Results

Other bacterial infections

Legionellosis, leprosy, meningococcal infection and tuberculosis were notifiable in all states and territories in 2006 and classified as 'other bacterial infections' in NNDSS. A total of 1,900 notifications were included in this group in 2006, which accounted for 1.37% of all the notifications to NNDSS, a similar total and proportion as in 2005 (1,826 notifications and 1.4% of total).

Legionellosis

Case definition – Legionellosis Both confirmed cases and probable cases are reported. Confirmed case: Requires isolation of Legionella, OR the presence of Legionella urinary antigen OR seroconversion or a significant increase in antibody level or a fourfold or greater rise in titre to Legionella, AND fever or cough or pneumonia. Probable case: Single high titre antibody titre to Legionella, OR detection of Legionella by nucleic acid testing, OR detection of Legionella by direct fluorescence assay, AND fever or cough or pneumonia.

Legionellosis includes notifications of infections caused by all Legionella species. There were 348 notifications of legionellosis reported in 2006, giving a national rate of 1.7 cases per 100,000 population. This was an increase over the 334 cases reported in 2005. In 2006, an increase in cases was seen in Western Australia (4.4 cases per 100,000 population, 91 cases) and South Australia (4.2 cases per 100,000 population, 65 cases).

Legionellosis notifications showed a peak in autumn and spring, as in previous years (Figure 72). Rates of legionellosis have ranged between 0.8 and 2.6 cases per 100,000 population between 1999 and 2005, except in 2000, when rates reached 6.9 cases per 100,000 population as a result of the Melbourne aquarium outbreak with 125 cases.⁴²

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Figure 72. Trends in notification rates of legionellosis, South Australia, Western Australia and Australia, 2002 to 2006, by month of onset

In 2006, men accounted for 222 of the 348 notified cases of legionellosis resulting in a male to female ratio of 1.7:1. There were no cases in children under the age of 15 years. Overall, the highest rate of infection was 8.5 cases per 100,000 population in the 80–84 years age group. In men, the highest rate occurred in men in the 75–79 years age group (12.1 cases per 100,000 population, 31 cases) and women, in the 80–84 years age group (7 cases per 100,000 population, 17 cases, Figure 73).

Figure 73. Notification rate of legionellosis, Australia, 2006, by age group and sex

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Data on the causative species were available for 336 (97%) of the 348 legionellosis cases. Of these, 178(53%) were Legionella longbeachae, 154 (46%) cases were identified as L. pneumophila and 4 (1%) were L. micdadei or L. bozemanii (Table 18).

Table 18. Notifications of legionellosis, 2006, by state or territory and species

Species	State or territory
	ACT	NSW	NT	Qld	SA	Tas.	Vic.	WA	Australia
Legionella longbeachae	0	22	2	7	46	2	13	86	178
Legionella pneumophila	1	54	1	26	18	1	51	2	154
Other species*	0	0	0	0	1	0	3	0	4
Unknown species	0	1	0	6	0	0	2	3	12
Total	1	77	3	39	65	3	69	91	348

* Legionella micdadei, Legionella bozemanii

Of the 154 L. pneumophila notifications, serogroup data were available on 83 (54%) cases; 77 (92%) of serogrouped L. pneumophila were serogroup 1.

There are significant differences in the geographic distribution of L. longbeachae and L. pneumophila, with the L. longbeachae making up the majority of species in notifications from South Australia and Western Australia, while L. pneumophila are the most common infecting species in the eastern states (Queensland, New South Wales and Victoria).

Data on the death of legionellosis cases were available for 230 (66%) notifications. There were 9 reported deaths due to legionellosis in Australia in 2006, giving a case fatality rate of 3.9%. The break down of deaths by state or territory and infecting Legionella species is shown in Table 19. There were 6 deaths associated with L. longbeachae infection (all in Western Australia) giving a case fatality rate of 3.3%. Three patients with L. pneumophila infections died, giving a case fatality rate of 1.9%. Case fatality rates may be overestimated given the large proportion of cases without details of death outcomes.

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Table 19. Deaths due to legionellosis, Australia, 2006, by state or territory and species

Species	State or territory
	ACT	NSW	NT	Qld	SA	Tas.	Vic.	WA	Australia
Legionella longbeachae	0	0	0	0	0	0	0	6	6
Legionella pneumophila	0	0	0	0	1	0	2	0	3
Other species*	0	0	0	0	0	0	0	0	0
Unknown species	0	0	0	0	0	0	0	0	0
Total	0	0	0	0	1	0	2	6	9

* Legionella micdadei, Legionella bozemanii

The number of deaths decreased in 2006 relative to 2005 when there were 14 deaths. Decreases in deaths associated with legionellosis fell in all states and territories except Western Australia where there were 3 more deaths in 2006 than in 2005.

There were 3 outbreaks of legionellosis was reported in 2006. A cluster of 10 cases (including 1 death) was linked to a Melbourne metropolitan shopping centre. In Sydney, 6 linked cases were reported, while in Queensland a cluster of cases associated with a coal mine was also reported.

A case control study of L. longbeachae cases in South Australia was recently published, which clarified risk factors associated with this infection.⁴³ The organism has been isolated from potting mix 44 and inhalation of dust from potting mix has been thought to be a major route of infection. The recent study by O'Connor⁴³ demonstrated that other risk factors such as exposure to aerosolised bacteria from dripping hanging pots and possible ingestion of organisms due to failure to wash hands after gardening may be more significant. Long-term smokers were also shown to be at increased risk of infection.⁴³

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Leprosy

Case definition – Leprosy Only confirmed cases are reported. Confirmed case: Requires demonstration of acid fast bacilli in split skin smears and biopsies prepared from ear lobe or other relevant sites or histopathological report from skin or nerve biopsy compatible with leprosy (Hansen's disease) examined by an anatomical pathologist or specialist microbiologist AND compatible nerve conduction studies or peripheral nerve enlargement or loss of neurological function not attributable to trauma or other disease process, or hypopigmented or reddish skin lesions with definite loss of sensation.

Leprosy is a chronic infection of the skin and peripheral nerves with the bacterium Mycobacterium leprae. Leprosy is a rare disease in Australia, with the majority of cases occurring among migrants to Australia from leprosy endemic countries and occasional cases from Indigenous communities. Trends in the numbers of leprosy notification in Indigenous and non-Indigenous Australians and the overall rate are shown in Figure 74.

Figure 74. Number of notifications of leprosy in Indigenous and non-Indigenous Australians and the overall notification rate, 1991 to 2006

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In 2006, 5 leprosy cases were notified to NNDSS compared with 10 cases in 2005. There were 2 cases in Western Australia, and a single case in New South Wales, the Northern Territory and South Australia. Two cases occurred in men and 3 in women. None of the cases were Indigenous Australians. The age range of cases was 26–42 years. Four of the 5 cases had multi-bacillary leprosy.

Invasive meningococcal disease

Case definition – Invasive meningococcal disease Both confirmed cases and probable cases are reported. Confirmed case: Defined as isolation of Neisseria meningitidis from a normally sterile site. Alternatively, detection of meningococcus by nucleic acid testing, or Gram negative diplococci in Gram stain in specimens from a normally sterile site or from a suspicious skin lesion, OR high titre IgM or a significant rise in IgM or IgG titres to outer membrane protein antigens, OR positive polysaccharide antigen test in cerebrospinal fluid AND disease compatible with invasive meningococcal disease. Probable case: Defined as 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.

Historically in Australia, serogroups B and C have been the major cause of invasive meningococcal disease. The Australian Government commenced the National Meningococcal C Vaccination Program in January 2003.

In 2006, there were 318 notifications of invasive meningococcal disease in Australia, a decrease from 392 in 2005. A decline was seen in all states except South Australia and Victoria. The total in 2006 was the lowest since 1996. The national notification rate in 2006 was 1.5 cases per 100,000 population. The highest rate was reported from the Northern Territory (2.9 cases per 100,000 population, 6 cases).

Fifty-two per cent (165) of cases occurred in males, giving a male to female ratio of 1.1:1. As in previous years, the largest number of cases occurred in winter and spring (Figure 75). The majority of cases (294, 93%) were confirmed, and 24 (7%) had a probable diagnosis.

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Figure 75. Trends in notification rates of meningococcal infection, Australia, 2002 to 2006, by month of onset and serogroup

Of the 318 meningococcal notifications in 2006, 267 (84%) were serogrouped. Of these, 223 (83.5%) were serogroup B, 24 (9%) were serogroup C and 20 (7.5%) were infections with serogroup Y (5), serogroup W-135 (14) or serogroup A (1) (Table 20). In comparison in 2005, 83% (326/393) of notified cases were serogrouped, 256 (79%) were serogroup B and 46 (14%) were serogroup C.

Table 20. Notifications of meningococcal infection, 2006, by state or territory and serogroup

Species	State or territory
	ACT	NSW	NT	Qld	SA	Tas.	Vic.	WA	Australia
Serogroup B	4	57	6	58	14	4	62	18	223
Serogroup C	1	14	0	4	0	1	3	1	24
Other serogroups*	0	6	0	3	3	0	7	1	20
Unknown serogroup	0	30	0	6	1	0	13	1	51
Total	5	107	6	71	18	5	85	21	318

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* Serogroup Y (5 cases); serogroup W-135 (14 cases) and serogroup A (1 case).

Serogroup C infections were largely confined to the eastern seaboard states; Victoria, New South Wales and Queensland, where serogroup C meningococcal disease has in previous years been more common than in other states.

The highest age specific meningococcal notification rate was in children aged 0–4 years with a rate of 8.8 cases per 100,000 population (112 cases). Eighty-four per cent of cases (94/112) were serogroup B infections, which is the highest age-specific rate for serogroup B infection, with 7.3 cases per 100,000 population.

In the 15–19 years age group, the overall rate of meningococcal infection was 3.9 cases per 100,000 population (55 cases), 42 (76%) of which were serogroup B (Figure 76).

Figure 76. Notification rate of meningococcal C infection, Australia, 2000 to 2006, by age group

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There has been a marked decrease in meningococcal C infection rates since 2003 when the National Meningococcal C Vaccination Program was introduced. In 2006, coverage meningococcal serogroup C vaccines in children aged 12 months reached 92.5% of Indigenous children and 93.4% of non-Indigenous children (data provided by the Australian Childhood Immunisation Register).

The greatest declines in the rate of serogroup C disease was in the 15–19 years age group from 6.6 cases per 100,000 population in 2002 (63 cases) to 0.3 cases per 100,000 population in 2006 (3 cases). The rate in the 20–24 years age group fell from 2.6 (35 cases) to 0.4 (6 cases) over the same period. Notification rates in the 0–4 years age group fell from 2.2 cases per 100,000 population in 2001 (28 cases) to 0.2 cases per 100,000 population (4 cases) in 2006.

Figure 77 shows that over the period 2001 to 2006 notification rates of serogroup B disease have declined in the 0–4 years age group by 21%; in the 5–9 years age group by 45%; and in the 10–14 years age group by 80%, while remaining stable in older age groups.

Figure 77. Notification rate of meningococcal B infection, Australia, 2001 to 2006, by age group

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There were 12 deaths due to meningococcal disease in 2006 (a case fatality rate of 3.7%). Eight deaths were due to serogroup B (CFR= 3.6%), 3 due to W-135 (CFR = 21%) and only 1 death was due to serogroup C disease (CFR = 4.2%, Table 21). This was a decrease on the 20 deaths in 2005.

Table 21. Deaths due to meningococcal infection, Australia, 2006, by state or territory and serogroup

Species	State or territory
	ACT	NSW	NT	Qld	SA	Tas.	Vic.	WA	Australia
Serogroup B	0	3	0	2	1	0	2	0	8
Serogroup C	0	1	0	0	0	0	0	0	1
Serogroup W-135	0	1	0	0	0	0	2	0	3
Total	0	5	0	2	1	0	4	0	12

In contrast to previous years, there were only a few reports of small clusters of meningococcal disease (all serogroup B) in 2006. A case of meningococcal serogroup A on a passenger airline prompted a multi-state and international follow-up of potentially exposed fellow passengers. No secondary cases were reported.

Laboratory based meningococcal surveillance

The Australian Meningococcal Surveillance Programme (AMSP) was established in 1994 for the purpose of monitoring and analysing isolates of Neisseria meningitidis from cases of invasive meningococcal disease in Australia. The program is undertaken by a network of reference laboratories in each state and territory, using agreed standard methodology to determine the phenotype (serogroup, serotype and serosubtype) and the susceptibility of N. meningitidis to a core group of antibiotics. The results of laboratory surveillance in 2006 have recently been published.⁴⁵

In 2006, a total of 271 laboratory confirmed cases of invasive meningococcal disease were examined by the AMSP. Consistent with the NNDSS data, the AMSP reported that 80% were identified as serogroup B (217) and 9.6% were serogroup C (26). No evidence of meningococcal capsular 'switching' was detected. About two-thirds of all isolates showed decreased susceptibility to penicillin (MIC 0.06–0.5 mg/L). All isolates remained susceptible to rifampicin and ciprofloxacin.

The changing ecology of meningococcal disease in Australia has been recently reviewed.⁴⁶ The 'hyper-sporadic' period since the 1980s when hyper-virulent serogroup B and serogroup C clones dominated and incidence remained above 2 cases per 100,000 population, may be changing as the impact of the conjugate serogroup C meningococcal vaccine reduces the incidence of serogroup C disease.⁴⁷

Tuberculosis

Case definition – Tuberculosis Only confirmed cases are reported. Confirmed case: Defined as of Mycobacterium tuberculosis complex by culture, OR detection of M. tuberculosis complex by nucleic acid testing except which it is likely to be due to previously treated or inactive disease OR clinical diagnosis of tuberculosis including clinical follow-up assessment to ensure a consistent clinical course.

While Australia has one of the lowest rates of tuberculosis in the world, the disease remains a public health problem in the overseas-born and Indigenous communities. In 2006, 1,229 TB notifications were received by NNDSS, a rate of 6 cases per 100,000 population compared with 1,083 cases notified nationally 2005. The notification rate of TB was higher than the national average in the Northern Territory (15 cases per 100, 000 population), while the lowest rate occurred in Tasmania (1.8 cases per 100, 000 population). Further details of TB notifications in 2006 have already been published.⁴⁸

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