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1999: The year in review

In 1999, control of communicable diseases in Australia enjoyed some notable successes, weathered some major challenges and prepared for some major threats.

In Australia in 1999 measles and mumps were reported at record low rates in children and rubella was reported at a record low rate in women of childbearing age. This was in part the result of the Measles Control Campaign in late 1998, in which 1.7m children were immunised with a second dose of the measles-mumps-rubella vaccine. It was estimated that immunity to measles increased to 94 per cent among Australian children as a consequence of improved vaccination coverage.¹

A major challenge in 1999 was the influx into Australia of refugees from Kosovo and East Timor under the 'Safe Havens' initiative. In May and June 1999, 3,920 ethnic Albanians from Kosovo arrived in Australia. After initial processing in Sydney, refugees were accommodated in 8 centres in 5 States. There were significant presentations to medical authorities of refugees with upper respiratory tract infections, gastrointestinal illness and ear problems.² In September 1999, 1,863 people were evacuated from East Timor to Darwin. All evacuees had a mandatory health screen on arrival, 100 were admitted to hospital, 324 were reviewed in a 'fever/chest' clinic, 1,218 were reviewed in a transit camp and there were 7 births. Communicable diseases detected included 14 cases of malaria, 61 cases of tuberculosis (TB), 17 laboratory-confirmed cases of infectious diarrhoea and 3 laboratory-confirmed cases of measles and 14 suspected cases.³ Up to this time there had been no health surveillance guidelines in Australia for such a rapid response setting. Protocols for future health screening of refugees arriving in emergency situations have since been developed and published.⁴

The future of the treatment of microbial infections is increasingly uncertain given the rise of antibiotic resistant bacteria in 1999. Beta-lactamase producing vancomycin resistant Enterococcus faecilis was for the first time reported in Australia.⁵ A national response to the threat of antimicrobial resistance was the establishment of a Joint Technical Advisory Committee on Antibiotic Resistance (JETACAR). The report of this committee was released in September 1999. Details of the JETACAR report are included in this report. In response to the report, unprecedented co-operation between human and animal health practitioners has started to develop new ways to control and combat the development of antibiotic resistant microbes in Australia.

In common with other countries, Australia faces a threat of bloodborne viruses, particularly hepatitis C. Two major documents were produced in 1999, one describing the epidemiology of hepatitis C in Australia⁶ and another on an Australian plan to control hepatitis C.⁷ These 2 documents along with the Hepatitis C surveillance strategy are guiding Australia's response to the hepatitis C epidemic.

In 1999 there were important moves toward uniform baseline and enhanced disease-specific surveillance. The Communicable Diseases Network Australia New Zealand (now Communicable Diseases Network Australia), agreed in 1999 to revise the list of diseases which are designated as notifiable in Australia and to collect a more comprehensive set of data on each case. In addition, 'enhanced' surveillance systems for tuberculosis measles and hepatitis C were discussed and designed. These 'enhanced' systems aim to collect important additional information at a national level, that is critical for the surveillance and control of these diseases.
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Internationally, there was considerable concern over bovine spongiform encephalopathy (BSE) transmission to humans causing variant Creutzfeldt-Jakob disease (vCJD). There is now convincing evidence that the human disease has been caused by the consumption of foods contaminated with the BSE prion. It is still too early to predict the total number of cases of vCJD that may appear in the United Kingdom (UK) in the next two decades. In January 1999, the offspring of BSE affected cattle born after June 1996 were slaughtered in the UK, to avoid the possibility of transmission of the disease into the food chain. Deferral of blood donations from Australian citizens who were resident in the UK between 1980 and 1996 was instituted in 2000 to protect recipients from the theoretical risk that vCJD can be transmitted by blood transfusion. No cases of BSE have been found in Australian cattle herds nor have there been any cases of vCJD. The classical form of CJD does occur in Australia at a rate of 1.5 cases per million annually, consistent with international rates.⁸

In 1999, an outbreak in Malaysia and Singapore of a viral encephalitis among workers with exposure to pigs was reported.⁹ Investigations led to the identification of a previously unrecognised virus, similar to the Hendra virus which caused deaths in horses and one human handler in Queensland in 1994. The virus has since been named the Nipah virus after the area in which most infections occurred. In 1999, 265 people were infected, of whom 105 died. Consequently, 1.1 million pigs were destroyed.¹⁰ A recently published serosurvey of piggeries in Queensland confirmed that the herds were free of infection with either the Hendra or Nipah virus.¹¹

In late August 1999, an unusual clustering of cases of meningoencephalitis was reported in New York City. The cause of the outbreak was confirmed as the West Nile virus.¹² This was the first time this virus had been detected in the Western Hemisphere. Associated with the human cases were an unusually large number of deaths among birds, particularly crows. Necropsies on these birds revealed West Nile virus infection. This outbreak appears to be associated with the appearance of a new variant West Nile virus, which first appeared in Romania in 1996 and Israel in 1998.¹³ The disease has since spread along the eastern seaboard of the United States (US), and is carried by at least 14 species of mosquito. Mosquito larval control measures have limited subsequent human disease to small geographic foci. West Nile viruses are flaviviruses and are part of the 'Japanese encephalitis complex' of viruses, which include Kunjin and Murray Valley encephalitis viruses. Kunjin has been described as a subtype of lineage 1 West Nile virus. Recent studies on the relationship between Kunjin virus and West Nile virus,¹⁴ demonstrate that Kunjin virus is one of several subgroups of West Nile virus and that Australian Kunjin virus shows genetic and antigenic differences to both the West Nile virus isolated in New York in 1999 and the Kunjin virus from Malaysia. Kunjin virus is not associated with the same morbidity and mortality caused by infection with West Nile virus.

In summary, communicable disease surveillance and control in Australia was advanced in 1999 by important new initiatives and strategic control measures. The sudden influx of refugees stretched the resources of the public health system; nonetheless refugees received adequate quality medical care. Communicable diseases were diagnosed and treated and there was no spread of disease to the broader Australian community. Important new diseases have been recognised while research and surveillance suggests they will have a limited impact in Australia.

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Introduction

Surveillance of communicable diseases is an essential public health activity. Surveillance allows the detection of disease outbreaks prompting the appropriate investigation and control measures to be instigated. Surveillance also allows for the monitoring of trends in disease prevalence and considers the impact and effectiveness of interventions to control the spread of diseases. Surveillance systems exist at national, state and local levels. State and local surveillance systems are crucial to the timely and effective detection and management of outbreaks and in assisting in the effective implementation of national policies. The national surveillance system combines some of the data collected from State and Territory-based systems to provide an overview at a national level. Specific functions of the national surveillance system include: detection and management of outbreaks affecting more than one jurisdiction; monitoring the need for and impact of national control programs; guidance of national policy development; resource allocation; and description of the epidemiology of rare diseases for which there are only a few notifications in each jurisdiction. National surveillance also assists in quarantine activities and facilitates agreed international collaborations such as reporting to the World Health Organization.

The National Notifiable Diseases Surveillance System (NNDSS) was established in its current form in 1991, under the auspices of the Communicable Diseases Network Australia (CDNA, formally the Communicable Diseases Network Australia New Zealand, CDNANZ). The CDNA monitors trends of an agreed list of communicable diseases in Australia. Data are regularly published in the Communicable Diseases Intelligence (CDI) and on the Internet site Communicable Diseases Australia. This is achieved through the national collation of notifications of these diseases received by health authorities in the States and Territories. In 1999, 49 diseases or disease categories were included (Table 4), largely as recommended by the National Health and Medical Research Council (NHMRC).¹⁵ At present the list of notifiable diseases and categories is undergoing review and revision. Information collected on notifiable diseases has been published in the Annual Report of the NNDSS since 1991.^{16,17,18,19,20,21,22}

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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). The States and Territories collect notifications of communicable diseases under their public health legislation. The Commonwealth (or Federal) Government does not have any legislated responsibility for public health apart from human quarantine. States and Territories have agreed to forward data on communicable diseases to the Commonwealth Department of Health and Aged Care (DHAC) for the purposes of national communicable disease surveillance.

In 1999, the States and Territories transmitted data to the Commonwealth, fortnightly. Summaries of the data were published fortnightly on the Communicable Diseases Australia Website and in the Communicable Diseases Intelligence (CDI) every 4 weeks. The Commonwealth received final data sets from the States and Territories of cases reported in 1999, by August 2000. Where possible, missing data and apparent errors were corrected, in consultation with the States and Territories. For the purposes of the NNDSS, where a patient being treated in one jurisdiction was diagnosed in another, notifications were from the State or Territory where the case was diagnosed.

Case definitions for each disease can be found in Appendices 1a-1h. For each case, the national data set includes fields for a unique record reference number; a code for the disease; age, sex, indigenous status; postcode of residence; the date of onset of the disease and date of report to the State or Territory health authority; and the confirmation status of the report. Analysis of the data by indigenous status was not possible because of the incomplete reporting of this information. Additional information was available on the species and serogroups isolated in cases of legionellosis, brucellosis, meningococcal disease, malaria and enterotoxigenic (verotoxigenic) Escherichia coli.

Analyses in this report are based on date of disease onset. For analysis of seasonal trends, notifications were reported by month of onset. Population notification rates were calculated using 1999 mid-year estimates of the resident population supplied by the Australian Bureau of Statistics. An adjusted rate was calculated where a disease was not notifiable in a State or Territory using a denominator which excluded that population. The data were analysed in Excel.

Maps were generated using MapInfo based on the postcode of residence and allocated to Australian Bureau of Statistics Statistical Divisions (Map 1). The 2 Statistical Divisions that make up the Australian Capital Territory were combined, as the population for one Division is very small. Notifications for Darwin and the remainder of the Northern Territory were also combined to calculate rates for the Northern Territory as a whole. In general, notification rates for Statistical Divisions were depicted in maps or discussed in the text only where the number of notifications was sufficiently large for these to be meaningful.

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Notes on interpretation

The notifications compiled by the NNDSS may be influenced by a number of factors that should be considered when interpreting the data. Due to under-reporting, notified cases are likely to only represent a proportion of the total number of cases that occurred. This proportion may vary between diseases, between States and Territories and with time (Appendix 2). Methods of surveillance vary between jurisdictions, 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 jurisdictions.

Postcode information usually reflects the postcode of residence. However, the postcode of residence may not necessarily represent the place of acquisition of the disease, or the area in which public health actions were taken in response to the notification.

As no personal identifiers are collected in records, duplication in reporting may occur if patients moved from one jurisdiction to another and were notified in both. Data from those Statistical Divisions with small populations (Map 1) may result in high notification rates even with small numbers of cases. Notifications of diseases with longer incubation periods are more likely to be affected in this way than short incubation diseases.

The completeness of data in this report is summarised in Appendix 5. Missing data were patients' sex in 0.9 per cent notifications (n = 780) and patients' age in 0.3 per cent notifications (n = 256). The proportion of reports with missing data in these fields varied by State or Territory, and also by disease.

This is the first annual report where data are analysed by date of disease onset. 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. Analysis by date of onset should be interpreted with caution, particularly for chronic diseases such as hepatitis B and C. NNDSS data from previous years (1994-1998, Table 3) show totals and rates for those years as analysed in August 2000. States and Territories continue to revise totals from previous years as duplicates are removed and other data are corrected. For this reason the totals and rates shown in Table 3 differ from totals and rates published in the annual reports from these years. All comparisons in this report are to the most recent totals, which are more accurate than those previously published.

Rates per 100,000 population were calculated using State, Territory and national population estimates for mid-year 1999, suppled by the Australian Bureau of Statistics (ABS). Mortality statistics for 1999 were available from ABS in 2001. The Australian Institute of Health and Welfare (AIHW) supplied hospital admission data for the financial year 1998/1999.

Data were analysed every 4 weeks and a short report published in CDI. This report is based on 'finalised' annual data from each jurisdiction, from which duplicate or erroneous records have been removed. For this reason, totals in this report may vary from the cumulative totals of the numbers reported in the four-weekly CDI reports. This report is informed by the discussions and comments of members of the CDNA, who met fortnightly by teleconference to discuss developments in communicable disease in their jurisdiction. The contribution of State and Territory data managers, to ensure that the data in this report are accurate, is gratefully acknowledged.

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Results - surveillance notifications and reports

There was a total of 88,229 communicable disease notifications in 1999 (Table 1). Notification rates per 100,000 population for each disease by State or Territory are described in Table 2. Comparative data for 1998 and the preceding 4 years are shown in Table 3.

In 1999, cases of haemolytic uraemic syndrome became notifiable in all States and Territories and shiga-toxin producing E. Coli (SLTEC, also called verotoxigenic E. Coli (VTEC)) infections were reported in all jurisdictions except Queensland and Western Australia.

The number of notifications in 1999 was an increase of 3 per cent on notifications in 1998 (85,227) and the second largest number of reports since the NNDSS commenced in 1991 (Figure 1). In 1999 there were 29,977 bloodborne infections (34% of total), 22,255 gastrointestinal infections (25%), 21,704 sexually transmitted disease (25%), 5,986 vectorborne diseases (7%), 5,228 vaccine preventable diseases (6%), 1,967 other bacterial infections (2%), 1,012 zoonotic infections (1%) and 3 quarantinable diseases (<1%), (Figure 2).

Figure 1. Notification rate (per 100,000 population) to NNDSS, 1991 to 1999



Figure 2. Breakdown of communicable diseases notifications by disease category, 1999



The major changes in notifications in 1999 are shown in Figure 3 as a ratio of 1999 notifications compared with a 5-year mean. Only diseases with major changes in numbers of notifications in 1999 are shown. There was more than 50 per cent increase in notifications of hepatitis C (incident notifications) and leptospirosis. Smaller increases were noted in the reporting of chlamydial, gonococcal and meningococcal infections, legionellosis, mumps and syphilis. Measles notifications fell by more than 50 per cent compared with the five year mean (Figure 3). Declines in Haemophilus influenzae type b (Hib) infections and mumps were also noted.

Figure 3. Comparison of selected disease totals in 1999, with historical data (5 year mean)



In 1999, infectious and parasitic diseases (ICD-10 codes A00-B99) accounted for 1.25 per cent of all deaths in Australia (1,603 deaths). Pneumonia and influenza (ICD-10 codes J10-J18) accounted for a further 1.5 per cent of deaths (1,898 deaths). Death rates increased with age and were greater for males than females aged 45 years and over (Causes of death Australia 1999, Ausstats 3303.0 ABS, 2000).


This article was published in Communicable Diseases Intelligence Volume 25, No 4, November 2001.