalisation rate of 2002/2003–2003/2004.

§ Pneumococcal meningitis, septicaemia and/or pneumonia

|| Pneumococcal pneumonia without meningitis or septicaemia.

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Geographical distribution

The average annual notification rate of IPD of 28.7 per 100,000 population in the Northern Territory in 2006–2007 was about 4 times that of the national rate (7.0 per 100,000) and the highest rate in any jurisdiction, as was the case in previous years. The average annual notification rates ranged from 5.4 to 8.0 in other jurisdictions in 2006–2007 (Appendix 6.2).

A similar distribution was seen in the hospitalisation rates. In 2005/2006–2006/2007, the average annual hospitalisation rate for pneumococcal disease (pneumococcal meningitis, septicaemia or pneumonia) of 42.4 per 100,000 in the Northern Territory was 3.9 times that of the national rate of 11.0 per 100,000 population. Hospitalisation rates in other jurisdictions ranged between 8.2 and 11.8 per 100,000 population. In the same period, the hospitalisation rate for pneumococcal pneumonia without meningitis or septicaemia in the Northern Territory (24.2 per 100,000) was 3.2 times that of the national average rate (7.5 per 100,000; range 5.9–8.0 per 100,000 for other jurisdictions). The average annual hospitalisation rate for pneumococcal meningitis or septicaemia (a proxy for IPD) in the Northern Territory (18.2 per 100,000) was about 5 times that of the national rate (3.5 per 100,000), while that of other jurisdictions ranged between 2.4 and 3.8 per 100,000 (Appendix 6.3).

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Pneumococcal typing

Data on the pneumococcal serotypes of notified IPD cases during 2006–2007 were available for 89% (2,601/2,937) of all notified cases, compared with 81% (5,722/7,050) of all notified cases during 2002–2004, the 3 years prior to introduction of the universal 7vPCV program. Of the 335 notifications in 2006–2007 with unknown or missing serotype information, the majority (222/335, 66%) were aged 5–64 years, the age groups where enhanced surveillance for IPD notifications was not implemented in some jurisdictions. The proportion of notified cases in 2006–2007 with unknown or missing serotype information in those aged <5 years, 5–64 years and ≥65 years were 7.9%, 14.7% and 11.5%, respectively.

Thirty-five per cent (918) of all serotyped cases during 2006–2007 were caused by serotypes contained in the 7vPCV, compared with 73% in 2002–2004. During 2006–2007, among children targeted by the program (i.e. aged <2 years), 20% (47/241) of serotyped cases were caused by serotypes in the 7vPCV compared with 85% (1,049/1,242) in 2002–2004.8

The notification rate of IPD caused by 7vPCV serotypes in 2006–2007 decreased overall by 68%, to 2.2 per 100,000, when compared with that in 2002–2004. The rate of IPD caused by 7vPCV serotypes decreased in age groups targeted by the vaccination program, as well as in groups not targeted by the program, but the decrease was greatest among children <5 years of age. Among children <2 years of age, there was a 94% decrease (from 69.7 per 100,000 population to 4.4 per 100,000 population) (Figure 3.10.4, Table 3.10.4).

For most age groups, in 2006–2007 compared with 2002–2004, there were increases in notification rates of IPD caused by serotypes that are contained in the 23vPPV but not in the 7vPCV (23v-non-7v serotypes), and serotypes not included in either vaccine (non-23vPPV serotypes) (Table 3.10.4). The percentage increases in average annual notification rates caused by serotypes not contained in the 7vPCV ranged between 24% and 89% among different age groups (Table 3.10.4). The greatest absolute increases in the average annual notification rates of IPD caused by non-7vPCV serotypes were seen in children aged <2 years, children aged 2–4 years, and adults aged ≥65 years (Figure 3.10.4). The increases in rates were 5.2, 3.5 and 3.3 cases per 100,000 population, respectively. Overall, the increase in non-23vPPV serotypes was less than that in 23v-non-7v serotypes (Table 3.10.4).

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Figure 3.10.4: Notification rates of IPD cases with serotypes contained in the 7-valent pneumococcal conjugate vaccine (7vPCV),* versus notification rates for other non-7-valent serotypes, Australia, 2006–2007 compared with 2002–2004, by age group

Figure 3.10.4:  Notification rates of IPD cases with serotypes contained in the 7-valent pneumococcal conjugate vaccine (7vPCV), versus notification rates for other non-7-valent serotypes, Australia, 2006-2007 compared with 2002-2004, by age group

* Serotypes contained in the 7-valent pneumococcal conjugate vaccine: 4, 6B, 9V, 14, 18C, 19F, 23F.

† All IPD cases with known serotypes and age caused by serotypes not contained in the 7-valent pneumococcal conjugate vaccine.

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Table 3.10.4: Percentage change in the average annual notification rates* of invasive pneumococcal disease cases, Australia, 2006–2007 compared with 2002–2004, by age group and serotype category

Age group
(years)
Serotype category
7v (%) 23v-non-7v (%) Non-23v§ (%) All non-7v combined|| Serotypes unknown/missing
<2
–94
+71
–10
+41
–83
2–4
–87
+131
+29
+89
–82
5–14
–54
+55
–46
+24
–40
15–49
–60
+65
+22
+53
–50
50–64
–51
+56
+93
+63
–68
65+
–53
+46
+57
+49
–69
All ages
–68
+62
+36
+55
–64

* Notifications to the National Notifiable Diseases Surveillance System, per 100,000 population.

† Serotypes contained in the 7-valent pneumococcal conjugate vaccine: 4, 6B, 9V, 14, 18C, 19F, 23F.

‡ Serotypes contained in the 23-valent pneumococcal polysaccharide vaccine but not in the 7-valent pneumococcal conjugate vaccine: 1, 2, 3, 5, 7F, 8, 9N, 10A, 11A, 12F, 15B, 17F, 19A, 20, 22F, 33F.

§ Serotypes not contained in either vaccine.

|| All other serotypes except the 7 serotypes contained in the 7-valent pneumococcal conjugate vaccine.

In children <5 years of age the predominant 23v-non-7v serotype in 2006–2007 was 19A (28.9% of IPD notifications, average annual rate 4.8 per 100,000 population), and the predominant non-23vPPV serotype was 6A (6.5%, average annual rate 1.1 per 100,000 population). The notification rate for serotype 19A in 2006–2007 was 2.3 times that in 2002–2004, but the notification rate for serotype 6A decreased by 37% in 2006–2007 compared with 2002–2004.

For adults aged ≥65 years, the rate of IPD caused by 7vPCV serotypes decreased by 53% in 2006–2007 compared with 2002–2004, while 23v-non-7v and non-23vPPV serotypes increased, by 46% and 57%, respectively (Table 3.10.4). In those aged ≥65 years there was a broader distribution of serotypes, with the predominant 23v-non-7v serotypes being serotype 3 (9.5% of IPD notifications), 19A (7.8%) and 22F (8.3%), while 6A was again the predominant non-23vPPV serotype (7.1%). Notification rates of these serotypes increased between 2002–2004 and 2006–2007 by 35%, 95%, 55% and 16%, respectively.

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Vaccination status

From 1 January 2005, children born from 1 January 2003 were eligible for a full course of the funded 7vPCV and catch-up programs. Of 336 eligible children aged >6 months at disease onset and reported to NNDSS in 2006–2007 as IPD cases, data on vaccination status were available for 281 (84%). Of those, 220 (78% of 281) were reported to be fully vaccinated, and this was validated by vaccination records for 215 (98% of 220). Of the 220 fully vaccinated cases, 22 (10%) had 7vPCV serotypes, 143 (65%) had 23vPPV serotypes and 37 (17%) had other non-23vPPV serotypes. The vaccination status was validated by written confirmation for all (22 of 22) 7vPCV serotype cases, 139 (97% of 143) 23vPPV serotype cases and 36 (97% of 37) of the other non-23vPPV serotype cases. A status of being partially vaccinated was reported for 34 (12% of 281) cases, and 27 (10% of 281) were reported to be unvaccinated.

Among notified IPD cases aged ≥65 years in 2006–2007, vaccination status was reported for 563 of 981 cases (57%). Twenty-six per cent (253/981) were reported as fully vaccinated, 6% (57/981) as partially vaccinated and 26% (253/981) as unvaccinated, while vaccination status information was not available for 418 (43%).

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Comment

The substantial impact of the universal 7vPCV program on Australian hospitalisation and notification rates of pneumococcal disease is highlighted in this report. Between 2002–2004 and 2006–2007, there were decreases in the overall average annual notification rate (from 11.8 to 7.0 per 100,000 population), notification rates in all age groups, and notification rates of IPD caused by 7vPCV serotypes. Hospitalisation data from 2005/2006–2006/2007, compared with previous years, showed decreased overall average annual rates (from 16.8 per 100,000 in 2002/2003–2003/2004 to 11.0 per 100,000), and decreased rates in all age groups, and for the various clinical manifestations of pneumococcal disease.

Reduction in the IPD notification rate is most pronounced in the target age group of the universal 7vPCV program, those <2 years of age, especially with respect to IPD caused by 7vPCV serotypes. As has been observed in other countries,9–11 the 7vPCV vaccination program has had a protective effect on unimmunised as well as immunised age groups in Australia, with decreases in notification and hospitalisation rates observed in age groups both targeted and not targeted by the 7vPCV program. This effect is due to herd immunity mediated by the universal 7vPCV program and subsequent reductions in carriage of pneumococci12,13 and in transmissions to the unvaccinated.10 In addition to herd immunity effects, it is possible that catch-up vaccination with 7vPCV in children aged <2 years when the 7vPCV program was initially implemented in 2005 would have contributed to decreased IPD rates in children aged 2–4 years in 2006–2007.

Concerns about replacement disease by serotypes not contained in the 7-valent vaccine have been expressed overseas14 and in Australia.15–17 In the USA, increases in non-7-valent serotypes have been documented post implementation of the national vaccination program.9,18 However, overall in the USA, the decreased disease rates attributable to 7vPCV outweigh the smaller increases in non-vaccine serotypes.10 An exception to this is one region of Alaska, where increases in serotype 19A have been greater than the decreases in 7vPCV serotypes, resulting in a net increase in total IPD rates in Alaskan Natives after implementation of their vaccination program.19 In the data presented here and also reported from Victoria,16 the increases in notifications of non-vaccine serotypes in Australia to date appear similar to the situation seen in the general US population. Continued monitoring of this situation is clearly important.

The 23vPPV has been shown to be effective against IPD in older adults who did not have high prevalence of risk factors,20–22 but its effectiveness may be poorer in populations with chronic disease or high-risk conditions,22 including Indigenous populations.23 The effectiveness of the 23vPPV against nasopharyngeal carriage and pneumococcal pneumonia has not been established.22 The decreases seen in hospitalisation and notification rates in those aged ≥65 years in 2006–2007, compared with 2002–2004, are largely due to decreases in IPD caused by serotypes contained in the 7vPCV, implying a herd immunity effect. The proportion of the decrease attributable to universal adult 23vPPV vaccination is not clear. In this age group, there were increased rates of IPD caused by both non-23vPPV serotypes and 23v-non-7v serotypes. The increase in rates of IPD caused by non-23vPPV serotypes may reflect the extent of ‘natural’ increase due to serotype replacement in the community after implementation of the 7vPCV program. The comparatively smaller increase in the rate of IPD caused by non-23vPPV serotypes in this age group suggests that, overall, there might be a modest protective effect achieved by the 23vPPV in those aged ≥65 years.

This report documents lower hospitalisation rates after the implementation of the universal 7vPCV program in Australia, shorter lengths of hospital stays, and fewer deaths recorded as due to pneumococcal meningitis, septicaemia or pneumonia. Overall, hospitalisation rates for pneumococcal disease (including pneumococcal pneumonia without meningitis or septicaemia) were higher than IPD notification rates. The hospitalisation codes used to identify pneumococcal disease were less specific than the case definition used for notification data (which only includes invasive disease), as they include pneumococcal pneumonia without bacteraemia, and microbiological detection of S. pneumoniae is not mandatory for assigning diagnosis in the hospitalisation data. As expected, hospitalisation rates for pneumococcal meningitis or septicaemia, used as a proxy indicator for IPD, were lower than IPD notification rates for all age groups. In addition to protection against IPD, 7vPCV may protect against other pneumococcal infections including non-bacteraemic pneumococcal pneumonia and otitis media.14,24,25 The observed decreases in the rate of pneumococcal pneumonia hospitalisation are a potential indicator of the vaccine’s effectiveness against non-invasive pneumococcal infection.

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The total number of pneumococcal disease deaths reported to the AIHW National Mortality Database halved in 2005–2006 compared with the previous 2 years. The age distribution of the deaths was unchanged, with the majority occurring in the elderly. Even though these deaths reported to the registry included the broader category of all pneumococcal pneumonia, in 2006 there were 5.4 times as many pneumococcal deaths reported through NNDSS as through registry reports (which are based only on the underlying cause of death, not including other contributing causes of death). This suggests that pneumococcal pneumonia as the underlying cause of death is under-reported in registry data. The crude case-fatality rate from the notification data in NNDSS (8.5%) falls in the range of case-fatality rates reported from elsewhere in the vaccine era; between 5% and 27%.11,26 However, the validity of outcome data in NNDSS should be interpreted with caution because of poor completeness.

Higher rates of IPD have been reported in Aboriginal and Torres Strait Islander young children and adults than in non-Indigenous Australians in several regions of Australia.27–29 The completeness of identification of Indigenous status in the national notification and hospitalisation datasets is highly variable across different jurisdictions, in particular among age groups that are not subjected to enhanced IPD surveillance in some jurisdictions. This limits the usefulness of epidemiological analysis of national data on pneumococcal disease by Indigenous status. A report on notification and hospitalisation data among Aboriginal and Torres Strait Islander people by various age groups, from selected jurisdictions with acceptable completeness of Indigenous status identification in records over the period 2003–2006, has been published.4 While a detailed analysis of IPD in Indigenous people is not the subject of this chapter, previous analyses have shown substantial reductions in 7vPCV-type IPD, but continuing high rates of non-vaccine type IPD, similar to levels seen prior to widespread vaccination.4,15 Serotypes causing infection in indigenous populations worldwide have been more diverse than those causing infection in non-indigenous populations, meaning that there is less protection provided by currently available conjugate vaccines for indigenous people.3 Conjugate vaccines with extended serotype valencies or novel protein-based pneumococcal vaccines (which are under preliminary development) may potentially contribute to achieving further reductions in disease, particularly in Indigenous Australians.

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References

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3. National Health and Medical Research Council. The Australian Immunisation Handbook. 9th edn. Canberra: Australian Government Department of Health and Ageing, 2008.

4. Menzies R, Turnour C, Chiu C, McIntyre P. Vaccine Preventable Diseases and Vaccination Coverage in Aboriginal and Torres Strait Islander People, Australia, 2003 to 2006. Commun Dis Intell 2008;32(Suppl):S2–S67.

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19. Singleton RJ, Hennessy TW, Bulkow LR, Hammitt LL, Zulz T, Hurlburt DA, et al. Invasive pneumococcal disease caused by nonvaccine serotypes among Alaska native children with high levels of 7-valent pneumococcal conjugate vaccine coverage. JAMA 2007;297(16):1784–1792.

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20. Mooney JD, Weir A, McMenamin J, Ritchie LD, Macfarlane TV, Simpson CR, et al. The impact and effectiveness of pneumococcal vaccination in Scotland for those aged 65 and over during winter 2003/2004. BMC Infect Dis 2008;8:53.

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25. Black S, Shinefield H, Fireman B, Lewis E, Ray P, Hansen JR, et al. Efficacy, safety and immunogenicity of heptavalent pneumococcal conjugate vaccine in children. Pediatr Infect Dis J 2000;19(3):187–195.

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27. Krause VL, Reid SJ, Merianos A. Invasive pneumococcal disease in the Northern Territory of Australia, 1994–1998 [erratum appears in Med J Aust 2001 Mar 19;174(6):309]. Med J Aust 2000;173(Suppl):S27–S31.

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29. Torzillo PJ, Hanna JN, Morey F, Gratten M, Dixon J, Erlich J. Invasive pneumococcal disease in central Australia. Med J Aust 1995;162(4):182–186.

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