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Other bacterial infections

Legionellosis, leprosy, meningococcal infection and tuberculosis were notifiable in all States and Territories in 2000 and in the NNDSS are grouped as 'other bacterial infections'. A total of 2,121 notifications were classified as other bacterial infections in 2000, which accounted for 2.3 per cent of all notifications. Notifications of other bacterial infections reported to the NNDSS are shown in Tables 26 and 27.

Table 26. Trends in notifications of other bacterial infections, Australia, 1991 to 2000*

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Legionellosis	119	208	170	178	161	208	157	262	249	472
Leprosy	14	20	17	10	10	7	12	3	6	4
Meningococcal infection	347	308	377	385	377	420	494	480	591	621
Tuberculosis	661	904	986	994	1093	978	989	960	1,143	1,024

* All jurisdictions reputed for all years

Table 27. Trends in notification rates of other bacterial infections, Australia, 1991 to 2000 (rate per 100,000 population)*

Disease	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000
Legionellosis	0.7	1.2	1.0	1.0	0.9	1.1	0.8	1.4	1.3	2.5
Leprosy	0.1	0.1	0.1	0.1	0.1	< 0.1	0.1	< 0.1	< 0.1	< 0.1
Meningococcal infection	2.0	1.8	2.1	2.2	2.1	2.3	2.7	2.6	3.1	3.2
Tuberculosis	3.8	5.2	5.6	5.6	6.0	5.3	5.3	5.1	6.0	5.3

* All jurisdictions reputed for all years

Legionellosis

Legionellosis is an acute bacterial infection with two clinical manifestations: Legionnaires' disease and Pontiac fever. Legionellosis describes a group of diseases caused by various species of Legionella as well as the pneumonia of classical Legionnaires' disease caused by Legionella pneumophila.

L. pneumophila occurs in water sources, and can tolerate a wide range of temperatures, pH and dissolved oxygen contents. Depending on favourable temperatures, sediment accumulation and the presence of commensal microflora, the bacteria can proliferate in cooling towers and water systems, despite chlorination. Inhalation of aerosols containing the bacteria is the major mode of transmission. The risk of infection with Legionella is increased by age, chronic lung disease, immunosuppression and cigarette smoking.⁸⁸

L. longbeachae has been recognised for some years as a frequent cause of Legionella pneumonia in Australia.^89,90 A study found that 26 of 45 Australian potting soils were tested positive for L. longbeachae, suggesting this route of exposure may be important in the epidemiology of sporadic legionellosis in Australia.^91,92

Legionellosis is notifiable in all the States and Territories in Australia, and includes notifications of infections caused by all Legionella species. There were 472 notifications of legionellosis in 2000 resulting in a notification rate of 2.5 cases per 100,000 population which has reached the highest level since 1991 (Figure 51). The seasonal trend showed a peak of 114 notifications in November 2000.

Top of pageFigure 51. Trends in notification rates of legionellosis, Australia, 1991 to 2000, by month of onset



The reporting rates of legionellosis were highest in South Australia (5.9 cases per 100,000 population) and Victoria (5.2 cases per 100,000 population) (Tables 2 and 3). Men accounted for 65 per cent of reported cases. Cases occurred in almost all age groups, with a peak in the 75-79 year age group for men (15.1 cases per 100,000 population) and the 65-69 year age group for women (6.4 cases per 100,000 population) (Figure 52).

Figure 52. Notification rates of Legionellosis, Australia, 2000, by age and sex



Data on the causative species were available for 448 (95%) of the legionellosis cases. Of these, 311 (69%) cases were identified as L. pneumophilia, followed by L. longbeachae (131 cases, 29%), L. micdadei (4 cases) and L. bozemannii (2 cases).

In 2000, there was a total of 22 deaths as the result of legionellosis reported by States or Territories. Victoria reported 12 deaths (11 cases of L. pneumophila and 1 case of L. micdadei), South Australia reported 5 deaths (3 cases of L. pneumophilia and 2 cases of L. longbeachae), New South Wales reported 3 deaths (2 cases of L. pneumophilia and 1 case of L. longbeachae) and Western Australia reported 2 deaths (species data unavailable).

Six outbreaks of legionellosis were identified in 2000 and all occurred in Victoria.^93,94,95 Australia's largest outbreak of legionellosis to date occurred in Melbourne in April 2000, with a total of 125 confirmed cases (J. Greig, Victoria Department of Human Services, personal communication). The outbreak was linked to the newly opened Melbourne Aquarium. Of the 125 cases, 110 occurred in visitors to the aquarium between 11 and 27 April, and the remainder were in people who were within 500m of the building. During this time period 83,500 people visited the tourist attraction, giving a crude attack rate of 0.13 per cent.

The median age of cases was 64 years, and 57 per cent were male. Of the cases, 76 per cent were hospitalised for an average of 12.8 days, and 17 per cent of cases required admission to intensive care at some time during their hospital stay. The overall case fatality rate was 3.2 per cent, including 2 aquarium visitors and 2 people who were in the vicinity during the risk period. Most cases (83%) were diagnosed by urinary antigen test for L. pneumophila serogroup 1. Use of the urinary antigen test for early diagnosis of cases and rapid public health action probably contributed to relatively low morbidity and case fatality rates.

Of the remaining 5 outbreaks identified in Australia in 2000, four were in metropolitan Melbourne and one was in rural Victoria. A total of 28 cases were involved in these 5 outbreaks.⁹⁵

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Leprosy

Leprosy is a chronic infection of 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.

There were 4 cases of leprosy notified nationally in 2000 compared with six in 1999. Two of the cases in 2000 occurred in New South Wales with one each in Queensland and South Australia. Of the 4 cases, one was male and three were female and the age range was 20-59 years. Information on country of birth was available for 3 cases, one was born in India, one in the Philippines and another in Viet Nam.

Invasive meningococcal disease

Neisseria meningitidis the one cause of bacterial meningitis. Worldwide, invasive meningococcal disease accounts for at least 500,000 cases and 50,000 deaths per annum. Many of these occur in the sub-Sahara Africa 'meningitis belt'. Serogroups B and C are the major cause of both sporadic and epidemic meningococcal disease in industrialised countries, including Australia, while serogroups Y and W-135 are uncommon. In contrast, serogroup A is mainly associated with the pandemic of meningococcal disease in Africa.^96,97 New Zealand has experienced an on-going epidemic of meningococcal disease associated with serogroup B since 1991 which peaked at 16.9 cases per 100,000 population in 1997. The average rate for the period 1996 to 2000 was 13.9 cases per 100,000 population.⁹⁸

Four distinct clinical situations are associated with meningococcal infection; asymptomatic nasopharyngeal colonisation, benign bacteraemia, meningitis and meningococcemia. The organism is carried in the nose of up to 5-10 per cent of the population. A small minority of those colonised will progress to invasive disease. Meningococcal meningitis is the most common pathologic presentation, especially during epidemics. Meningococcal septicaemia is the most severe form of infection and has a high fatality rate.⁹⁹

In Australia, there were 621 notifications of invasive meningococcal disease nationally in 2000. The annual notification rate of 3.2 cases per 100,000 population is the highest rate since 1991 (Figure 53). Of the total, 471 (75.8%) cases were culture-confirmed. Of these, 274 (58.2%) were serogroup B, 173 (36.7%) were serogroup C, 11 (2.3%) were serogroup W-135 and 13 (2.8%) were serogroup Y. Although serogroup B remains the predominant serogroup among the notifications, notifications of serogroup C have increased steadily during the period (Table 28).

Figure 53. Trends in notification rates of invasive meningococcal infection, Australia, 1991 to 2000, by month of onset



Table 28. Proportion of major serogroup of meningococcal notifications, 1995 to 2000

Year	B		C		Non B, Non C		Total
	n	%	n	%	n	%
1995	31	8.1	15	4.0	335	87.9	381
1996	155	36.8	85	20.2	181	43.0	421
1997	96	19.8	57	11.8	331	68.4	484
1998	139	30.7	83	18.3	231	51.0	453
1999	212	37.3	143	25.2	213	37.5	568
2000	274	44.1	173	27.8	174	28.0	621

In 2000, the pattern of seasonal variation in meningococcal notifications continued, with the greatest number of cases occurring in late Winter or early Spring (Figure 53). The distribution of notifications by age shows the highest peak in children aged 0-4 years (15.8 cases per 100,000 population) and an additional peak in the 15-24 year age range (8.7 cases per 100,000 population) (Figure 54). The overall male to female ratio was 1.1:1.

Top of pageFigure 54. Notification rates of invasive meningococcal infection, Australia, 2000, by age and sex



Forty-one deaths from meningococcal infections were reported in 2000, including 14 deaths in New South Wales, 13 deaths in Victoria, 6 deaths in Western Australia, 4 deaths in Queensland and 2 deaths in both South Australia and Tasmania. There were no major outbreaks of invasive meningococcal infection reported, and only three pairs of linked cases were identified.

The notification rate for meningococcal disease has been slowly, but consistently increasing over the past 10 years from 1.8 cases per 100,000 population in 1992 to 3.2 cases per 100,000 population in 2000 (Figure 53). It was suggested that the increase of meningococcal disease in Australia has been primarily due to the expansion of virulent phenotypes of serogroups B and C.^{100,101,102,103} In addition, the case definition has been changed in some jurisdictions to include suspected cases and expanded laboratory diagnosis methods.¹⁰⁴ Despite rising public awareness and improvements in personal and environmental health measures, meningococcal disease remains the major life-threatening infection for children and adolescents in Australia.

Laboratory based meningococcal surveillance

The Australian Meningococcal Surveillance Programme annual report for 2000¹⁰⁵ summarised the phenotype and antibiotic susceptibility of Neisseria meningitidis from invasive cases of meningococcal disease. In 2000, a total of 388 isolates were examined by the National Neisseria Network laboratories, the highest number of isolates since the inception of the program in 1994.

Of the 388 isolates typed, serogroup B still predominated nationally (217 type B; 56% of total) and in all the jurisdictions, except Victoria. This was followed by serogroup C (143 isolates; 37% of total), serogroup Y (13 isolates; 3.2%) and serogroup W-135 (9 isolates; 2.3%). Serogroup C was the major serogroup in Victoria (58 isolates, 53.7% of total). Nationally the proportion of serogroup B of all strains was lower than in the previous 3 years. Phenotypes C:2a:P1.4(7), C:2a:P1.2 and C:2a:P1.5 were first isolated in Australia in 1999. Phenotypes C:2a:P1.4(7) and C:2a:P1.2 were still commonly isolated in Victoria in 2000, but were occasionally encountered in other jurisdictions. Phenotype C:2a:P1.5 remained common in New South Wales. About two-thirds of all isolates showed decreased susceptibility to the penicillin group of antibiotics (MIC 0.06 to 0.5 mg/L). All isolates tested were susceptible to third generation cephalosporins and to the prophylactic agents rifampicin and ciprofloxacin.

In 2000, the number of non-culture diagnoses of invasive meningococcal disease were increased to 147 cases from 92 cases in 1999. Of the147 cases, 91 tested positive by PCR positive, 49 were positive by serology only and 7 tested positive by both PCR and serology.

Data on outcome (whether the patient survived or died) were available for 278 patients (71%). Of the 278, 25 (9%) patients died as a result of their infection. There were 13 deaths among cases with serogroup C infection, 9 deaths of serogroup B infection, 2 deaths of serogroup Y and 1 death of serogroup W-135.

Tuberculosis

There are three national surveillance systems for tuberculosis. The NNDSS provides the timeliest information on national TB notifications. The National Mycobacterial Surveillance System (NMSS), a surveillance system dedicated to tuberculosis and atypical mycobacterial infections, provides more detailed information on risk factors, diagnostic methods, drug therapy and relapse status.¹⁰⁶ The Australian Mycobacterial Reference Laboratory Network maintains national data on drug susceptibility profiles, site of disease, age, sex and laboratory method of diagnosis for all mycobacterial isolates. These data are published annually in conjunction with the NMSS surveillance report.¹⁰⁷

In 2000, 1,024 TB notifications were received by the NNDSS, giving a reporting rate of 5.3 cases per 100,000 population. The highest rate was reported in the Northern Territory (22.0 cases per 100,000 population), followed by New South Wales (6.8 cases per 100,000 population) and Victoria (6.0 cases per 100,000 population).

There was little difference in notifications between the gender, with a male to female ratio of 1.1:1. While cases have occurred in all age groups, most cases occurred in the 20-24 year age group and older. The highest age-specific rates were in men in the 80-84 year age group (19.5 cases per 100,000 population) and in women in the 25-29 year age group (8.7 cases per 100,000 population).


This article was published in Communicable Diseases Intelligence Volume 26, No 2, June 2002