A print friendly PDF version is available from this Communicable Diseases Intelligence issue's table of contents.

2001: the year in review

The year 2001 will be remembered for the terrorist attacks on the United States of America (USA) and the deliberate release of anthrax. A total of 22 cases of anthrax were detected and there were five deaths.¹ In response to these events, governments around the world prepared for bioterrorism by stockpiling of vaccines and antibiotics, monitoring unusual clinical presentations through 'syndromic surveillance' and strengthening laboratory capacity to test clinical and environmental samples for pathogens of biosecurity concern. The release of anthrax in the USA was followed by 'white powder incidents' in Australia and elsewhere, straining emergency, medical and laboratory services. No deliberate releases of pathogens were detected in Australia.

Improvements continued to be made in the surveillance and control of communicable diseases in Australia in 2001. Following the demonstration of high vaccine efficacy in the USA,² the seven-valent conjugate pneumococcal vaccine (7vPCV) was introduced in Australia in July 2001. A targeted vaccination schedule was developed to immunise children at high risk. Enhanced surveillance was introduced to measure the impact of vaccines on the serotype frequency and prevalence of antibiotic resistance in the pneumococci. Continued development of Australia's response to the transmissible spongiform encephalopathies included the introduction of a certification system for imported beef products in July 2001.³ The publication of Guidelines for the early clinical and public health management of meningococcal disease in Australia by the Communicable Diseases Network Australia (CDNA) in June 2001 was timely as there were a number of highly publicised clusters of meningococcal cases in Australia later in 2001.

Internationally, cases of vaccine-derived polio causing paralytic disease caused concern about the global polio eradication program. An outbreak of 21 cases of polio in Hispaniola and three cases in the Philippines occurred in communities with relatively low vaccination rates. These outbreaks demonstrate the potential of the polio virus to evade the impact of vaccination, and underline the importance of maintaining high levels of vaccination coverage.

New molecular clues to the basis of the virulence of pandemic strains of laboratory-confirmed influenza were unravelled in 2001.^4,5 The Australian Action Plan for Pandemic Influenza, updated in 2001, established plans, levels of alerts and responsibilities for the control of an influenza pandemic, were one to occur.

The surveillance of communicable diseases in Australia was further improved in 2001 by a revision of the diseases under surveillance and through the introduction of enhanced surveillance of invasive pneumococcal disease. In their first year of operation OzFoodNet, the network of foodborne disease epidemiologists in Australia, were involved in the control of two international foodborne disease outbreaks and identified 86 domestic outbreaks. The OzFoodNet report for 2001 provides valuable additional information about the epidemiology of foodborne disease in Australia.⁶

Control of communicable diseases in Australia continues to face challenges. In 2001, these included imported cases of measles causing outbreaks among unvaccinated people. Clusters of meningococcal disease in adolescents and young adults in a series of well publicised clusters in 2001 and 2002, prompted the Commonwealth Government to commence an immunisation program with the meningococcal C vaccine.

Continued improvements will need to be made to surveillance systems to manage the changing epidemiology of communicable diseases in Australia and to provide essential data for biosecurity.

Top of page

Introduction

Surveillance of communicable diseases is vital for the control of communicable diseases, to identify and assess diseases requiring control or prevention and to monitor trends over time. It is also required for the guidance of policy making.

Surveillance in Australia exists at the national, state/ territory and local levels. Primary responsibility for public health action lies with the states and territories and local health authorities.

The role of surveillance at a national level includes:

• identifying national trends in disease;
• guidance for policy development at a national level and resource allocation;
• Monitoring the need for and impact of national control programs;
• coordination of national or multi-jurisdictional outbreaks;
• description of the epidemiology of rare diseases, that occur infrequently at state and territory levels;
• meeting various international reporting requirements, such as providing disease statistics to the World Health Organization (WHO); and
• support for quarantine activities, which are a Commonwealth responsibility.

The National Notifiable Diseases Surveillance System (NNDSS) is based on fortnightly reporting by the states and territories to the Commonwealth. Fifty-five communicable diseases agreed upon nationally through CDNA are reported to NNDSS (Table 1). The system is complemented by several other surveillance systems, which provide information on other particular diseases, including some that are not reported to NNDSS.

Table 1. Diseases notified to the National Notifiable Diseases Surveillance System, Australia, 2001

Disease group	Disease	Data received from:*
Bloodborne diseases	Hepatitis B (incident)	All jurisdictions
	Hepatitis B (unspecified)	All jurisdiction, except NT
	Hepatitis C (incident)	All jurisdictions except Queensland and NT
	Hepatitis C (unspecified)	All jurisdictions
	Hepatitis D	All jurisdictions
	Hepatitis (NEC)	All jurisdictions
Gastrointestinal diseases	Botulism	All jurisdictions
	Campylobacteriosis	All jurisdictions except NSW
	Cryptosporidiosis	All jurisdictions
	Haemolytic uraemic syndrome	All jurisdictions
	Hepatitis A	All jurisdictions
	Hepatitis E	All jurisdictions
	Listeriosis	All jurisdictions
	Salmonellosis	All jurisdictions
	Shigellosis	All jurisdictions
	SLTEC,VTEC	All jurisdictions
	Typhoid	All jurisdictions
Quarantinable diseases	Cholera	All jurisdictions
	Plague	All jurisdictions
	Rabies	All jurisdictions
	Viral haemorrhagic fever	All jurisdictions
	Yellow fever	All jurisdictions
Sexually transmissible infections	Chlamydial infection	All jurisdictions
	Donovanosis	All jurisdictions except SA
	Gonococcal infection	All jurisdictions
	Syphilis	All jurisdictions
Vaccine preventable diseases	Diphtheria	All jurisdictions
	Haemophilus influenzae type b	All jurisdictions
	Laboratory-confirmed influenza	All jurisdictions
	Measles	All jurisdictions
	Mumps	All jurisdictions
	Pertussis	All jurisdictions
	Invasive pneumococcal disease	All jurisdictions
	Poliomyelitis	All jurisdictions
	Rubella	All jurisdictions
	Tetanus	All jurisdictions
Vectorborne diseases	Arbovirus infection NEC	All jurisdictions
	Barmah Forest virus infection	All jurisdictions
	Dengue	All jurisdictions
	Japanese encephalitis	All jurisdictions
	Kunjin	All jurisdictions except ACT†
	Malaria	All jurisdictions
	Murray Valley encephalitis	All jurisdictions†
	Ross River virus infection	All jurisdictions
Zoonoses	Anthrax	All jurisdictions except SA
	Australian bat lyssavirus	All jurisdictions
	Brucellosis	All jurisdictions
	Leptospirosis	All jurisdictions
	Ornithosis	All jurisdictions
	Lyssaviruses (unspecified)	All jurisdictions
	Q fever	All jurisdictions
Other bacterial infections	Legionellosis	All jurisdictions
	Leprosy	All jurisdictions
	Invasive meningococcal infection	All jurisdictions
	Tuberculosis	All jurisdictions

* Jurisdictions may not have reported a disease either because legislation had not yet made that disease notifiable in that jurisdiction, or because notification data for that disease were not reported to the Commonwealth in 2001.
† In the Australian Capital Territory, infections with Murray Valley encephalitis virus and Kunjin virus were combined under Murray Valley encephalitis
NEC: Not elsewhere classified

The results of communicable disease surveillance are reported through several avenues of communication. Fortnightly teleconferences of the CDNA provide the most up-to-date information on topics of immediate interest. The Communicable Diseases Intelligence journal, published quarterly, contains results of surveillance and research reports on the epidemiology and control of various communicable diseases. Data summaries are published on the Communicable Diseases Australia website on a fortnightly basis. The annual report of the NNDSS, Australia's notifiable diseases status, provides yearly summaries of notifications.

Top of page

Methods

Australia is a federation of six states (New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Australia) and two territories (the Australian Capital Territory and the Northern Territory). State and Territory health departments collect notifications of communicable diseases under their public health legislation. The Commonwealth Department of Health and Ageing (DoHA) does not have any legislated responsibility for public health apart from human quarantine. States and territories have agreed to forward data on nationally agreed communicable diseases to DoHA for the purposes of national communicable disease surveillance.

In 2001, data were transmitted to DoHA each fortnight by the states and territories. The Commonwealth received final data sets for 2001 from the states and territories by July 2002. Apparent errors or incomplete data for some diseases, together with any queries arising from the data, were returned to the states and territories for review.

The national data set includes fields for a unique record reference number; notifying state or territory; disease code; age; sex; Indigenous status; postcode of residence; the date of onset of the disease; and the date of report to the state or territory health department. Additional information was available on the species and serogroups isolated in cases of legionellosis, invasive meningococcal disease and malaria, and on the vaccination status in cases of childhood vaccine-preventable diseases. While not included in the national dataset, additional information concerning mortality and specific health risk factors for some diseases was obtained from states and territories.

Analyses in this report are based on date of disease onset, unless otherwise specified. For analysis of seasonal trends, notifications were reported by month of onset. Population notification rates were calculated using 2001 mid-year census-based estimates of the resident population, supplied by the Australian Bureau of Statistics (Appendix 1). Population data used in previous annual reports was based on forward projections from the 1996 census. The population calculated for the year 2001 is less than the year 2000 estimate. Comparison of rates across these years will thus be subject to slight error.

Where diseases were not notifiable in a state or territory for a particular year, adjusted rates were calculated using a denominator excluding that jurisdiction's population. The Australian Institute of Health and Welfare supplied hospital admission data for the financial year 2000-01.

Maps were generated using MapInfo, and were based on postcodes of residence, which have been allocated to Statistical Divisions by the Australian Bureau of Statistics (Map 1). The two Statistical Divisions that make up the Australian Capital Territory are combined, as the population for one division is very small. Similarly, the Darwin and 'Northern Territory - balance' Statistical Divisions have been combined to calculate rates for the Northern Territory as a whole. Rates for the different Statistical Divisions were ordered into six groups - the highest value, the lowest value (above zero) those equal to zero, and the intermediate values divided into three equal-sized groups.

Top of page

Notes on interpretation

The notifications reported to the NNDSS may be influenced by a number of factors that should be considered when interpreting the data. Due to under-reporting, notified cases can only represent a proportion of the total number of cases that occurred (Figure 1). This proportion (the 'notified fraction') varies between diseases, between states and territories and with time.

Figure 1. The communicable disease surveillance pyramid

Adopted from the Centers for Disease Control and Prevention Website: (http://www.cdc.gov/foodnet/surveillance_pages/burden_pyramid.htm)

The surveillance pyramid is a model for understanding disease reporting. This illustration shows the chain of events that must occur for an episode of illness in the population to be notified. At the bottom of the pyramid, 1) some of the general population is exposed to an organism; 2) exposed persons become ill; 3) the illness is sufficiently troubling that some persons seek care; 4) a specimen is obtained from some persons and submitted to a clinical laboratory; 5) a laboratory appropriately tests the specimen; 6) the laboratory identifies the causative organism and thereby confirms the case, or the diagnosing doctor confirms the case on clinical grounds; 7) the laboratory-confirmed or clinically-confirmed case is reported to a local or state health department, then to the Commonwealth.

Methods of surveillance can vary between states and territories, each with different requirements for notification by medical practitioners, laboratories and hospitals. In addition, the list of notifiable diseases and the case definitions may vary between states and territories.

Postcode information usually reflects the residential location of the case, but this does not necessarily represent the place where the disease was acquired. As no personal identifiers are collected in records, duplication in reporting may also occur if patients move from one jurisdiction to another and were notified in both.

The completeness of data in this report is summarised in Appendix 2. The patient's sex was missing in 0.5 per cent of notifications (n=509) and patient's age missing in 0.9 per cent of notifications (n=900). The patient's Indigenous status was reported for 55,084 (52.9%) notifications nationally. The proportion of reports with missing data in these fields varied by state and territory and by disease.

The date of disease onset is uncertain for some communicable diseases and is often equivalent to the date of presentation to a medical practitioner or date of specimen collection at a laboratory. Analysis by disease onset is an attempt to estimate disease activity within a reporting period. As considerable time may have elapsed between onset and report dates for some diseases, analyses were performed by report date for hepatitis B (unspecified) and hepatitis C (unspecified).

Between May and August every year, DoHA receives a final annual dataset from all states and territories. This yearly procedure updates only the notifications reported to NNDSS during the last calendar year. States and territories may still revise notification counts for earlier years, as duplicates are removed and other data corrected. An update of historical data for 1991 to 1999 was carried out during the year 2000 to address this issue. States and territories were also surveyed on changes in surveillance and other disease control or health promotion activities during 2001.

The present report is based on 'finalised' annual data from each state and territory, from which duplicate records or erroneous data have been removed. Totals in this report may vary slightly from the cumulative totals of the numbers reported in Communicable Diseases Intelligence. The present report has been informed by the discussions and comments of CDNA members and state and territory epidemiologists. The state and territory data managers also met through 2001, and their contribution to the accuracy of these data is gratefully acknowledged.


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