Methods

Australia is a federation of 6 states (New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Australia) and 2 territories (the Australian Capital Territory and the Northern Territory).

State and territory health departments collect notifications of communicable diseases under their public health legislation. In September 2007, the National Health Security Act 2007¹ received royal assent. This Act provides a legislative basis for and authorises the exchange of health information, including personal information, between jurisdictions and the Commonwealth. The Act provides for the establishment of the National Notifiable Diseases List,² which specifies the diseases about which personal information can be provided. The National Health Security Agreement,³ which was drafted in 2007 and signed by Health Ministers in April 2008, establishes operational arrangements to formalise and enhance existing surveillance and reporting systems, an important objective of the Act. In 2007, states and territories voluntarily forwarded de-identified data on 65 nationally agreed communicable diseases to the Department of Health and Ageing for the purposes of national communicable disease surveillance, although not all 65 were notifiable in each jurisdiction. Data were electronically renewed daily or several times a week from states and territories. The system was complemented by other surveillance systems, which provided information on various diseases, including four that are not reported to the National Notifiable Diseases Surveillance System (NNDSS) (HIV, AIDS and the classical and variant forms of Creutzfeldt-Jakob disease).

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In 2007, the NNDSS core dataset included the following 5 mandatory data fields: unique record reference number; notifying state or territory; disease code; confirmation status and the date when the public health unit was notified (notification receive date). In addition, the following core but non-mandatory data fields were supplied where possible: date of birth; age at onset; sex; indigenous status; postcode of residence; disease onset date; date when the medical practitioner signed the notification form (notification date), death status, date of specimen collection and outbreak reference number (to identify cases linked to an outbreak). Where relevant, information on the species, serogroups/subtypes and phage types of organisms isolated, and on the vaccination status of the case were collected and reported to NNDSS. Data quality was monitored by the Office of Health Protection and the National Surveillance Committee (NSC), a jurisdictional committee comprised of surveillance and data managers. There was a continual process of improving the national consistency of communicable disease surveillance through the daily, fortnightly and quarterly review of these data.

While not included in the core national dataset, enhanced surveillance information for some diseases (invasive pneumococcal disease, hepatitis C, tuberculosis and some sexually transmissible infections) was reported from states and territories to NNDSS but are not included in this report. Additional information concerning mortality and specific health risk factors for some diseases were obtained from states and territories and included in this annual report.

Newly diagnosed HIV infection and AIDS were notifiable conditions in each state or territory health jurisdiction in 2007 and were forwarded to the National HIV Registry and National AIDS Registry at the National Centre in HIV Epidemiology and Clinical Research (NCHECR). Further information can be found in NCHECR's annual surveillance report.⁴

The surveillance for the classical and variant forms of Creutzfeldt-Jakob disease (CJD) in Australia is conducted through the Australian National Creutzfeldt-Jakob Disease Registry (ANCJDR) since its establishment in October 2003. CJD is a nationally notifiable disease and by June 2006, CJD was notifiable in all states and territories. Further surveillance information on CJD can be found in surveillance reports from the ANCJDR.⁵

Information from communicable disease surveillance is communicated through several avenues. The most up-to-date information on topics of interest is provided at fortnightly teleconferences of the Communicable Diseases Network Australia (CDNA) and a summary of these reports is available online from http://www.health.gov.au/cdnareport.⁶ The Communicable Diseases Intelligence (CDI) quarterly journal publishes surveillance data and reports of research studies on the epidemiology and control of various communicable diseases. CDI is also available online from http://www.health.gov.au/cdi

Notification rates for each notifiable disease were calculated using the estimated 2007 mid-year resident population supplied by the Australian Bureau of Statistics⁷ (ABS) (Appendix 1 and Appendix 2). Where diseases were not notifiable in a state or territory, national rates were adjusted by excluding the population of that jurisdiction from the denominator. For some diseases, age adjusted rates were calculated using either the direct method of standardisation for gastrointestinal diseases, or indirect method for sexually transmissible infections, with 2001 census data as the standard population.

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The geographical distribution of selected diseases was mapped using ArcGIS (ESRI, Redlands, CA) software in conjunction with the Australian Standard Geographical Classification.⁸ Maps were based on the postcode of residence of each notification aggregated to the appropriate Statistical Division⁹ (SD) (Map 1, Table 1). The Northern Territory was represented by Statistical Subdivisions.⁹ Some individual postcodes were used for a multitude of disparate localities. These postcodes were generally in close proximity to each other and contained within the same Statistical Division (95.5% of all postcodes). However a small number of postcodes (n=113) were scattered throughout neighbouring Statistical Divisions. ABS concordance files were used to proportionally allocate notifications into SDs according to the percentage of the population of that postcode unit living in the SD.¹⁰ For instance, the postcode 2406 can be found in 2 distinct SDs, Northern (130) and South West (325). Almost 81% of the population live in Northern so this SD will get 81% of the notifications that have a postcode of 2406.

Map 1: Australian Bureau of Statistics Statistical Division codes, Australia, and Statistical Subdivision codes, the Northern Territory, 2007

Table 1: Australian population by Statistical Division and Statistical Subdivision for the Northern Territory, 2007

SD code	Statistical Division	Population	SD code	Statistical Division	Population
Australian Capital Territory			South Australia
805	Canberra*	341,968	405	Adelaide	158,259
New South Wales			410	Outer Adelaide	131,465
105	Sydney	4,336,374	415	Yorke and Lower North	45,979
110	Hunter	624,296	420	Murray Lands	69,763
115	Illawarra	417,901	425	South East	64,956
120	Richmond-Tweed	232,948	430	Eyre	34,893
125	Mid-North Coast	300,006	435	Northern	79,198
130	Northern	180,067	Tasmania
135	North Western	115,419	605	Greater Hobart	207,484
140	Central West	178,840	610	Southern	36,374
145	South Eastern	209,270	615	Northern	139,466
150	Murrumbidgee	154,663	620	Mersey-Lyell	110,017
155	Murray	116,471	Victoria
160	Far West	22,817	205	Melbourne	3,806,092
Northern Territory (Subdivisions)			210	Barwon	273,619
70505	Darwin City	72,859	215	Western District	103,307
70510	Palmerston-East Arm	27,145	220	Central Highlands	149,231
70520	Litchfield Shire	17,395	225	Wimmera	50,050
71005	Finniss	2,214	230	Mallee	92,707
71010	Bathurst-Melville	2,501	235	Loddon	177,340
71015	Alligator	6,913	240	Goulburn	204,254
71020	Daly	4,353	245	Ovens-Murray	97,069
71025	East Arnhem	16,077	250	East Gippsland	83,952
71030	Lower Top End NT	18,894	255	Gippsland	167,595
71035	Barkly	6,279	Western Australia
71040	Central NT	40,299	505	Perth	1,554,769
Queensland			510	South West	224,137
305	Brisbane	1,857,594	515	Lower Great Southern	55,946
307	Gold Coast	535,528	520	Upper Great Southern	18,800
309	Sunshine Coast	303,050	525	Midlands	53,593
312	West Moreton	74,328	530	South Eastern	56,858
315	Wide Bay-Burnett	275,734	535	Central	62,133
320	Darling Downs	229,254	540	Pilbara	45,277
325	South West	26,161	545	Kimberley	34,270
330	Fitzroy	204,537	Other territories		–
335	Central West	11,397	Total		21,016,884
340	Mackay	163,127
345	Northern	214,295
350	Far North	253,721
355	North West	33,336

* Includes Statistical Division 810 'Australian Capital Territory – balance'.

Rates for the different SDs were ordered into 5 groups using the Jenks Natural Breaks method which is the default multi-class numerical classification method used in ArcGIS. This classification method finds the largest breaks between natural clusters of ordered data by iteratively comparing the sum of the squared differences within the clusters and by adjusting class boundaries to minimise these differences. Another class '0' was added to account for areas with no notifications, for a total of 6 rate classes per map. Note that the classification is data dependent and changes from map to map. The 2 Statistical Divisions in the Australian Capital Territory were combined to calculate rates for the Territory as a whole.

There were 135 NNDSS postcodes which did not exist in the 2006 ABS concordance files (2006 being the latest available at time of publication) and consequently could not be mapped. These postcodes consisted of post office box numbers, special NNDSS postcode formats (3999/4999/6999/8888/9999 etc), fictitious postcodes (6444), missing postcodes and 2007 postcodes. These 135 notifications were omitted from the maps.