Vaccine-preventable diseases
One key group among notifiable diseases is vaccine-preventable diseases. Many of these, including rubella (22 notifications in 2019), diphtheria (7 notifications in 2019) and tetanus (3 notifications in 2019) are rare in Australia, as a result of Australia’s high immunisation rates (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.
Influenza, usually preventable by vaccination, accounts for the most notifications in Australia. Overall influenza notifications have generally increased over time but annual totals have fluctuated from year to year. There were more than 313,000 notifications in 2019, a substantial increase from 2018 (nearly 59,000 notifications). The number of influenza notifications changes 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 extent of under-notification and trends in notifications of influenza can change from year to year. Other surveillance systems are also used to determine trends in influenza to help understand the relative impact of the illness on society in Australia (Department of Health, 2019a).
The number of notifications of rotavirus, shingles and chickenpox have also risen recently. It is difficult to determine how much of the increase is due to improved diagnosis and notification and how much reflects a real increase in the number of infected people.
Sexually transmitted infections
Varying prevention and control measures are used by public health authorities depending on the type of infection or disease. Monitoring of the population groups affected by sexually transmitted infections (STIs) allows targeted prevention programs to be designed. The number of notified STIs has increased over the last decade, with chlamydia being the most commonly notified (more than 102,000 notifications in 2019). Gonorrhoea notifications have increased, but infections continue to affect the same groups: Aboriginal and Torres Strait Islander males and females in Remote or Very Remote areas, and non-Indigenous males in metropolitan settings.
Similarly, the number of notifications of infectious syphilis have increased in the last decade. New syphilis cases are diagnosed mainly in men who have sex with men in urban areas, or young Indigenous Australians in Remote or Very Remote regions. Part of the increase in numbers can be attributed to an ongoing outbreak among Indigenous Australians in Northern Australia, accounting for just over 3,000 notifications since January 2011 (Department of Health 2019b; Kirby Institute 2017).
Non-notifiable communicable 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.
Classifying non-notifiable infectious diseases
The 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 include other gastrointestinal infections, upper respiratory tract infections, lower respiratory tract infections, other meningitis and encephalitis, trachoma, abscess causing pneumonia*, otitis media, unspecified viral hepatitis, and other infections.
*not listed as a separate category in mortality coding
Hospitalisations
In 2017–18, 89% of the nearly 447,000 hospitalisations for communicable diseases were for non-notifiable diseases. From 2000–01 to 2017–18, the hospitalisation rate for non-notifiable communicable diseases peaked at 15.3 per 1,000 in 2016–17 (nearly 400,000 hospital separations). In 2017–18, the most commonly diagnosed infectious cause of hospitalisation was lower respiratory tract infections (such as pneumonia and bronchitis), accounting for almost 145,000 hospitalisations.
Influenza was the most common cause of hospitalisation for all notifiable diseases in 2017–18, with 62% of nearly 50,000 hospitalisations attributed to it. The hospitalisation rate per 1,000 population for notifiable communicable diseases has ranged between 0.8 in 2006–07 and 1.8 in 2017–18 (Figure 2).
See Hospital care.