Australia's notifiable diseases status, 2008: Annual report of the National Notifiable Diseases Surveillance System - Methods

The Australia’s notifiable diseases status, 2008 report provides data and an analysis of communicable disease incidence in Australia during 2008. The full report is available in 16 HTML documents. The full report is also available in PDF format from the Table of contents page.

Page last updated: 30 September 2010

This article {extract} was published in Communicable Diseases Intelligence Vol 34 No 3 September 2010 and may be downloaded as a full version PDF from the Table of contents page.

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 for which personal information can be shared. The National Health Security Agreement 20083 establishes operational arrangements to formalise and enhance existing surveillance and reporting systems, an important objective of the Agreement.

Under the Agreement, in 2008 states and territories forwarded de-identified data on the nationally agreed set of 65 communicable diseases to the Department of Health and Aging for the purposes of national communicable disease surveillance, although not all 65 diseases were notifiable in each jurisdiction. States and territories provided data to the National Notifiable Diseases Surveillance System (NNDSS) electronically, daily or several times a week. The system was complemented by other surveillance systems, which provided information on various diseases, including four that are not reported to NNDSS, namely human immunodeficiency virus (HIV), acquired immune deficiency (AIDS) and the classical and variant forms of Creutzfeldt-Jakob disease (CJD).

In 2008, 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) and 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) were reported from states and territories to NNDSS but 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.

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Newly diagnosed HIV infection and AIDS were notifiable conditions in each state or territory health jurisdiction in 2008 and these data were forwarded directly 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

Surveillance of the classical and variant forms of CJD in Australia has been 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/cdnareport6 The Communicable Diseases Intelligence (CDI) quarterly journal publishes surveillance data and reports of research studies on the epidemiology and control of various communicable diseases.

Notification rates for each notifiable disease were calculated using the estimated 2008 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 2006 census data as the standard population.

The 4 maps produced for this report (chlamydia, influenza, pertussis, Q fever) were created with ArcGIS mapping software (ESRI, Redlands, CA) and based on the NNDSS notifications' residential postcode recorded in the NNDSS.

With one exception, maps were based on Statistical Divisions (SDs), as defined by the Australian Standard Geographical Classification (AGSC) (Map 1, Table 1), for all states and territories. The Northern Territory was represented by Statistical Subdivisions (SSD) and in the case of Greater Darwin, by the combination of the Tiwi Islands, Darwin, Palmerston and Litchfield SSD. This combination helped preserve confidentiality while improving legibility at the scale the maps to be printed. The geocode 77777 for Greater Darwin is only nominal.

Map 1: Australian Bureau of Statistics Statistical Division codes, Australia, and Statistical Subdivision codes, Northern Territory, 2008

Map 1:  Australian Bureau of Statistics Statistical Division codes, Australia, and Statistical Subdivision codes, Northern Territory, 2008

Table 1: Australian population by Statistical Division and Statistical Subdivision for the Northern Territory, 2008

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SD code
Statistical Division
Population
SD code
Statistical Division
Population
Australian Capital Territory
South Australia
805
Canberra
345,257
405
Adelaide
1,172,105
810
ACT balance
294
410
Outer Adelaide
134,085
New South Wales
415
Yorke and Lower North
46,396
105
Sydney
4,399,722
420
Murray Lands
70,125
110
Hunter
632,851
425
South East
65,402
115
Illawarra
423,487
430
Eyre
35,174
120
Richmond–Tweed
237,361
435
Northern
80,074
125
Mid-North Coast
304,323
Tasmania
130
Northern
181,667
605
Greater Hobart
209,287
135
North Western
116,736
610
Southern
36,875
140
Central West
180,074
615
Northern
140,275
145
South Eastern
212,238
620
Mersey–Lyell
111,092
150
Murrumbidgee
155,868
Victoria
155
Murray
117,108
205
Melbourne
3,892,419
160
Far West
22,737
210
Barwon
278,668
Northern Territory (Subdivisions)
215
Western District
104,709
71005
Finniss
2,214
220
Central Highlands
152,075
71010
Bathurst–Melville
2,501
225
Wimmera
50,404
71015
Alligator
6,913
230
Mallee
93,568
71020
Daly
4,353
235
Loddon
179,948
71025
East Arnhem
16,077
240
Goulburn
207,685
71030
Lower Top End NT
18,894
245
Ovens–Murray
98,250
71040
Central NT
40,299
250
East Gippsland
85,318
77777
Greater Darwin
123,139
255
Gippsland
170,779
Queensland
Western Australia
305
Brisbane
1,945,639
505
Perth
1,602,559
307
Gold Coast
497,848
510
South West
236,058
309
Sunshine Coast
312,804
515
Lower Great Southern
57,439
312
West Moreton
90,738
520
Upper Great Southern
18,887
315
Wide Bay–Burnett
277,965
525
Midlands
54,603
320
Darling Downs
231,599
530
South Eastern
58,074
325
South West
26,150
535
Central
63,409
330
Fitzroy
214,753
540
Pilbara
45,983
335
Central West
12,256
545
Kimberley
34,185
340
Mackay
167,666
Other territories
345
Northern
220,656
Total
21,423,938
350
Far North
262,095
 
355
North West
33,746

Source: ABS 3218.0 Regional Population Growth, Australia, 23 April 2009 (http://abs.gov.au/AUSSTATS/abs@.nsf/DetailsPage/3218.02007–08).

Notifications were summed by the postcode weighting calculated by the Australian Bureau of Statistics Postcode Concordance.8 These ABS concordance data were used to proportionally allocate notifications into SDs/SSDs according to the percentage of the population of the postcode living in the region. The total notifications per region are displayed in the relevant area.

Disease rates were calculated per 100,000 population for the relevant areas using ABS population data.7 Rates were mapped for different SDs and ordered into 5 groups using the Jenks Natural Breaks method (http://resources.arcgis.com/content/kbase?fa=articleShow&d=26442) whereby the largest breaks between natural clusters of ordered data were identified and used as class boundaries. A class '0' was added to account for areas with no notifications, resulting in a total of 6 rate classes per map. Note that the classification is data dependent and changes from map to map.

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