Infectious and communicable diseases is an Australia's health topic

Infectious diseases are caused by infectious agents (bacteria, viruses, parasites and fungi and their toxic products). Many infectious diseases are also communicable diseases, meaning they can be passed from one person or animal to another. Transmission can occur directly (through contact with blood and bodily fluids) or indirectly (through contaminated food, water, air or surfaces) or by means of vectors (such as mosquitoes). Examples of these communicable diseases include measles (direct or indirect transmission), malaria (transmitted by mosquitoes), and chlamydia (direct transmission through sexual contact).

In some cases, the illness caused by an infectious disease is mild and short-lived and medical care is not required or sought – for example, a cold. As a result, the prevalence of many infectious diseases is difficult to measure. To assist in understanding their impact, certain infectious diseases are notifiable conditions. When a diagnosis is made of one of these diseases, a report is made to health authorities.

What are notifiable diseases?

Notifiable diseases are a subset of infectious diseases. Legislation requires that each detected case is reported to state and territory health departments. Notifiable diseases include bloodborne diseases, gastrointestinal diseases, airborne diseases, sexually transmissible infections, vaccine-preventable diseases, vector-borne diseases, zoonoses, listed human diseases (including COVID-19), and other bacterial diseases (see National notifiable disease list). 

Notification means that trends in the number and characteristics of cases can be monitored over time from a consistent and comparable data set. Outbreaks can then be detected in a timely way so that interventions can be implemented to prevent or reduce transmission. Monitoring, analysis and reporting on notifiable diseases occurs nationally via the National Notifiable Diseases Surveillance System (NNDSS). It is worth noting that cases of Human immunodeficiency virus (HIV) notifications are not available through NNDSS. For more information on HIV notifications, see UNSW Kirby Institute HIV.

This page highlights the impact of infectious diseases in Australia, both notifiable and non-notifiable.

Infectious diseases over time

Throughout the 1900s, improved sanitation and new prevention and treatment options drastically reduced the burden of infectious diseases. Immunisation and vaccination are key preventive measures against infectious and communicable diseases and have been highly successful at reducing infections from significant diseases. Australia’s high vaccination coverage, along with well-developed disease surveillance and response systems, led to Australia being declared polio-free in 2000, and achieving measles elimination in 2014. Although Australia has maintained its measles elimination status, the rise in measles cases globally has resulted in instances of imported measles cases entering the country (Doherty Institute 2023). In 2023, there were only 26 notifications for measles nationwide. For more information, see Immunisation and vaccination.

In late 2019, COVID-19 emerged as a new disease and the World Health Organization (WHO) declared it a pandemic in March 2020. By 31 March 2024, more than 775 million cases and over 7 million COVID-19 related deaths, had been confirmed worldwide (WHO 2024). However, the true numbers are likely to be much higher as many cases and deaths from COVID-19 may go undetected and unreported (COVID-19 Excess Mortality Collaborators 2022; Lau et al. 2021). In Australia, there have been nearly 12 million confirmed or probable cases of COVID-19 as at 25 March 2024 (Department of Health and Aged Care 2024). Since the start of the pandemic, a total of 22,315 people have died from or with COVID-19 in Australia (registered by 29 February 2024) (ABS 2024).

COVID-19 caused considerable burden in Australia. The total burden from COVID-19 was 48,400 DALY (1.8 DALY per 1000 population) in 2023. COVID-19 contributed 0.9% of the total disease burden in 2023, and over 34% of the burden of all infectious diseases. The burden of COVID-19 was predominantly fatal and was higher in males (AIHW 2023). For more information, see Burden of disease.

Although the burden of infectious diseases (including COVID-19) in Australia is relatively small (2.5% of total disease burden in 2023) (AIHW 2023), most people will experience an infectious disease during their lifetime – for example, a common cold or a stomach bug. Many infectious diseases have the potential to cause significant illness and outbreaks, as well as deaths. Some have developed resistance to antimicrobial agents, increasing the risk of more lengthy and complex treatment and poor outcomes (ACSQHC 2023).

Significant demographic, technological, and environmental changes in the 21st century present future threats to the spread of infectious diseases. Increased urbanisation and population density creates opportunities for more persistent infectious disease outbreaks. Globalisation increases the risk of importing and exporting pathogens. Climate change is expanding the seasonal and geographic dynamics of many infectious diseases, and is expected to be the driving cause of increasing infectious disease rates in new populations (Baker et al. 2022).

How common are infectious diseases?

We do not know the incidence of all infectious diseases in Australia, as only a subset of infectious diseases are notifiable. However, data from the National Hospitalisation Morbidity Database and the National Mortality Database give an indication on the impact of serious conditions due to infectious diseases that required hospitalisations and/or caused deaths.

Notifiable diseases

Over 1.5 million cases of notifiable diseases were reported to the NNDSS in 2023, with COVID-19 (over 837,400 cases) accounting for 54% of the total notifications.

After COVID-19, the 6 diseases with the highest number of notifications include:

  • Influenza (laboratory confirmed) – more than 290,000 notifications (19% of the total notifications)
  • Respiratory syncytial virus (RSV) – almost 129,000 notifications (8% of the total notifications)
  • Chlamydia (a sexually transmissible infection) – more than 109,000 notifications (7% of the total notifications)
  • Campylobacter (a gastrointestinal infection) – more than 41,000 notifications (3% of the total notifications)
  • Gonorrhoea (a sexually transmissible infection) – more than 40,000 notifications (3% of the total notifications)
  • Varicella zoster (which causes chickenpox and shingles) – more than 34,000 notifications combined, or about 2% of the total notifications (Figure 1).

Figure 1: Cases of notifiable infectious diseases, Australia, 2009–2023

This figure presents a line graph showing the number of notifications for various notifiable diseases between 2009 and 2023. The reader can select all notifiable diseases or specific sub-types and individual diseases. The data show that the most commonly notified bloodborne disease was hepatitis C (unspecified), the most common gastrointestinal infection was campylobacteriosis, the most common STI was chlamydia, the most common vector-borne disease was Ross River virus, the most common vaccine-preventable disease was influenza, the most common zoonotic disease was Q fever and the most common other bacterial disease was tuberculosis. The number of notifications for many diseases decreased during 2020 and 2023.

Vaccine-preventable diseases

One key group among notifiable diseases is vaccine-preventable diseases. Many of these, including rubella (3 notifications in 2023), diphtheria (13 notifications in 2023) and tetanus (4 notifications in 2023) are rare in Australia, because of Australia’s high immunisation rates. For more information, see Immunisation and vaccination. For some diseases, such as pertussis (whooping cough) and measles, the number of notifications can increase during outbreak periods because people with low or no immunity can be infected.

Up until 2019, influenza, usually preventable by vaccination, accounted for the most notifications in Australia each year. Notifications had generally increased over time, but annual totals fluctuated from year to year depending on the particular type of influenza circulating in the population, and on factors such as the amount of laboratory testing of unwell people, or the types of tests used.

The number of influenza notifications decreased substantially in 2020 and 2021. This is potentially owing to public health measures put in place to control the pandemic, such as physical distancing, international and local travel restrictions, lockdowns, mask-wearing and handwashing, which would have also affected the spread of other infectious diseases, particularly respiratory viruses (Sullivan et al. 2020). In addition, people may have been less likely than usual to seek medical care for relatively minor illnesses, leading to under-diagnosis and under-reporting for some diseases. It is difficult to determine the relative contribution of these various factors to the declines.

Following the relaxation of public health restrictions in 2022 and 2023, the number of influenza notifications increased again. In 2023, the number of influenza notifications reached the second highest number of notifications ever recorded since 2001.

Sexually transmissible infections and blood borne viruses

Significant progress has been made in the prevention and management of blood borne viruses (BBV) and sexually transmissible infections (STI) in Australia. However, diseases such as hepatitis B, hepatitis C, HIV, chlamydia and syphilis remain significant public health issues. In 2023, the most commonly notified BBV was hepatitis C (over 7,600 notifications). The HIV notification rate has generally declined over the past decade. In 2021, there were 552 new HIV diagnoses, representing a decline of 48% since 2012 (King et al. 2022). The number of notified STI has generally increased over the last decade, with chlamydia being the most commonly notified STI (more than 109,000 notifications in 2023), followed by gonorrhoea (more than 40,000 notifications in 2023), and infectious syphilis (over 6,400 notifications in 2023). Notification rates for infectious syphilis and gonorrhoea increased notably between 2013 and 2019, followed by a decrease between 2019 and 2021, which was likely due to a decline in testing during the COVID-19 pandemic. Chlamydia notification rates increased in females between 2013 and 2019, but were relatively stable in males, with rates in both sexes declining during the pandemic (King et al. 2023).

An ongoing outbreak of infectious syphilis among young Aboriginal and Torres Strait Islander (First Nations) adults in Queensland, the Northern Territory, Western Australia and South Australia has contributed to increasing numbers of STI notifications over the last decade. Since January 2011, the outbreak has resulted in more 5,600 notifications (Department of Health and Aged Care 2023a). 

In general, new syphilis cases in Australia are diagnosed mainly in men who have sex with men in urban areas, or young First Nations people in Remote or Very remote regions, although more recently increased numbers of cases have occurred among non-Indigenous women of reproductive age (15–44 years) in urban areas. Eighty-three cases of congenital syphilis (when the infection passes from a mother to her baby during pregnancy or at birth) were reported between 1 January 2016 and 30 September 2023 (Department of Health and Aged Care 2023a).

STI and BBV notifications among First Nations people are disproportionately higher than in non-Indigenous Australians. Lack of access to culturally appropriate health services for testing and treatment, combined with the effect of social determinants (see glossary), increase the risk of STI and BBV for First Nations people (King et al. 2022; Wand et al. 2016; Ward et al. 2020). Collection of information about testing for STI among First Nations people aged 15–34 was piloted in 2022 as part of the national Key Performance Indicators (nKPIs) for Indigenous-specific primary health care organisations. For more information on the nKPI collection, see Aboriginal and Torres Strait Islander specific primary health care: results from the OSR and nKPI collections.

Varying prevention and control measures are used by public health authorities depending on the type of infection. Monitoring of the priority populations most commonly affected by STI and BBV allows targeted prevention programs to be designed. The ongoing response to STI and BBV in Australia is being coordinated by the Department of Health and Aged Care through the 5 National Blood Borne Viruses and Sexually Transmissible Infections Strategies including:

  • Third National Hepatitis B Strategy 2018–2022
  • Fourth National STI Strategy 2018–2022
  • Fifth National Hepatitis C Strategy 2018–2022
  • Fifth National Aboriginal and Torres Strait Islander BBV and STI Strategy 2018–2022
  • Eighth national HIV strategy 2018-2022 (Department of Health and Aged Care 2023b).

The next iteration of the Strategies for 2024–2030 is in development, with the overarching goal of eliminating blood borne viruses and STI as public health threats by 2030. In addition, the HIV taskforce was established in 2023 to review Australia’s efforts to end the HIV epidemic, with the goal of achieving virtual elimination of HIV transmission in Australia by 2030 (Department of Health and Aged Care 2023c).

Non-notifiable diseases

Non-notifiable infectious diseases are not routinely monitored, though their impact can be tracked through assessing presentations to hospital, or through mortality data. These data sources capture the small proportion of people who have severe illness, causing hospitalisation or resulting in death. Information on hospitalisations and deaths from non-notifiable infectious diseases is presented in the following sections.

Classifying non-notifiable infectious diseases

Non-notifiable infectious diseases are broadly categorised based on the International Statistical Classification of Diseases and Related Health Problems, 10th Revision, Australian Modification (ICD-10-AM) codes for hospitalisations and International Statistical Classification of Diseases and Related Health Problems, 10th Revision (ICD-10) for deaths. The categories used here include gastrointestinal infections (other than those which are notifiable), upper respiratory tract infections, lower respiratory tract infections (excluding influenza), other meningitis and encephalitis, trachoma, abscess causing pneumonia, otitis media, unspecified viral hepatitis, and other infections. Abscess causing pneumonia is not listed as a separate category in mortality coding.

The impact of infectious diseases

Hospitalisations

In 2021, there were more than 362,600 hospitalisations for infectious diseases, of which 92% were for non-notifiable diseases. The hospitalisation rate for non-notifiable infectious diseases generally increased between 2006 and 2017, before stabilising at around 16 per 1,000 people (Figure 2). The rate dropped considerably to 11.2 per 1,000 in 2020 before increasing slightly to 13.0 per 1,000 in 2021.

Figure 2: Deaths and hospitalisations from notifiable and non-notifiable infectious diseases, numbers and rates, Australia, 2000–2022

This figure presents a line graph with 2 lines for notifiable and non-notifiable diseases. The reader can select either hospitalisations or deaths, and numbers or crude rates. The data show that hospitalisations from non-notifiable diseases were considerably more common than from notifiable diseases, but that hospitalisations decreased substantially in 2020 and 2021. Deaths from non-notifiable diseases were considerably more common than from notifiable diseases in the period between 2000 and 2021. However, in 2022, deaths from notifiable diseases were twice as high as deaths from non-notifiable diseases. The number of deaths and crude death rate increased substantially in 2022, due to a sharp increase in deaths attributed to notifiable diseases. 

The most common causes of infectious disease hospitalisation across all years were lower respiratory tract infections (including pneumonia and bronchitis, but excluding laboratory-diagnosed influenza, which is notifiable). Lower respiratory infections had been generally increasing between 2000 (4.6 hospitalisations per 1,000 people) and 2019 (5.9 per 1,000), but this fell to 3.6 per 1,000 in 2020 before rising to 4.6 per 1,000 in 2021 (Figure 3).

Figure 3: Deaths and hospitalisations from non-notifiable infectious diseases, by disease type, numbers and rates, Australia, 2000–2022

This figure presents a line graph with lines for each of the non-notifiable disease sub-types. The reader can select either hospitalisations or deaths, and numbers or crude rates. The data show that lower respiratory infections were the most common cause of hospitalisation for the period between 2001 and 2021, and of deaths for the period between 2001 and 2022.

The hospitalisation rate for notifiable infectious diseases ranged between 1.1 and 2.2 per 1,000 people over the period 2000 to 2019 but dropped to 0.8 per 1,000 in 2020 before rising again to 1.1 per 1,000 in 2021 (Figure 2). Influenza was the most common cause of notifiable disease hospitalisations in most years over the past decade, though highly variable from year to year, ranging from 1,222 to 35,672 hospitalisations (from below 0.1 to 1.4 hospitalisations per 1,000 people). In 2021, however, there were only 621 hospitalisations for influenza, a rate of 0.02 per 1,000 people. This is consistent with the fall in the number of notified cases described above.

Hospitalisations where COVID-19 infection was recorded increased from 2,631 in 2020 to 57,238 in 2021. As per Australian coding rules, in almost all cases COVID-19 was not specified as the principal diagnosis (IHPA 2021). Instead, the most common principal diagnoses recorded along with COVID-19 were viral pneumonia (24% of cases), ‘coronavirus infection’ (19%), and symptoms such as cough (9.9%), fever (6.6%) and breathing abnormalities (4.8%).

For more information on hospitalisation in Australia, see Hospitals.

Deaths

In 2022, more than 15,770 deaths in Australia were attributed to infectious diseases, a rate of 61 per 100,000 people. About a third (33%) of these deaths were attributed to non-notifiable diseases, the most common of which were lower respiratory infections (almost 2,594 deaths, 10 per 100,000) (Figures 2 and 3).

There were 9,859 deaths due to COVID-19 registered in 2022 (38 per 100,000), accounting for over 93% of all deaths attributed to notifiable diseases and 63% of all deaths attributed to infectious diseases in Australia. There were 1,122 deaths due COVID-19 in 2021 and 900 deaths in 2020, with crude death rate of 4.4 and 3.5 per 100,000 respectively. More information on deaths from COVID-19 is provided in Australia’s health 2022: data insights article The impact of a new disease: COVID-19 from 2020, 2021 and into 2022 Australia’s health 2022: data insights.

Influenza, which was the most common cause of notifiable disease deaths between 2014 and 2019, was recorded as the underlying cause of 56 deaths in 2020, 2 deaths in 2021 and 305 deaths in 2022.

For more information on deaths in Australia, see Life expectancy and deaths.

Where do I go for more information?

For more information on infectious diseases, see: