Australians who lived through COVID-19 might know the definition of pandemic off the top of their head. Let's shed light on some terms we use for diseases and outbreaks.
Our role is to safeguard Australia from human diseases and public health threats.
We do this by providing trusted, independent, and expert advice on disease prevention and control in Australia.
Defining a disease outbreak
An outbreak of a disease is when the occurrence of cases is higher than expected for a given population, geographical area, or time-period. It can differ from disease to disease.
This means health experts might call a small number of new cases, or even one case, of a rare disease an outbreak. But not for a similar or higher case numbers of a common condition like the flu.
Our experts, including our epidemiologists, watch disease data for expected and unexpected trends. This is why public health disease surveillance is important for detecting outbreaks.
The National Notifiable Disease Surveillance System is a source of data in Australia for the surveillance of over 80 diseases.
Endemic disease – we live with it every day
An endemic disease means that it is consistently present in a geographical area or population group.
Throughout our history, many diseases have spread to Australia and have become endemic. You will find most of these diseases elsewhere around the world, such as chickenpox or chlamydia.
Other endemic diseases might only be found in Australia, like Australian bat lyssavirus or Queensland tick typhus.
Some infections are only endemic to certain areas. For example, some diseases prefer tropical conditions and are endemic to certain areas in Australia’s north. Dengue fever is one such disease.
An epidemic – now we’re catching on
When case numbers of a disease rise more than expected, with spread across geographical areas or groups of people, we might say it’s an epidemic.
On outbreak and an epidemic have similar meanings. Usually, a disease event with greater spread across an area or population is more likely to be referred to as an epidemic.
Pandemics – when disease knows no borders
A pandemic happens when the spread of an epidemic disease no longer remains in a specific location or population group.
This could include where a disease spreads across different countries or continents and more likely affects a large number of people.
Pandemics don’t happen every day, but many diseases have caused pandemics in the past, while others have future pandemic potential.
Health experts, including at the interim Australian Centre for Disease Control, vigilantly watch for and prepare for pandemic threats.
Many initial health efforts and other policy responses aim to contain an epidemic to a certain location. It is an important step to prevent a pandemic and protect the health of large numbers of people.
Disease elimination or eradication
It is possible to eliminate a disease in a specific area.
This occurs when transmission rates reach a predetermined, very low level, but it often requires a coordinated effort over time.
Polio is one such disease – widespread vaccination has eliminated it in many countries.
Measles was officially eliminated in Australia in 2014. Australians achieved this through high vaccination coverage and ongoing epidemiological and virological surveillance.
Outbreaks of eliminated diseases can still occur, usually when an unwell traveller reintroduces the disease.
The virus that causes smallpox (variola) is the only virus that has been eradicated worldwide.
The effective smallpox vaccine and a global immunisation project led to its eradication. The last known case of smallpox occurred in 1977.