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Other bacterial infections

Legionellosis, leprosy, invasive meningococcal infection and tuberculosis (TB) were notifiable in all states and territories in 2001 and classified as 'other bacterial infections' in NNDSS. A total of 1,978 notifications were classified in this group in 2001, which accounted for 1.9 per cent of all the notifications to NNDSS.

Legionellosis

Legionellosis is an acute infection caused by various species of Legionella bacteria with two clinical manifestations: Legionnaires' disease and Pontiac fever. Legionnaires' disease, caused commonly by Legionella pneumophila, is a severe form of pneumonia, which may be accompanied by involvement of other organs such as the brain, the bowel and the kidneys. Symptoms include a rapid onset of high fever, a non-productive cough, chills, headache and general malaise. Diagnosis is based on isolating and identifying Legionella pneumophila from the patient's respiratory secretions or blood. The incubation period is usually 2-10 days. Less than five per cent of exposed persons become ill, but up to 30 per cent of those who become ill may die, depending on the population.¹⁶

Legionellosis is notifiable in all the states and territories of Australia, and includes notifications of infections caused by all Legionella species. The annual rates since 1991 show a marked increase in notifications in 2000 (Figure 64), because of the Melbourne aquarium outbreak.¹⁰² This was followed in 2001 by a decrease in notifications, but the number was still greater than those in years prior to 2000. A recent analysis of national legionellosis notification data showed a significant increase between 1991 and 2000, even when outbreak cases were excluded.¹⁰³

Figure 64. Trends in notification rates of legionellosis, Australia, 1991 to 2001, by year of onset



There were 307 notifications of legionellosis reported in 2001, giving a national rate of 1.6 cases per 100,000 population. The highest rates of legionellosis were reported in Victoria (2.5 cases per 100,000 population) and Western Australia (2.2 cases per 100,000 population). Legionellosis notifications showed a peak in reports in autumn and spring.

Men accounted for 209 of the 307 (68 %) cases of legionellosis in 2001, to give a male to female ratio of 2.1:1. The highest rates were in the 80-84 year age group for men (10.1 cases per 100,000 population) and the 85 year and over age group for women (4.3 per 100,000 population, Figure 65).

Top of pageFigure 65. Notification rates of legionellosis, Australia, 2001, by age group and sex



Data on the causative species was available for 286 (93%) of the legionellosis cases. Of these, 152 (52%) were identified as L. longbeachae, 131 (46%) as L. pneumophilia, and three (1%) as other species (Table 20). In 2001 the proportion of L. pneumophila causing legionellosis cases was significantly higher in Victoria (109/121, 90%) than in the rest of the Australia (22/186, 12%, chi-square =180, p<0.0001).

Table 20. Notifications of legionellosis, Australia, 2001, by species and state or territory

State or territory	Species of Legionella				Total
	L. longbeachae	L. pneumophila	Other species*	Unknown
ACT	2	0	0	0	2
NSW	63	0	0	4	67
NT	3	0	0	0	3
Qld	17	15	0	5	37
SA	29	3	0	0	32
Tas	1	1	0	1	3
Vic	6	109	3	3	121
WA	31	3	0	8	42
Total	152	131	3	21	307

* Other includes L. micdadei and L. bozemannii.

There were 12 deaths identified as due to legionellosis in Australia in 2001, giving a case fatality rate of 3.9 per cent. The breakdown of deaths by state and territory and infecting Legionella species is shown in Table 21. The case fatality rate for infections with L. pneumophila (11/131, 8.4%) was significantly higher than the case fatality rate for L. longbeachae infections (1/152, 0.6%, chi-square=8.5, p<0.005).

Table 21. Deaths due to legionellosis, Australia, 2001, by species and state or territory

State or territory*	Species of Legionella				Total
	L. longbeachae	L. pneumophila	Other species†	Unknown
ACT	0	0	0	0	0
NT	0	0	0	0	0
Qld	0	1	0	0	1
SA	1	1	0	0	2
Tas	0	0	0	0	0
Vic	0	8	0	0	8
WA	0	1	0	0	1
Total	1	11	0	0	12

* No data available for New South Wales.
† Other includes L. micdadei and L. Bozemannii.

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Leprosy

Leprosy is a chronic infection of the skin and peripheral nerves with Mycobacterium leprae. Despite elimination from most countries, the disease remains a major endemic public health problem in six countries. One of these, India, accounts for 64 per cent of prevalent infections and 78 per cent of incident cases worldwide.¹⁰⁴ In Australia, leprosy is a rare disease, with the majority of cases occurring in migrants from leprosy-endemic countries or Indigenous communities.

In 2001, five leprosy cases were notified, compared with four in 2000. Three of the five cases occurred in New South Wales and two in Western Australia. Of these, four were male and one female, and the age range was 18-48 years. The country of birth was known for all five cases, and only one was born overseas, in Vietnam. Among the four Australian-born cases, three were identified as Indigenous Australians (two from Western Australia; one from New South Wales), while the Indigenous status of the fourth was not stated.

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Invasive meningococcal disease

The meningococcus (Neisseria meningitidis) is an asymptomatic nasopharyngeal colonising organism found in 25 to 50 per cent of the general population. Invasive infection, however, can cause severe clinical meningitis, which has a high fatality rate.¹⁰⁵ Children, adolescents and the elderly are most at risk of this form of infection.

Meningococcal serogroups A, B, C, Y and W-135 are the main human pathogens. In Australia, serogroups B and C are the major causes of invasive meningococcal disease. WHO estimated that, internationally, there are at least 500,000 cases of invasive meningococcal disease and 50,000 deaths from the disease every year.¹⁰⁶

The annual notification rate for meningococcal disease has been increasing in Australia over the past 10 years (Figure 66). In 2001, there were 677 notifications giving a national notification rate of 3.5 cases per 100,000 population, a slight increase from the 622 cases and rate of 3.2 cases per 100,000 population reported in 2000.

Figure 66. Trends in notification rates of invasive meningococcal infection, Australia, 1992 to 2001, by year of onset



The largest number of cases in 2001 occurred in late winter (August, n=93) and early spring (September, n=81). The highest age specific rate was in children in the 0-4 year age group (16.3 cases per 100,000 population) and in the 15-19 year age group (7.8 cases per 100,000 population). Rates according to age group and sex are shown in Figure 67. More cases occurred among male children aged less than five years, and the male to female ratio was 2.6:1.

Figure 67. Notification rates of invasive meningococcal infection, Australia, 2001, by age group and sex



Among 677 meningococcal cases, 452 (67%) had the serogroup identified. Of these, serogroup B occurred in 283 (63%), 155 (34%) were serogroup C and 14 (3%) were serogroup W135 or Y (Table 22).

Top of pageTable 22. Notifications of invasive meningococcal infection by serogroups, 2001, by state or territory

Jurisdiction	Meningococcal serotype				Total
	Serogroup B	Serogroup C	Serogroups A, Y or   W	Unknown serogroup
ACT	2	0	0	4	6
NSW	85	35	4	106	230
NT	10	2	0	1	13
Qld	67	32	6	22	127
SA	22	7	1	9	39
Tas	5	17	0	1	23
Vic	47	56	2	58	163
WA	45	6	1	24	76
Total	283	155	14	225	677

In 2001 there were 43 deaths due to meningococcal disease giving a crude case fatality rate of 6.3 per cent. The breakdown of deaths by state and territory and serogroup are shown in Table 23. Meningococcal serogroup C disease was associated with a significantly higher case fatality rate (23/155, 14.8%) than serogroup B disease (16/283, 5.6%, chi-square=9.3, p<0.005).

Table 23. Deaths due to invasive meningococcal infection by serogroups, 2001, by state or territory

Jurisdiction	Meningococcal serotype				Total
	Serogroup B	Serogroup C	Serogroup A, Y or W	Unknown serogroup
ACT	0	0	0	0	0
NSW	2	5	0	0	7
NT	1	1	0	0	2
Qld	4	5	0	2	11
SA	2	1	0	0	3
Tas	1	4	0	0	5
Vic	2	7	0	2	11
WA	4	0	0	0	4
Total	16	23	0	4	43

There were a number of linked cases of meningococcal disease in 2001 in all jurisdictions except the Northern Territory, where all cases were sporadic. A pair of linked cases in Queensland prompted the vaccination and chemoprophylaxis of more than 2,000 contacts. In Western Australia, four cases of serogroup B invasive meningococcal disease occurred over a period of 10 months in an Aboriginal community in an outer metropolitan area. These cases occurred in November 2000, and February, late July and early August 2001, in children aged between two and nine years. On each occasion, appropriate public health actions, including contact tracing and provision of advice and chemoprophylaxis to identified household and other close contacts, were performed. Mass chemoprophylaxis was provided to all residents of the community and regular visitors to it. There have been no further cases following these interventions.

A large outbreak of 14 cases of serogroup C (phenotype 2a:P1.5,2) occurred in southern Tasmania. In response, antibiotic prophylaxis was offered to contacts of cases and intensified surveillance, through laboratory and clinical services, was carried out. Regular press conferences were also held, in which the importance of early detection and empirical treatment were emphasised. General practitioners, pharmacists and schools were also alerted more directly to relevant disease information. A further two cases of serogroup C occurred in northern Tasmania, but these were shown to be due to a different phenotype.

The Australian Meningococcal Surveillance Programme was established in 1994 for the purpose of monitoring drug resistance in Neisseria meningitidis isolates causing 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 quantitatively determine the susceptibility of N. meningitidis to a core group of antibiotics. The results of the surveillance in 2001 have recently been published.¹⁰⁷ In 2001 about two-thirds of all the isolates showed decreased susceptibility to the penicillin group of antibiotics (MIC 0.06-0.5 mg/L), but all isolates tested were susceptible to third generation cephalosporins.

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Tuberculosis

TB is an infectious disease caused by Mycobacterium tuberculosis. The disease commonly affects the lungs and is usually transmitted person-to-person by airborne droplets.

Australia has one of the lowest rates of TB in the world, with most cases occurring in overseas-born and Indigenous Australians. The Federal Minister for Health and Ageing recently launched The National Strategic Plan for Tuberculosis Control in Australia Beyond 2000, prepared by the National Tuberculosis Advisory Committee. The plan consists of three key elements: case finding; treatment; and surveillance. Performance indicators have been developed to allow a regular review of the progress of the Strategic Plan.

In 2001, 989 TB notifications were received by NNDSS, a rate of 5.1 cases per 100,000 population. The notification rates of TB were lower than the national average in the Australian Capital Territory, Queensland, South Australia, Tasmania and Western Australia. The highest rate was reported in the Northern Territory (17.5 cases per 100,000 population).

In 2001, the male to female ratio was equal as it has been in the previous years. TB cases occurred in all age groups, with the highest age-specific rates reported in the 85 years and over age group for both males (29.3 cases per 100,000 population) and females (11.4 cases per 100,000 population) (Figure 68). Detailed analyses of TB in Australia have recently been published.¹⁰⁸

Figure 68. Notification rates of tuberculosis Australia, 2001, by age group and sex




This article was published in Communicable Diseases Intelligence Volume 27, No 1, March 2003.